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@@ -41,13 +41,51 @@ class (either explicitly or via the conversion operators).
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called by the `adl_serializer` when `get<ns::person>()` is called.
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```cpp
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--8<-- "examples/from_json__default_constructible.cpp"
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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namespace ns
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{
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// a simple struct to model a person
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struct person
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{
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std::string name;
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std::string address;
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int age;
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};
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} // namespace ns
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namespace ns
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{
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void from_json(const json& j, person& p)
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{
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j.at("name").get_to(p.name);
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j.at("address").get_to(p.address);
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j.at("age").get_to(p.age);
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}
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} // namespace ns
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int main()
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{
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json j;
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j["name"] = "Ned Flanders";
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j["address"] = "744 Evergreen Terrace";
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j["age"] = 60;
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auto p = j.get<ns::person>();
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std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl;
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}
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```
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Output:
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```json
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--8<-- "examples/from_json__default_constructible.output"
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Ned Flanders (60) lives in 744 Evergreen Terrace
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```
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??? example "Example: (2) Non-default-constructible type"
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@@ -56,13 +94,67 @@ class (either explicitly or via the conversion operators).
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realize the conversion of a non-default-constructible type.
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```cpp
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--8<-- "examples/from_json__non_default_constructible.cpp"
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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namespace ns
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{
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// a simple struct to model a person (not default constructible)
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struct person
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{
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person(std::string n, std::string a, int aa)
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: name(std::move(n)), address(std::move(a)), age(aa)
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{}
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std::string name;
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std::string address;
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int age;
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};
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} // namespace ns
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namespace nlohmann
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{
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template <>
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struct adl_serializer<ns::person>
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{
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static ns::person from_json(const json& j)
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{
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return {j.at("name"), j.at("address"), j.at("age")};
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}
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// Here's the catch! You must provide a to_json method! Otherwise, you
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// will not be able to convert person to json, since you fully
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// specialized adl_serializer on that type
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static void to_json(json& j, ns::person p)
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{
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j["name"] = p.name;
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j["address"] = p.address;
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j["age"] = p.age;
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}
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};
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} // namespace nlohmann
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int main()
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{
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json j;
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j["name"] = "Ned Flanders";
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j["address"] = "744 Evergreen Terrace";
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j["age"] = 60;
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auto p = j.get<ns::person>();
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std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl;
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}
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```
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Output:
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```json
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--8<-- "examples/from_json__non_default_constructible.output"
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Ned Flanders (60) lives in 744 Evergreen Terrace
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```
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## See also
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@@ -1,4 +1,4 @@
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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/from_json/" rel="canonical"><link href=../ rel=prev><link href=../to_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_json - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannadl_serializerfrom_json class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_json </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></sLine truncated
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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/from_json/" rel="canonical"><link href=../ rel=prev><link href=../to_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_json - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannadl_serializerfrom_json class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_json </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></sLine truncated
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>TargetType</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ValueType</span><span class=o>></span>
|
||||
<span class=k>static</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=w> </span><span class=o>&&</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>TargetType</span><span class=o>&</span><span class=w> </span><span class=n>val</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span>
|
||||
<span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>from_json</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o><</span><span class=n>BasicJsonType</span><span class=o>></span><span class=p>(</span><span class=n>j</span><span class=p>),</span><span class=w> </span><span class=n>val</span><span class=p>)))</span>
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||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/" rel="canonical"><link href=../byte_container_with_subtype/subtype/ rel=prev><link href=from_json/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Overview - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new URL("../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannadl_serializer class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> Overview </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/" rel="canonical"><link href=../byte_container_with_subtype/subtype/ rel=prev><link href=from_json/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Overview - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new 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<svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> Overview </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </lLine truncated
|
||||
<span class=k>struct</span><span class=w> </span><span class=nc>adl_serializer</span><span class=p>;</span>
|
||||
</code></pre></div> <p>Serializer that uses <abbr title="Argument-dependent lookup">ADL</abbr> (<a href="https://en.cppreference.com/w/cpp/language/adl">Argument-Dependent Lookup</a>) to choose <code>to_json</code>/<code>from_json</code> functions from the types' namespaces.</p> <p>It is implemented similarly to</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>ValueType</span><span class=o>></span>
|
||||
<span class=k>struct</span><span class=w> </span><span class=nc>adl_serializer</span><span class=w> </span><span class=p>{</span>
|
||||
|
||||
@@ -25,13 +25,46 @@ This function is usually called by the constructors of the [basic_json](../basic
|
||||
by the `adl_serializer` when the constructor `basic_json(ns::person)` is called.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/to_json.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
namespace ns
|
||||
{
|
||||
// a simple struct to model a person
|
||||
struct person
|
||||
{
|
||||
std::string name;
|
||||
std::string address;
|
||||
int age;
|
||||
};
|
||||
} // namespace ns
|
||||
|
||||
namespace ns
|
||||
{
|
||||
void to_json(json& j, const person& p)
|
||||
{
|
||||
j = json{ {"name", p.name}, {"address", p.address}, {"age", p.age} };
|
||||
}
|
||||
} // namespace ns
|
||||
|
||||
int main()
|
||||
{
|
||||
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
|
||||
|
||||
json j = p;
|
||||
|
||||
std::cout << j << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/to_json.output"
|
||||
{"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/to_json/" rel="canonical"><link href=../from_json/ rel=prev><link href=../../json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>to_json - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/to_json/" rel="canonical"><link href=../from_json/ rel=prev><link href=../../json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>to_json - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> to_json </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/><Line truncated
|
||||
<span class=k>static</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>to_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=o>&</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>TargetType</span><span class=w> </span><span class=o>&&</span><span class=w> </span><span class=n>val</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span>
|
||||
<span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>to_json</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o><</span><span class=n>TargetType</span><span class=o>></span><span class=p>(</span><span class=n>val</span><span class=p>))))</span>
|
||||
<span class=o>-></span><span class=w> </span><span class=k>decltype</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>to_json</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o><</span><span class=n>TargetType</span><span class=o>></span><span class=p>(</span><span class=n>val</span><span class=p>)),</span><span class=w> </span><span class=kt>void</span><span class=p>())</span>
|
||||
|
||||
+69
-2
@@ -285,6 +285,7 @@ Access to the JSON value
|
||||
### JSON Merge Patch functions
|
||||
|
||||
- [**merge_patch**](merge_patch.md) - applies a JSON Merge Patch
|
||||
- [**merge_diff**](merge_diff.md) (_static_) - creates a diff as a JSON Merge Patch
|
||||
|
||||
## Static functions
|
||||
|
||||
@@ -330,13 +331,79 @@ Access to the JSON value
|
||||
The example shows how the library is used.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/README.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON object
|
||||
json j =
|
||||
{
|
||||
{"pi", 3.141},
|
||||
{"happy", true},
|
||||
{"name", "Niels"},
|
||||
{"nothing", nullptr},
|
||||
{
|
||||
"answer", {
|
||||
{"everything", 42}
|
||||
}
|
||||
},
|
||||
{"list", {1, 0, 2}},
|
||||
{
|
||||
"object", {
|
||||
{"currency", "USD"},
|
||||
{"value", 42.99}
|
||||
}
|
||||
}
|
||||
};
|
||||
|
||||
// add new values
|
||||
j["new"]["key"]["value"] = {"another", "list"};
|
||||
|
||||
// count elements
|
||||
auto s = j.size();
|
||||
j["size"] = s;
|
||||
|
||||
// pretty print with indent of 4 spaces
|
||||
std::cout << std::setw(4) << j << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/README.output"
|
||||
{
|
||||
"answer": {
|
||||
"everything": 42
|
||||
},
|
||||
"happy": true,
|
||||
"list": [
|
||||
1,
|
||||
0,
|
||||
2
|
||||
],
|
||||
"name": "Niels",
|
||||
"new": {
|
||||
"key": {
|
||||
"value": [
|
||||
"another",
|
||||
"list"
|
||||
]
|
||||
}
|
||||
},
|
||||
"nothing": null,
|
||||
"object": {
|
||||
"currency": "USD",
|
||||
"value": 42.99
|
||||
},
|
||||
"pi": 3.141,
|
||||
"size": 8
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -101,13 +101,40 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
|
||||
The example below demonstrates the `accept()` function reading from a string.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/accept__string.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// a valid JSON text
|
||||
auto valid_text = R"(
|
||||
{
|
||||
"numbers": [1, 2, 3]
|
||||
}
|
||||
)";
|
||||
|
||||
// an invalid JSON text
|
||||
auto invalid_text = R"(
|
||||
{
|
||||
"strings": ["extra", "comma", ]
|
||||
}
|
||||
)";
|
||||
|
||||
std::cout << std::boolalpha
|
||||
<< json::accept(valid_text) << ' '
|
||||
<< json::accept(invalid_text) << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/accept__string.output"
|
||||
true false
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) reading from an iterator pair"
|
||||
@@ -116,13 +143,29 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
|
||||
exactly the JSON text; the second one also covers the trailing bytes and is therefore rejected.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/accept__iterator_pair.cpp"
|
||||
#include <iostream>
|
||||
#include <vector>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// a buffer containing a JSON text followed by more data
|
||||
std::vector<std::uint8_t> input = {'[', '1', ',', '2', ',', '3', ']', 'o', 't', 'h', 'e', 'r'};
|
||||
|
||||
std::cout << std::boolalpha
|
||||
<< json::accept(input.begin(), input.begin() + 7) << ' '
|
||||
<< json::accept(input.begin(), input.end()) << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/accept__iterator_pair.output"
|
||||
true false
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/accept/" rel="canonical"><link href=../~basic_json/ rel=prev><link href=../array/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>accept - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> accept </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </labeLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/accept/" rel="canonical"><link href=../~basic_json/ rel=prev><link href=../array/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>accept - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonaccept class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> accept </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </labeLine truncated
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>></span>
|
||||
<span class=k>static</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>accept</span><span class=p>(</span><span class=n>InputType</span><span class=o>&&</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_comments</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
|
||||
|
||||
+25
-2
@@ -41,13 +41,36 @@ This function is only needed to express two edge cases that cannot be realized w
|
||||
The following code shows an example for the `array` function.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/array.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON arrays
|
||||
json j_no_init_list = json::array();
|
||||
json j_empty_init_list = json::array({});
|
||||
json j_nonempty_init_list = json::array({1, 2, 3, 4});
|
||||
json j_list_of_pairs = json::array({ {"one", 1}, {"two", 2} });
|
||||
|
||||
// serialize the JSON arrays
|
||||
std::cout << j_no_init_list << '\n';
|
||||
std::cout << j_empty_init_list << '\n';
|
||||
std::cout << j_nonempty_init_list << '\n';
|
||||
std::cout << j_list_of_pairs << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/array.output"
|
||||
[]
|
||||
[]
|
||||
[1,2,3,4]
|
||||
[["one",1],["two",2]]
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/array/" rel="canonical"><link href=../accept/ rel=prev><link href=../array_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonarray class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> array </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <divLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/array/" rel="canonical"><link href=../accept/ rel=prev><link href=../array_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonarray class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> array </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <divLine truncated
|
||||
</code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> array value from a given initializer list. That is, given a list of values <code>a, b, c</code>, creates the <abbr title="JavaScript Object Notation">JSON</abbr> value <code class=highlight><span class=p>[</span><span class=err>a</span><span class=p>,</span><span class=w> </span><span class=err>b</span><span class=p>,</span><span class=w> </span><span class=err>c</span><span class=p>]</span></code>. If the initializer list is empty, the empty array <code class=highlight><span class=p>[]</span></code> is created.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>init</code> (in)</dt> <dd>initializer list with <abbr title="JavaScript Object Notation">JSON</abbr> values to create an array from (optional)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> array value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of <code>init</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (<a href=../basic_json/ ><code>basic_json(initializer_list_t, bool, value_t)</code></a>). These cases are:</p> <ol> <li>creating an array whose elements are all pairs whose first element is a string -- in this case, the initializer list constructor would create an object, taking the first elements as keys</li> <li>creating an empty array -- passing the empty initializer list to the initializer list constructor yields an empty object</li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for the <code>array</code> function.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
|
||||
@@ -58,13 +58,24 @@ Arrays are stored as pointers in a `basic_json` type. That is, for any access to
|
||||
The following code shows that `array_t` is by default, a typedef to `#!cpp std::vector<nlohmann::json>`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/array_t.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
std::cout << std::boolalpha << std::is_same<std::vector<json>, json::array_t>::value << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/array_t.output"
|
||||
true
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/array_t/" rel="canonical"><link href=../array/ rel=prev><link href=../as_base_class/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonarray_t class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/array_t/" rel="canonical"><link href=../array/ rel=prev><link href=../as_base_class/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> arrays.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> arrays as follows:</p> <blockquote> <p>An array is an ordered sequence of zero or more values.</p> </blockquote> <p>To store objects in C++, a type is defined by the template parameters explained below.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ArrayType</code></dt> <dd>container type to store arrays. It must be a vector-like container: the library uses <code>operator[]</code>, <code>at()</code>, and <code>resize()</code>, and requires random-access iterators. <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span></code> and <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> qualify; <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span></code> does not. See <a href=../../../features/types/template_parameters/#arraytype>Template Parameter Requirements</a> for the full list of requirements.</dd> <dt><code>AllocatorType</code></dt> <dd>the allocator to use for objects (e.g., <code>std::allocator</code>)</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>ArrayType</code> (<code>std::vector</code>) and <code>AllocatorType</code> (<code>std::allocator</code>), the default value for <code>array_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span>
|
||||
<span class=w> </span><span class=n>basic_json</span><span class=p>,</span><span class=w> </span><span class=c1>// value_type</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>allocator</span><span class=o><</span><span class=n>basic_json</span><span class=o>></span><span class=w> </span><span class=c1>// allocator_type</span>
|
||||
|
||||
@@ -35,13 +35,44 @@ The function is equivalent to `static_cast<json_base_class_t&>(j)` (or `static_c
|
||||
of `basic_json`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/as_base_class.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
class base_class_with_hidden_members
|
||||
{
|
||||
public:
|
||||
const char* type_name() const noexcept
|
||||
{
|
||||
return "my_type_name";
|
||||
}
|
||||
|
||||
std::size_t size() const noexcept
|
||||
{
|
||||
return 42;
|
||||
}
|
||||
};
|
||||
|
||||
using json = nlohmann::json::with_base_class_t<base_class_with_hidden_members>;
|
||||
|
||||
int main()
|
||||
{
|
||||
json j = {1, 2, 3};
|
||||
|
||||
// the members of basic_json hide the members of the base class
|
||||
std::cout << j.type_name() << ' ' << j.size() << '\n';
|
||||
|
||||
// access the hidden members of the base class
|
||||
std::cout << j.as_base_class().type_name() << ' ' << j.as_base_class().size() << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/as_base_class.output"
|
||||
array 3
|
||||
my_type_name 42
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/as_base_class/" rel="canonical"><link href=../array_t/ rel=prev><link href=../at/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>as_base_class - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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|
||||
<span class=k>const</span><span class=w> </span><span class=n>json_base_class_t</span><span class=o>&</span><span class=w> </span><span class=nf>as_base_class</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
|
||||
</code></pre></div> <p>Returns a reference to this object as its custom base class <a href=../json_base_class_t/ ><code>json_base_class_t</code></a>. No copy is made.</p> <p>Since <code>basic_json</code> derives from <code>json_base_class_t</code>, a member of <code>basic_json</code> hides any member of the custom base class with the same name. This function makes such hidden members accessible again.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>reference to this object as <a href=../json_base_class_t/ ><code>json_base_class_t</code></a></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>The function is equivalent to <code>static_cast<json_base_class_t&>(j)</code> (or <code>static_cast<const json_base_class_t&>(j)</code>).</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how to use <code>as_base_class</code> to access members of the custom base class that are hidden by members of <code>basic_json</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
+502
-17
@@ -114,13 +114,59 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
exceptions that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__size_type.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON array
|
||||
json array = {"first", "2nd", "third", "fourth"};
|
||||
|
||||
// output element at index 2 (third element)
|
||||
std::cout << array.at(2) << '\n';
|
||||
|
||||
// change element at index 1 (second element) to "second"
|
||||
array.at(1) = "second";
|
||||
|
||||
// output changed array
|
||||
std::cout << array << '\n';
|
||||
|
||||
// exception type_error.304
|
||||
try
|
||||
{
|
||||
// use at() on a non-array type
|
||||
json str = "I am a string";
|
||||
str.at(0) = "Another string";
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to write beyond the array limit
|
||||
array.at(5) = "sixth";
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__size_type.output"
|
||||
"third"
|
||||
["first","second","third","fourth"]
|
||||
[json.exception.type_error.304] cannot use at() with string
|
||||
[json.exception.out_of_range.401] array index 5 is out of range
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (1) access specified array element with bounds checking"
|
||||
@@ -129,13 +175,52 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__size_type_const.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON array
|
||||
const json array = {"first", "2nd", "third", "fourth"};
|
||||
|
||||
// output element at index 2 (third element)
|
||||
std::cout << array.at(2) << '\n';
|
||||
|
||||
// exception type_error.304
|
||||
try
|
||||
{
|
||||
// use at() on a non-array type
|
||||
const json str = "I am a string";
|
||||
std::cout << str.at(0) << '\n';
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to read beyond the array limit
|
||||
std::cout << array.at(5) << '\n';
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__size_type_const.output"
|
||||
"third"
|
||||
[json.exception.type_error.304] cannot use at() with string
|
||||
[json.exception.out_of_range.401] array index 5 is out of range
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) access specified object element with bounds checking"
|
||||
@@ -144,13 +229,64 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
exceptions that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__object_t_key_type.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON object
|
||||
json object =
|
||||
{
|
||||
{"the good", "il buono"},
|
||||
{"the bad", "il cattivo"},
|
||||
{"the ugly", "il brutto"}
|
||||
};
|
||||
|
||||
// output element with key "the ugly"
|
||||
std::cout << object.at("the ugly") << '\n';
|
||||
|
||||
// change element with key "the bad"
|
||||
object.at("the bad") = "il cattivo";
|
||||
|
||||
// output changed array
|
||||
std::cout << object << '\n';
|
||||
|
||||
// exception type_error.304
|
||||
try
|
||||
{
|
||||
// use at() on a non-object type
|
||||
json str = "I am a string";
|
||||
str.at("the good") = "Another string";
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to write at a nonexisting key
|
||||
object.at("the fast") = "il rapido";
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__object_t_key_type.output"
|
||||
"il brutto"
|
||||
{"the bad":"il cattivo","the good":"il buono","the ugly":"il brutto"}
|
||||
[json.exception.type_error.304] cannot use at() with string
|
||||
[json.exception.out_of_range.403] key 'the fast' not found
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) access specified object element with bounds checking"
|
||||
@@ -159,13 +295,57 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__object_t_key_type_const.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON object
|
||||
const json object =
|
||||
{
|
||||
{"the good", "il buono"},
|
||||
{"the bad", "il cattivo"},
|
||||
{"the ugly", "il brutto"}
|
||||
};
|
||||
|
||||
// output element with key "the ugly"
|
||||
std::cout << object.at("the ugly") << '\n';
|
||||
|
||||
// exception type_error.304
|
||||
try
|
||||
{
|
||||
// use at() on a non-object type
|
||||
const json str = "I am a string";
|
||||
std::cout << str.at("the good") << '\n';
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to read from a nonexisting key
|
||||
std::cout << object.at("the fast") << '\n';
|
||||
}
|
||||
catch (const json::out_of_range)
|
||||
{
|
||||
std::cout << "out of range" << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__object_t_key_type_const.output"
|
||||
"il brutto"
|
||||
[json.exception.type_error.304] cannot use at() with string
|
||||
out of range
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (3) access specified object element using string_view with bounds checking"
|
||||
@@ -174,13 +354,66 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
exceptions that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__keytype.c++17.cpp"
|
||||
#include <iostream>
|
||||
#include <string_view>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using namespace std::string_view_literals;
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON object
|
||||
json object =
|
||||
{
|
||||
{"the good", "il buono"},
|
||||
{"the bad", "il cattivo"},
|
||||
{"the ugly", "il brutto"}
|
||||
};
|
||||
|
||||
// output element with key "the ugly" using string_view
|
||||
std::cout << object.at("the ugly"sv) << '\n';
|
||||
|
||||
// change element with key "the bad" using string_view
|
||||
object.at("the bad"sv) = "il cattivo";
|
||||
|
||||
// output changed array
|
||||
std::cout << object << '\n';
|
||||
|
||||
// exception type_error.304
|
||||
try
|
||||
{
|
||||
// use at() with string_view on a non-object type
|
||||
json str = "I am a string";
|
||||
str.at("the good"sv) = "Another string";
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to write at a nonexisting key using string_view
|
||||
object.at("the fast"sv) = "il rapido";
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__keytype.c++17.output"
|
||||
"il brutto"
|
||||
{"the bad":"il cattivo","the good":"il buono","the ugly":"il brutto"}
|
||||
[json.exception.type_error.304] cannot use at() with string
|
||||
[json.exception.out_of_range.403] key 'the fast' not found
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (3) access specified object element using string_view with bounds checking"
|
||||
@@ -189,13 +422,59 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__keytype_const.c++17.cpp"
|
||||
#include <iostream>
|
||||
#include <string_view>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using namespace std::string_view_literals;
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON object
|
||||
const json object =
|
||||
{
|
||||
{"the good", "il buono"},
|
||||
{"the bad", "il cattivo"},
|
||||
{"the ugly", "il brutto"}
|
||||
};
|
||||
|
||||
// output element with key "the ugly" using string_view
|
||||
std::cout << object.at("the ugly"sv) << '\n';
|
||||
|
||||
// exception type_error.304
|
||||
try
|
||||
{
|
||||
// use at() with string_view on a non-object type
|
||||
const json str = "I am a string";
|
||||
std::cout << str.at("the good"sv) << '\n';
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to read from a nonexisting key using string_view
|
||||
std::cout << object.at("the fast"sv) << '\n';
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << "out of range" << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__keytype_const.c++17.output"
|
||||
"il brutto"
|
||||
[json.exception.type_error.304] cannot use at() with string
|
||||
out of range
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (4) access specified element via JSON Pointer"
|
||||
@@ -204,13 +483,128 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
exceptions that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__json_pointer.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
json j =
|
||||
{
|
||||
{"number", 1}, {"string", "foo"}, {"array", {1, 2}}
|
||||
};
|
||||
|
||||
// read-only access
|
||||
|
||||
// output element with JSON pointer "/number"
|
||||
std::cout << j.at("/number"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/string"
|
||||
std::cout << j.at("/string"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/array"
|
||||
std::cout << j.at("/array"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/array/1"
|
||||
std::cout << j.at("/array/1"_json_pointer) << '\n';
|
||||
|
||||
// writing access
|
||||
|
||||
// change the string
|
||||
j.at("/string"_json_pointer) = "bar";
|
||||
// output the changed string
|
||||
std::cout << j["string"] << '\n';
|
||||
|
||||
// change an array element
|
||||
j.at("/array/1"_json_pointer) = 21;
|
||||
// output the changed array
|
||||
std::cout << j["array"] << '\n';
|
||||
|
||||
// out_of_range.106
|
||||
try
|
||||
{
|
||||
// try to use an array index with leading '0'
|
||||
json::reference ref = j.at("/array/01"_json_pointer);
|
||||
}
|
||||
catch (const json::parse_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.109
|
||||
try
|
||||
{
|
||||
// try to use an array index that is not a number
|
||||
json::reference ref = j.at("/array/one"_json_pointer);
|
||||
}
|
||||
catch (const json::parse_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to use an invalid array index
|
||||
json::reference ref = j.at("/array/4"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.402
|
||||
try
|
||||
{
|
||||
// try to use the array index '-'
|
||||
json::reference ref = j.at("/array/-"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.403
|
||||
try
|
||||
{
|
||||
// try to use a JSON pointer to a nonexistent object key
|
||||
json::const_reference ref = j.at("/foo"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.404
|
||||
try
|
||||
{
|
||||
// try to use a JSON pointer that cannot be resolved
|
||||
json::reference ref = j.at("/number/foo"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__json_pointer.output"
|
||||
1
|
||||
"foo"
|
||||
[1,2]
|
||||
2
|
||||
"bar"
|
||||
[1,21]
|
||||
[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'
|
||||
[json.exception.parse_error.109] parse error: array index 'one' is not a number
|
||||
[json.exception.out_of_range.401] array index 4 is out of range
|
||||
[json.exception.out_of_range.402] array index '-' (2) is out of range
|
||||
[json.exception.out_of_range.403] key 'foo' not found
|
||||
[json.exception.out_of_range.404] unresolved reference token 'foo'
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (4) access specified element via JSON Pointer"
|
||||
@@ -219,13 +613,102 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__json_pointer_const.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
const json j =
|
||||
{
|
||||
{"number", 1}, {"string", "foo"}, {"array", {1, 2}}
|
||||
};
|
||||
|
||||
// read-only access
|
||||
|
||||
// output element with JSON pointer "/number"
|
||||
std::cout << j.at("/number"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/string"
|
||||
std::cout << j.at("/string"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/array"
|
||||
std::cout << j.at("/array"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/array/1"
|
||||
std::cout << j.at("/array/1"_json_pointer) << '\n';
|
||||
|
||||
// out_of_range.109
|
||||
try
|
||||
{
|
||||
// try to use an array index that is not a number
|
||||
json::const_reference ref = j.at("/array/one"_json_pointer);
|
||||
}
|
||||
catch (const json::parse_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to use an invalid array index
|
||||
json::const_reference ref = j.at("/array/4"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.402
|
||||
try
|
||||
{
|
||||
// try to use the array index '-'
|
||||
json::const_reference ref = j.at("/array/-"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.403
|
||||
try
|
||||
{
|
||||
// try to use a JSON pointer to a nonexistent object key
|
||||
json::const_reference ref = j.at("/foo"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.404
|
||||
try
|
||||
{
|
||||
// try to use a JSON pointer that cannot be resolved
|
||||
json::const_reference ref = j.at("/number/foo"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__json_pointer_const.output"
|
||||
1
|
||||
"foo"
|
||||
[1,2]
|
||||
2
|
||||
[json.exception.parse_error.109] parse error: array index 'one' is not a number
|
||||
[json.exception.out_of_range.401] array index 4 is out of range
|
||||
[json.exception.out_of_range.402] array index '-' (2) is out of range
|
||||
[json.exception.out_of_range.403] key 'foo' not found
|
||||
[json.exception.out_of_range.404] unresolved reference token 'foo'
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -241,4 +724,6 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
|
||||
already supported by [`operator[]`](operator[].md), [`value`](value.md), [`find`](find.md), and other lookup
|
||||
functions.
|
||||
4. Added in version 2.0.0.
|
||||
4. Added in version 2.0.0. Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) instead of
|
||||
[`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) for a one-character array index that is not
|
||||
a digit (e.g., `/x`) in version 3.13.0, as it already did for longer ones.
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/at/" rel="canonical"><link href=../as_base_class/ rel=prev><link href=../back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>at - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonat class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> at </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=mLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/at/" rel="canonical"><link href=../as_base_class/ rel=prev><link href=../back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>at - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonat class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> at </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=mLine truncated
|
||||
<span class=n>reference</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>size_type</span><span class=w> </span><span class=n>idx</span><span class=p>);</span>
|
||||
<span class=n>const_reference</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>size_type</span><span class=w> </span><span class=n>idx</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
|
||||
@@ -498,4 +498,4 @@
|
||||
<span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>402</span><span class=p>]</span><span class=w> </span><span class=err>array</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>dex</span><span class=w> </span><span class=err>'</span><span class=mi>-</span><span class=err>'</span><span class=w> </span><span class=err>(</span><span class=mi>2</span><span class=err>)</span><span class=w> </span><span class=err>is</span><span class=w> </span><span class=err>ou</span><span class=kc>t</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>ra</span><span class=kc>n</span><span class=err>ge</span>
|
||||
<span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>403</span><span class=p>]</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=err>'</span><span class=kc>f</span><span class=err>oo'</span><span class=w> </span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=w> </span><span class=kc>f</span><span class=err>ou</span><span class=kc>n</span><span class=err>d</span>
|
||||
<span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>404</span><span class=p>]</span><span class=w> </span><span class=err>u</span><span class=kc>nres</span><span class=err>olved</span><span class=w> </span><span class=err>re</span><span class=kc>feren</span><span class=err>ce</span><span class=w> </span><span class=kc>t</span><span class=err>oke</span><span class=kc>n</span><span class=w> </span><span class=err>'</span><span class=kc>f</span><span class=err>oo'</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li>documentation on <a href=../../../features/element_access/checked_access/ >checked access</a></li> <li><a href=../operator%5B%5D/ ><code>operator[]</code></a> for unchecked access by reference</li> <li><a href=../value/ ><code>value</code></a> for access with default value</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 1.0.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 3.11.0. Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to consistently accept <code>std::string_view</code>-convertible keys, as already supported by <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../value/ ><code>value</code></a>, <a href=../find/ ><code>find</code></a>, and other lookup functions.</li> <li>Added in version 2.0.0.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 09:46:32 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.Line truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li>documentation on <a href=../../../features/element_access/checked_access/ >checked access</a></li> <li><a href=../operator%5B%5D/ ><code>operator[]</code></a> for unchecked access by reference</li> <li><a href=../value/ ><code>value</code></a> for access with default value</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 1.0.0.</li> <li>Added in version 1.0.0.</li> <li>Added in version 3.11.0. Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to consistently accept <code>std::string_view</code>-convertible keys, as already supported by <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../value/ ><code>value</code></a>, <a href=../find/ ><code>find</code></a>, and other lookup functions.</li> <li>Added in version 2.0.0. Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> instead of <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> for a one-character array index that is not a digit (e.g., <code>/x</code>) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, as it already did for longer ones.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:41 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5Line truncated
|
||||
@@ -675,4 +675,4 @@ Output:
|
||||
1. Added in version 1.0.0.
|
||||
1. Added in version 1.0.0.
|
||||
1. Added in version 3.11.0. Fixed in version 3.13.0 unreleased to consistently accept `std::string_view`-convertible keys, as already supported by [`operator[]`](https://json.nlohmann.me/api/basic_json/operator%5B%5D/index.md), [`value`](https://json.nlohmann.me/api/basic_json/value/index.md), [`find`](https://json.nlohmann.me/api/basic_json/find/index.md), and other lookup functions.
|
||||
1. Added in version 2.0.0.
|
||||
1. Added in version 2.0.0. Throws [`parse_error.109`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error109) instead of [`out_of_range.404`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range404) for a one-character array index that is not a digit (e.g., `/x`) in version 3.13.0 unreleased, as it already did for longer ones.
|
||||
+47
-2
@@ -46,13 +46,58 @@ Constant.
|
||||
The following code shows an example for `back()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/back.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json j_boolean = true;
|
||||
json j_number_integer = 17;
|
||||
json j_number_float = 23.42;
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
json j_object_empty(json::value_t::object);
|
||||
json j_array = {1, 2, 4, 8, 16};
|
||||
json j_array_empty(json::value_t::array);
|
||||
json j_string = "Hello, world";
|
||||
|
||||
// call back()
|
||||
std::cout << j_boolean.back() << '\n';
|
||||
std::cout << j_number_integer.back() << '\n';
|
||||
std::cout << j_number_float.back() << '\n';
|
||||
std::cout << j_object.back() << '\n';
|
||||
//std::cout << j_object_empty.back() << '\n'; // undefined behavior
|
||||
std::cout << j_array.back() << '\n';
|
||||
//std::cout << j_array_empty.back() << '\n'; // undefined behavior
|
||||
std::cout << j_string.back() << '\n';
|
||||
|
||||
// back() called on a null value
|
||||
try
|
||||
{
|
||||
json j_null;
|
||||
j_null.back();
|
||||
}
|
||||
catch (const json::invalid_iterator& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/back.output"
|
||||
true
|
||||
17
|
||||
23.42
|
||||
2
|
||||
16
|
||||
"Hello, world"
|
||||
[json.exception.invalid_iterator.214] cannot get value
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/back/" rel="canonical"><link href=../at/ rel=prev><link href=../begin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/back/" rel="canonical"><link href=../at/ rel=prev><link href=../begin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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|
||||
|
||||
<span class=n>const_reference</span><span class=w> </span><span class=nf>back</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
</code></pre></div> <p>Returns a reference to the last element in the container. For a <abbr title="JavaScript Object Notation">JSON</abbr> container <code>c</code>, the expression <code>c.back()</code> is equivalent to</p> <div class=highlight><pre><span></span><code><span class=k>auto</span><span class=w> </span><span class=n>tmp</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>c</span><span class=p>.</span><span class=n>end</span><span class=p>();</span>
|
||||
|
||||
+467
-18
@@ -336,13 +336,45 @@ basic_json(basic_json&& other) noexcept;
|
||||
The following code shows the constructor for different `value_t` values.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__value_t.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create the different JSON values with default values
|
||||
json j_null(json::value_t::null);
|
||||
json j_boolean(json::value_t::boolean);
|
||||
json j_number_integer(json::value_t::number_integer);
|
||||
json j_number_float(json::value_t::number_float);
|
||||
json j_object(json::value_t::object);
|
||||
json j_array(json::value_t::array);
|
||||
json j_string(json::value_t::string);
|
||||
|
||||
// serialize the JSON values
|
||||
std::cout << j_null << '\n';
|
||||
std::cout << j_boolean << '\n';
|
||||
std::cout << j_number_integer << '\n';
|
||||
std::cout << j_number_float << '\n';
|
||||
std::cout << j_object << '\n';
|
||||
std::cout << j_array << '\n';
|
||||
std::cout << j_string << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__value_t.output"
|
||||
null
|
||||
false
|
||||
0
|
||||
0.0
|
||||
{}
|
||||
[]
|
||||
""
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) create a `#!json null` object"
|
||||
@@ -350,13 +382,31 @@ basic_json(basic_json&& other) noexcept;
|
||||
The following code shows the constructor with and without a null pointer parameter.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__nullptr_t.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// implicitly create a JSON null value
|
||||
json j1;
|
||||
|
||||
// explicitly create a JSON null value
|
||||
json j2(nullptr);
|
||||
|
||||
// serialize the JSON null value
|
||||
std::cout << j1 << '\n' << j2 << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__nullptr_t.output"
|
||||
null
|
||||
null
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (3) create a JSON value from compatible types"
|
||||
@@ -364,13 +414,266 @@ basic_json(basic_json&& other) noexcept;
|
||||
The following code shows the constructor with several compatible types.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__CompatibleType.cpp"
|
||||
#include <iostream>
|
||||
#include <deque>
|
||||
#include <list>
|
||||
#include <forward_list>
|
||||
#include <set>
|
||||
#include <unordered_map>
|
||||
#include <unordered_set>
|
||||
#include <valarray>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// ============
|
||||
// object types
|
||||
// ============
|
||||
|
||||
// create an object from an object_t value
|
||||
json::object_t object_value = { {"one", 1}, {"two", 2} };
|
||||
json j_object_t(object_value);
|
||||
|
||||
// create an object from std::map
|
||||
std::map<std::string, int> c_map
|
||||
{
|
||||
{"one", 1}, {"two", 2}, {"three", 3}
|
||||
};
|
||||
json j_map(c_map);
|
||||
|
||||
// create an object from std::unordered_map
|
||||
std::unordered_map<const char*, double> c_umap
|
||||
{
|
||||
{"one", 1.2}, {"two", 2.3}, {"three", 3.4}
|
||||
};
|
||||
json j_umap(c_umap);
|
||||
|
||||
// create an object from std::multimap
|
||||
std::multimap<std::string, bool> c_mmap
|
||||
{
|
||||
{"one", true}, {"two", true}, {"three", false}, {"three", true}
|
||||
};
|
||||
json j_mmap(c_mmap); // only one entry for key "three" is used
|
||||
|
||||
// create an object from std::unordered_multimap
|
||||
std::unordered_multimap<std::string, bool> c_ummap
|
||||
{
|
||||
{"one", true}, {"two", true}, {"three", false}, {"three", false}
|
||||
};
|
||||
json j_ummap(c_ummap); // only one entry for key "three" is used
|
||||
|
||||
// serialize the JSON objects
|
||||
std::cout << j_object_t << '\n';
|
||||
std::cout << j_map << '\n';
|
||||
std::cout << j_umap << '\n';
|
||||
std::cout << j_mmap << '\n';
|
||||
std::cout << j_ummap << "\n\n";
|
||||
|
||||
// ===========
|
||||
// array types
|
||||
// ===========
|
||||
|
||||
// create an array from an array_t value
|
||||
json::array_t array_value = {"one", "two", 3, 4.5, false};
|
||||
json j_array_t(array_value);
|
||||
|
||||
// create an array from std::vector
|
||||
std::vector<int> c_vector {1, 2, 3, 4};
|
||||
json j_vec(c_vector);
|
||||
|
||||
// create an array from std::valarray
|
||||
std::valarray<short> c_valarray {10, 9, 8, 7};
|
||||
json j_valarray(c_valarray);
|
||||
|
||||
// create an array from std::deque
|
||||
std::deque<double> c_deque {1.2, 2.3, 3.4, 5.6};
|
||||
json j_deque(c_deque);
|
||||
|
||||
// create an array from std::list
|
||||
std::list<bool> c_list {true, true, false, true};
|
||||
json j_list(c_list);
|
||||
|
||||
// create an array from std::forward_list
|
||||
std::forward_list<std::int64_t> c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543};
|
||||
json j_flist(c_flist);
|
||||
|
||||
// create an array from std::array
|
||||
std::array<unsigned long, 4> c_array {{1, 2, 3, 4}};
|
||||
json j_array(c_array);
|
||||
|
||||
// create an array from std::set
|
||||
std::set<std::string> c_set {"one", "two", "three", "four", "one"};
|
||||
json j_set(c_set); // only one entry for "one" is used
|
||||
|
||||
// create an array from std::unordered_set
|
||||
std::unordered_set<std::string> c_uset {"one", "one"};
|
||||
json j_uset(c_uset); // only one entry for "one" is used
|
||||
|
||||
// create an array from std::multiset
|
||||
std::multiset<std::string> c_mset {"one", "two", "one", "four"};
|
||||
json j_mset(c_mset); // both entries for "one" are used
|
||||
|
||||
// create an array from std::unordered_multiset
|
||||
std::unordered_multiset<std::string> c_umset {"one", "one"};
|
||||
json j_umset(c_umset); // both entries for "one" are used
|
||||
|
||||
// serialize the JSON arrays
|
||||
std::cout << j_array_t << '\n';
|
||||
std::cout << j_vec << '\n';
|
||||
std::cout << j_valarray << '\n';
|
||||
std::cout << j_deque << '\n';
|
||||
std::cout << j_list << '\n';
|
||||
std::cout << j_flist << '\n';
|
||||
std::cout << j_array << '\n';
|
||||
std::cout << j_set << '\n';
|
||||
std::cout << j_uset << '\n';
|
||||
std::cout << j_mset << '\n';
|
||||
std::cout << j_umset << "\n\n";
|
||||
|
||||
// ============
|
||||
// string types
|
||||
// ============
|
||||
|
||||
// create string from a string_t value
|
||||
json::string_t string_value = "The quick brown fox jumps over the lazy dog.";
|
||||
json j_string_t(string_value);
|
||||
|
||||
// create a JSON string directly from a string literal
|
||||
json j_string_literal("The quick brown fox jumps over the lazy dog.");
|
||||
|
||||
// create string from std::string
|
||||
std::string s_stdstring = "The quick brown fox jumps over the lazy dog.";
|
||||
json j_stdstring(s_stdstring);
|
||||
|
||||
// serialize the JSON strings
|
||||
std::cout << j_string_t << '\n';
|
||||
std::cout << j_string_literal << '\n';
|
||||
std::cout << j_stdstring << "\n\n";
|
||||
|
||||
// ============
|
||||
// number types
|
||||
// ============
|
||||
|
||||
// create a JSON number from number_integer_t
|
||||
json::number_integer_t value_integer_t = -42;
|
||||
json j_integer_t(value_integer_t);
|
||||
|
||||
// create a JSON number from number_unsigned_t
|
||||
json::number_integer_t value_unsigned_t = 17;
|
||||
json j_unsigned_t(value_unsigned_t);
|
||||
|
||||
// create a JSON number from an anonymous enum
|
||||
enum { enum_value = 17 };
|
||||
json j_enum(enum_value);
|
||||
|
||||
// create values of different integer types
|
||||
short n_short = 42;
|
||||
int n_int = -23;
|
||||
long n_long = 1024;
|
||||
int_least32_t n_int_least32_t = -17;
|
||||
uint8_t n_uint8_t = 8;
|
||||
|
||||
// create (integer) JSON numbers
|
||||
json j_short(n_short);
|
||||
json j_int(n_int);
|
||||
json j_long(n_long);
|
||||
json j_int_least32_t(n_int_least32_t);
|
||||
json j_uint8_t(n_uint8_t);
|
||||
|
||||
// create values of different floating-point types
|
||||
json::number_float_t v_ok = 3.141592653589793;
|
||||
json::number_float_t v_nan = NAN;
|
||||
json::number_float_t v_infinity = INFINITY;
|
||||
|
||||
// create values of different floating-point types
|
||||
float n_float = 42.23;
|
||||
float n_float_nan = 1.0f / 0.0f;
|
||||
double n_double = 23.42;
|
||||
|
||||
// create (floating point) JSON numbers
|
||||
json j_ok(v_ok);
|
||||
json j_nan(v_nan);
|
||||
json j_infinity(v_infinity);
|
||||
json j_float(n_float);
|
||||
json j_float_nan(n_float_nan);
|
||||
json j_double(n_double);
|
||||
|
||||
// serialize the JSON numbers
|
||||
std::cout << j_integer_t << '\n';
|
||||
std::cout << j_unsigned_t << '\n';
|
||||
std::cout << j_enum << '\n';
|
||||
std::cout << j_short << '\n';
|
||||
std::cout << j_int << '\n';
|
||||
std::cout << j_long << '\n';
|
||||
std::cout << j_int_least32_t << '\n';
|
||||
std::cout << j_uint8_t << '\n';
|
||||
std::cout << j_ok << '\n';
|
||||
std::cout << j_nan << '\n';
|
||||
std::cout << j_infinity << '\n';
|
||||
std::cout << j_float << '\n';
|
||||
std::cout << j_float_nan << '\n';
|
||||
std::cout << j_double << "\n\n";
|
||||
|
||||
// =============
|
||||
// boolean types
|
||||
// =============
|
||||
|
||||
// create boolean values
|
||||
json j_truth = true;
|
||||
json j_falsity = false;
|
||||
|
||||
// serialize the JSON booleans
|
||||
std::cout << j_truth << '\n';
|
||||
std::cout << j_falsity << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__CompatibleType.output"
|
||||
{"one":1,"two":2}
|
||||
{"one":1,"three":3,"two":2}
|
||||
{"one":1.2,"three":3.4,"two":2.3}
|
||||
{"one":true,"three":false,"two":true}
|
||||
{"one":true,"three":false,"two":true}
|
||||
|
||||
["one","two",3,4.5,false]
|
||||
[1,2,3,4]
|
||||
[10,9,8,7]
|
||||
[1.2,2.3,3.4,5.6]
|
||||
[true,true,false,true]
|
||||
[12345678909876,23456789098765,34567890987654,45678909876543]
|
||||
[1,2,3,4]
|
||||
["four","one","three","two"]
|
||||
["one"]
|
||||
["four","one","one","two"]
|
||||
["one","one"]
|
||||
|
||||
"The quick brown fox jumps over the lazy dog."
|
||||
"The quick brown fox jumps over the lazy dog."
|
||||
"The quick brown fox jumps over the lazy dog."
|
||||
|
||||
-42
|
||||
17
|
||||
17
|
||||
42
|
||||
-23
|
||||
1024
|
||||
-17
|
||||
8
|
||||
3.141592653589793
|
||||
null
|
||||
null
|
||||
42.22999954223633
|
||||
null
|
||||
23.42
|
||||
|
||||
true
|
||||
false
|
||||
|
||||
```
|
||||
|
||||
Note the output is platform-dependent.
|
||||
@@ -382,13 +685,38 @@ basic_json(basic_json&& other) noexcept;
|
||||
converting to `json`, whose `object_t` sorts by key.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__BasicJsonType.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using ordered_json = nlohmann::ordered_json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create an ordered_json value; insertion order is preserved
|
||||
ordered_json oj = {{"c", 3}, {"a", 1}, {"b", 2}};
|
||||
|
||||
// convert to json -- overload (4) is used; keys end up sorted
|
||||
json j(oj);
|
||||
|
||||
// convert back to ordered_json -- the original insertion order is lost,
|
||||
// because it was already given up when converting to json
|
||||
ordered_json oj2(j);
|
||||
|
||||
std::cout << oj << '\n';
|
||||
std::cout << j << '\n';
|
||||
std::cout << oj2 << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__BasicJsonType.output"
|
||||
{"c":3,"a":1,"b":2}
|
||||
{"a":1,"b":2,"c":3}
|
||||
{"a":1,"b":2,"c":3}
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (5) create a container (array or object) from an initializer list"
|
||||
@@ -396,13 +724,39 @@ basic_json(basic_json&& other) noexcept;
|
||||
The example below shows how JSON values are created from initializer lists.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__list_init_t.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json j_empty_init_list = json({});
|
||||
json j_object = { {"one", 1}, {"two", 2} };
|
||||
json j_array = {1, 2, 3, 4};
|
||||
json j_nested_object = { {"one", {1}}, {"two", {1, 2}} };
|
||||
json j_nested_array = { {{1}, "one"}, {{1, 2}, "two"} };
|
||||
|
||||
// serialize the JSON value
|
||||
std::cout << j_empty_init_list << '\n';
|
||||
std::cout << j_object << '\n';
|
||||
std::cout << j_array << '\n';
|
||||
std::cout << j_nested_object << '\n';
|
||||
std::cout << j_nested_array << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__list_init_t.output"
|
||||
{}
|
||||
{"one":1,"two":2}
|
||||
[1,2,3,4]
|
||||
{"one":[1],"two":[1,2]}
|
||||
[[[1],"one"],[[1,2],"two"]]
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (6) construct an array with count copies of a given value"
|
||||
@@ -410,13 +764,34 @@ basic_json(basic_json&& other) noexcept;
|
||||
The following code shows examples for creating arrays with several copies of a given value.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__size_type_basic_json.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create an array by creating copies of a JSON value
|
||||
json value = "Hello";
|
||||
json array_0 = json(0, value);
|
||||
json array_1 = json(1, value);
|
||||
json array_5 = json(5, value);
|
||||
|
||||
// serialize the JSON arrays
|
||||
std::cout << array_0 << '\n';
|
||||
std::cout << array_1 << '\n';
|
||||
std::cout << array_5 << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__size_type_basic_json.output"
|
||||
[]
|
||||
["Hello"]
|
||||
["Hello","Hello","Hello","Hello","Hello"]
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (7) construct a JSON container given an iterator range"
|
||||
@@ -424,13 +799,49 @@ basic_json(basic_json&& other) noexcept;
|
||||
The example below shows several ways to create JSON values by specifying a subrange with iterators.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__InputIt_InputIt.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json j_array = {"alpha", "bravo", "charly", "delta", "easy"};
|
||||
json j_number = 42;
|
||||
json j_object = {{"one", "eins"}, {"two", "zwei"}};
|
||||
|
||||
// create copies using iterators
|
||||
json j_array_range(j_array.begin() + 1, j_array.end() - 2);
|
||||
json j_number_range(j_number.begin(), j_number.end());
|
||||
json j_object_range(j_object.begin(), j_object.find("two"));
|
||||
|
||||
// serialize the values
|
||||
std::cout << j_array_range << '\n';
|
||||
std::cout << j_number_range << '\n';
|
||||
std::cout << j_object_range << '\n';
|
||||
|
||||
// example for an exception
|
||||
try
|
||||
{
|
||||
json j_invalid(j_number.begin() + 1, j_number.end());
|
||||
}
|
||||
catch (const json::invalid_iterator& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__InputIt_InputIt.output"
|
||||
["bravo","charly"]
|
||||
42
|
||||
{"one":"eins"}
|
||||
[json.exception.invalid_iterator.204] iterators out of range
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (8) copy constructor"
|
||||
@@ -438,13 +849,32 @@ basic_json(basic_json&& other) noexcept;
|
||||
The following code shows an example for the copy constructor.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__basic_json.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON array
|
||||
json j1 = {"one", "two", 3, 4.5, false};
|
||||
|
||||
// create a copy
|
||||
json j2(j1);
|
||||
|
||||
// serialize the JSON array
|
||||
std::cout << j1 << " = " << j2 << '\n';
|
||||
std::cout << std::boolalpha << (j1 == j2) << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__basic_json.output"
|
||||
["one","two",3,4.5,false] = ["one","two",3,4.5,false]
|
||||
true
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (9) move constructor"
|
||||
@@ -452,13 +882,32 @@ basic_json(basic_json&& other) noexcept;
|
||||
The code below shows the move constructor explicitly called via `std::move`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/basic_json__moveconstructor.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
json a = 23;
|
||||
|
||||
// move contents of a to b
|
||||
json b(std::move(a));
|
||||
|
||||
// serialize the JSON arrays
|
||||
std::cout << a << '\n';
|
||||
std::cout << b << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/basic_json__moveconstructor.output"
|
||||
null
|
||||
23
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/basic_json/" rel="canonical"><link href=../ rel=prev><link href=../~basic_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>(Constructor) - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/basic_json/" rel="canonical"><link href=../ rel=prev><link href=../~basic_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>(Constructor) - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonbasic_json class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> (Constructor) </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Line truncated
|
||||
<span class=n>basic_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>value_t</span><span class=w> </span><span class=n>v</span><span class=p>);</span>
|
||||
|
||||
<span class=c1>// (2)</span>
|
||||
|
||||
+19
-2
@@ -28,13 +28,30 @@ Constant.
|
||||
The following code shows an example for `begin()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/begin.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create an array value
|
||||
json array = {1, 2, 3, 4, 5};
|
||||
|
||||
// get an iterator to the first element
|
||||
json::iterator it = array.begin();
|
||||
|
||||
// serialize the element that the iterator points to
|
||||
std::cout << *it << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/begin.output"
|
||||
1
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/begin/" rel="canonical"><link href=../back/ rel=prev><link href=../binary/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>begin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonbegin class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> begin </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div clLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/begin/" rel="canonical"><link href=../back/ rel=prev><link href=../binary/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>begin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonbegin class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> begin </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div clLine truncated
|
||||
<span class=n>const_iterator</span><span class=w> </span><span class=nf>begin</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
|
||||
</code></pre></div> <p>Returns an iterator to the first element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>begin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -52,13 +52,30 @@ initialization of a binary array type, for backwards compatibility and so it doe
|
||||
The following code shows how to create a binary value.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/binary.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a binary vector
|
||||
std::vector<std::uint8_t> vec = {0xCA, 0xFE, 0xBA, 0xBE};
|
||||
|
||||
// create a binary JSON value with subtype 42
|
||||
json j = json::binary(vec, 42);
|
||||
|
||||
// output type and subtype
|
||||
std::cout << "type: " << j.type_name() << ", subtype: " << j.get_binary().subtype() << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/binary.output"
|
||||
type: binary, subtype: 42
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/binary/" rel="canonical"><link href=../begin/ rel=prev><link href=../binary_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>binary - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonbinary class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/binary/" rel="canonical"><link href=../begin/ rel=prev><link href=../binary_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>binary - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> binary </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=nf>binary</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>binary_t</span><span class=o>::</span><span class=n>container_type</span><span class=o>&</span><span class=w> </span><span class=n>init</span><span class=p>);</span>
|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=nf>binary</span><span class=p>(</span><span class=k>typename</span><span class=w> </span><span class=nc>binary_t</span><span class=o>::</span><span class=n>container_type</span><span class=o>&&</span><span class=w> </span><span class=n>init</span><span class=p>);</span>
|
||||
|
||||
|
||||
@@ -106,13 +106,24 @@ type `#!cpp binary_t*` must be dereferenced.
|
||||
`#!cpp nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/binary_t.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
std::cout << std::boolalpha << std::is_same<nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>, json::binary_t>::value << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/binary_t.output"
|
||||
true
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/binary_t/" rel="canonical"><link href=../binary/ rel=prev><link href=../boolean_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>binary_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> binary_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/binary_t/" rel="canonical"><link href=../binary/ rel=prev><link href=../boolean_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>binary_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonbinary_t class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> binary_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg>Line truncated
|
||||
</code></pre></div> <p>This type is a type designed to carry binary data that appears in various serialized formats, such as <abbr title="Concise Binary Object Representation">CBOR</abbr>'s Major Type 2, MessagePack's bin, and <abbr title="Binary JSON">BSON</abbr>'s generic binary subtype. This type is NOT a part of standard <abbr title="JavaScript Object Notation">JSON</abbr> and exists solely for compatibility with these binary types. As such, it is simply defined as an ordered sequence of zero or more byte values.</p> <p>Additionally, as an implementation detail, the subtype of the binary data is carried around as a <code>std::uint64_t</code>, which is compatible with both of the binary data formats that use binary subtyping, (though the specific numbering is incompatible with each other, and it is up to the user to translate between them). The subtype is added to <code>BinaryType</code> via the helper type <a href=../../byte_container_with_subtype/ >byte_container_with_subtype</a>.</p> <p><a href="https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1"><abbr title="Concise Binary Object Representation">CBOR</abbr>'s <abbr title="Request for Comments">RFC</abbr> 8949</a> describes this type as:</p> <blockquote> <p>Major type 2: A byte string. The number of bytes in the string is equal to the argument.</p> </blockquote> <p><a href="https://github.com/msgpack/msgpack/blob/master/spec.md#bin-format-family">MessagePack's documentation on the bin type family</a> describes this type as:</p> <blockquote> <p>Bin format family stores a byte array in 2, 3, or 5 bytes of extra bytes in addition to the size of the byte array.</p> </blockquote> <p><a href="http://bsonspec.org/spec.html"><abbr title="Binary JSON">BSON</abbr>'s specifications</a> describe several binary types; however, this type is intended to represent the generic binary type which has the description:</p> <blockquote> <p>Generic binary subtype - This is the most commonly used binary subtype and should be the 'default' for drivers and tools.</p> </blockquote> <p>None of these impose any limitations on the internal representation other than the basic unit of storage be some type of array whose parts are decomposable into bytes.</p> <p>The default representation of this binary format is a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code>, which is a very common way to represent a byte array in modern C++.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>BinaryType</code></dt> <dd> <p>container type to store arrays</p> <p>Although not formally expressed as a C++ concept, <code>BinaryType</code> must be default-constructible, copy/move-constructible, and support <code>push_back()</code>, <code>.data()</code>, and <code>.size()</code>, because <a href=../../byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a> derives directly from it. Its <code>value_type</code> must additionally be exactly one byte wide (e.g., <code>std::uint8_t</code>/<code>char</code>/<code>std::byte</code>): the binary serializers (<abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, <abbr title="Binary JSON">BSON</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>) read and write the container's raw bytes via <code>reinterpret_cast</code>, which is only correct for byte-sized elements -- a container like <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>intptr_t</span><span class=o>></span></code> will not work as <code>BinaryType</code>. The elements must be stored contiguously, and the binary readers additionally require <code>resize()</code> and <code>operator[]</code>. See <a href=../../../features/types/template_parameters/#binarytype>Template Parameter Requirements</a> for the full list.</p> </dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>The default values for <code>BinaryType</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code>.</p> <h3 id=supported-byte-types>Supported byte types<a class=headerlink href=#supported-byte-types title="Permanent link">¶</a></h3> <p><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span clLine truncated
|
||||
|
||||
<span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>></span><span class=w> </span><span class=n>data</span><span class=p>{</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>1</span><span class=p>},</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>2</span><span class=p>},</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>3</span><span class=p>}};</span>
|
||||
|
||||
@@ -36,13 +36,24 @@ Boolean values are stored directly inside a `basic_json` type.
|
||||
The following code shows that `boolean_t` is by default, a typedef to `#!cpp bool`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/boolean_t.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
std::cout << std::boolalpha << std::is_same<bool, json::boolean_t>::value << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/boolean_t.output"
|
||||
true
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/boolean_t/" rel="canonical"><link href=../binary_t/ rel=prev><link href=../cbegin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>boolean_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> boolean_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/boolean_t/" rel="canonical"><link href=../binary_t/ rel=prev><link href=../cbegin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>boolean_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> boolean_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> booleans.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code class=highlight><span class=kc>true</span></code> and <code class=highlight><span class=kc>false</span></code>.</p> <p>To store boolean values in C++, a type is defined by the template parameter <code>BooleanType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>BooleanType</code></dt> <dd>the type to store booleans. As it is stored directly inside a <code>basic_json</code> value (in a union), it must be a trivially default-constructible, trivially copyable, and trivially destructible type that is convertible to and from <code class=highlight><span class=kt>bool</span></code>. See <a href=../../../features/types/template_parameters/#booleantype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>BooleanType</code> (<code class=highlight><span class=kt>bool</span></code>), the default value for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>boolean_t</code> is by default, a typedef to <code class=highlight><span class=kt>bool</span></code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -27,13 +27,30 @@ Constant.
|
||||
The following code shows an example for `cbegin()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/cbegin.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create an array value
|
||||
const json array = {1, 2, 3, 4, 5};
|
||||
|
||||
// get an iterator to the first element
|
||||
json::const_iterator it = array.cbegin();
|
||||
|
||||
// serialize the element that the iterator points to
|
||||
std::cout << *it << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/cbegin.output"
|
||||
1
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/cbegin/" rel="canonical"><link href=../boolean_t/ rel=prev><link href=../cbor_tag_handler_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>cbegin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncbegin class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> cbegin </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/cbegin/" rel="canonical"><link href=../boolean_t/ rel=prev><link href=../cbor_tag_handler_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>cbegin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncbegin class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> cbegin </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></Line truncated
|
||||
</code></pre></div> <p>Returns an iterator to the first element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cbegin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
|
||||
@@ -29,13 +29,44 @@ store
|
||||
[`from_cbor`](from_cbor.md) when reading a tagged byte string.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/cbor_tag_handler_t.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// tagged byte string
|
||||
std::vector<std::uint8_t> vec = {{0xd8, 0x42, 0x44, 0xcA, 0xfe, 0xba, 0xbe}};
|
||||
|
||||
// cbor_tag_handler_t::error throws
|
||||
try
|
||||
{
|
||||
auto b_throw_on_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::error);
|
||||
}
|
||||
catch (const json::parse_error& e)
|
||||
{
|
||||
std::cout << e.what() << std::endl;
|
||||
}
|
||||
|
||||
// cbor_tag_handler_t::ignore ignores the tag
|
||||
auto b_ignore_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::ignore);
|
||||
std::cout << b_ignore_tag << std::endl;
|
||||
|
||||
// cbor_tag_handler_t::store stores the tag as binary subtype
|
||||
auto b_store_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::store);
|
||||
std::cout << b_store_tag << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/cbor_tag_handler_t.output"
|
||||
[json.exception.parse_error.112] parse error at byte 1: syntax error while parsing CBOR value: invalid byte: 0xD8
|
||||
{"bytes":[202,254,186,190],"subtype":null}
|
||||
{"bytes":[202,254,186,190],"subtype":66}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/cbor_tag_handler_t/" rel="canonical"><link href=../cbegin/ rel=prev><link href=../cend/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>cbor_tag_handler_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncbor_tag_handler_t class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> cbor_tag_handler_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> cbor_tag_handler_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
||||
<span class=p>{</span>
|
||||
<span class=w> </span><span class=n>error</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=n>ignore</span><span class=p>,</span>
|
||||
|
||||
+22
-2
@@ -27,13 +27,33 @@ Constant.
|
||||
The following code shows an example for `cend()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/cend.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create an array value
|
||||
json array = {1, 2, 3, 4, 5};
|
||||
|
||||
// get an iterator to one past the last element
|
||||
json::const_iterator it = array.cend();
|
||||
|
||||
// decrement the iterator to point to the last element
|
||||
--it;
|
||||
|
||||
// serialize the element that the iterator points to
|
||||
std::cout << *it << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/cend.output"
|
||||
5
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/cend/" rel="canonical"><link href=../cbor_tag_handler_t/ rel=prev><link href=../clear/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>cend - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> cend </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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|
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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> cend </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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|
||||
</code></pre></div> <p>Returns an iterator to one past the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cend()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
|
||||
+43
-2
@@ -43,13 +43,54 @@ All iterators, pointers, and references related to this container are invalidate
|
||||
JSON types.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/clear.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json j_null;
|
||||
json j_boolean = true;
|
||||
json j_number_integer = 17;
|
||||
json j_number_float = 23.42;
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
json j_array = {1, 2, 4, 8, 16};
|
||||
json j_string = "Hello, world";
|
||||
|
||||
// call clear()
|
||||
j_null.clear();
|
||||
j_boolean.clear();
|
||||
j_number_integer.clear();
|
||||
j_number_float.clear();
|
||||
j_object.clear();
|
||||
j_array.clear();
|
||||
j_string.clear();
|
||||
|
||||
// serialize the cleared values()
|
||||
std::cout << j_null << '\n';
|
||||
std::cout << j_boolean << '\n';
|
||||
std::cout << j_number_integer << '\n';
|
||||
std::cout << j_number_float << '\n';
|
||||
std::cout << j_object << '\n';
|
||||
std::cout << j_array << '\n';
|
||||
std::cout << j_string << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/clear.output"
|
||||
null
|
||||
false
|
||||
0
|
||||
0.0
|
||||
{}
|
||||
[]
|
||||
""
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/clear/" rel="canonical"><link href=../cend/ rel=prev><link href=../contains/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>clear - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonclear class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> clear </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/clear/" rel="canonical"><link href=../cend/ rel=prev><link href=../contains/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>clear - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonclear class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> clear </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div Line truncated
|
||||
</code></pre></div> <p>Clears the content of a <abbr title="JavaScript Object Notation">JSON</abbr> value and resets it to the default value as if <a href=../basic_json/ ><code>basic_json(value_t)</code></a> would have been called with the current value type from <a href=../type/ ><code>type()</code></a>:</p> <table> <thead> <tr> <th>Value type</th> <th>initial value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code>null</code></td> </tr> <tr> <td>boolean</td> <td><code>false</code></td> </tr> <tr> <td>string</td> <td><code>""</code></td> </tr> <tr> <td>number</td> <td><code>0</code></td> </tr> <tr> <td>binary</td> <td>An empty byte vector with no subtype</td> </tr> <tr> <td>object</td> <td><code>{}</code></td> </tr> <tr> <td>array</td> <td><code>[]</code></td> </tr> </tbody> </table> <p>Has the same effect as calling</p> <div class=highlight><pre><span></span><code><span class=o>*</span><span class=k>this</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>basic_json</span><span class=p>(</span><span class=n>type</span><span class=p>());</span>
|
||||
</code></pre></div> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>All iterators, pointers, and references related to this container are invalidated.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows the effect of <code>clear()</code> to different <abbr title="JavaScript Object Notation">JSON</abbr> types.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -10,6 +10,10 @@ bool contains(KeyType&& key) const;
|
||||
|
||||
// (3)
|
||||
bool contains(const json_pointer& ptr) const;
|
||||
|
||||
// (4)
|
||||
template<typename T>
|
||||
bool contains(T) const = delete;
|
||||
```
|
||||
|
||||
1. Check whether an element exists in a JSON object with a key equivalent to `key`. If the element is not found or the
|
||||
@@ -17,6 +21,9 @@ bool contains(const json_pointer& ptr) const;
|
||||
2. See 1. This overload is only available if `KeyType` is comparable with `#!cpp typename object_t::key_type` and
|
||||
`#!cpp typename object_comparator_t::is_transparent` denotes a type.
|
||||
3. Check whether the given JSON pointer `ptr` can be resolved in the current JSON value.
|
||||
4. Deleted: this overload is only available if `T` is an integral type and is declared as deleted, so that a call with
|
||||
an integer `key` (for example, `#!cpp j.contains(0)`) fails to compile. Otherwise, the integer literal `0` would convert to
|
||||
a null `#!cpp const char*` and, from there, to the key type, causing undefined behavior at runtime.
|
||||
|
||||
## Template parameters
|
||||
|
||||
@@ -39,6 +46,7 @@ bool contains(const json_pointer& ptr) const;
|
||||
is not an object, `#!cpp false` is returned.
|
||||
2. See 1.
|
||||
3. `#!cpp true` if the JSON pointer can be resolved to a stored value, `#!cpp false` otherwise.
|
||||
4. Deleted; a call with an integral argument does not compile.
|
||||
|
||||
## Exception safety
|
||||
|
||||
@@ -49,6 +57,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
1. The function does not throw exceptions.
|
||||
2. The function does not throw exceptions.
|
||||
3. The function does not throw exceptions.
|
||||
4. Deleted; a call with an integral argument does not compile.
|
||||
|
||||
## Complexity
|
||||
|
||||
@@ -86,13 +95,34 @@ Logarithmic in the size of the JSON object.
|
||||
The example shows how `contains()` is used.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/contains__object_t_key_type.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create some JSON values
|
||||
json j_object = R"( {"key": "value"} )"_json;
|
||||
json j_array = R"( [1, 2, 3] )"_json;
|
||||
|
||||
// call contains
|
||||
std::cout << std::boolalpha <<
|
||||
"j_object contains 'key': " << j_object.contains("key") << '\n' <<
|
||||
"j_object contains 'another': " << j_object.contains("another") << '\n' <<
|
||||
"j_array contains 'key': " << j_array.contains("key") << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/contains__object_t_key_type.output"
|
||||
j_object contains 'key': true
|
||||
j_object contains 'another': false
|
||||
j_array contains 'key': false
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) check with key using string_view"
|
||||
@@ -100,13 +130,36 @@ Logarithmic in the size of the JSON object.
|
||||
The example shows how `contains()` is used.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/contains__keytype.c++17.cpp"
|
||||
#include <iostream>
|
||||
#include <string_view>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using namespace std::string_view_literals;
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create some JSON values
|
||||
json j_object = R"( {"key": "value"} )"_json;
|
||||
json j_array = R"( [1, 2, 3] )"_json;
|
||||
|
||||
// call contains
|
||||
std::cout << std::boolalpha <<
|
||||
"j_object contains 'key': " << j_object.contains("key"sv) << '\n' <<
|
||||
"j_object contains 'another': " << j_object.contains("another"sv) << '\n' <<
|
||||
"j_array contains 'key': " << j_array.contains("key"sv) << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/contains__keytype.c++17.output"
|
||||
j_object contains 'key': true
|
||||
j_object contains 'another': false
|
||||
j_array contains 'key': false
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (3) check with JSON pointer"
|
||||
@@ -114,13 +167,49 @@ Logarithmic in the size of the JSON object.
|
||||
The example shows how `contains()` is used.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/contains__json_pointer.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
json j =
|
||||
{
|
||||
{"number", 1}, {"string", "foo"}, {"array", {1, 2}}
|
||||
};
|
||||
|
||||
std::cout << std::boolalpha
|
||||
<< j.contains("/number"_json_pointer) << '\n'
|
||||
<< j.contains("/string"_json_pointer) << '\n'
|
||||
<< j.contains("/array"_json_pointer) << '\n'
|
||||
<< j.contains("/array/1"_json_pointer) << '\n'
|
||||
<< j.contains("/array/-"_json_pointer) << '\n'
|
||||
<< j.contains("/array/4"_json_pointer) << '\n'
|
||||
<< j.contains("/baz"_json_pointer) << '\n'
|
||||
// an array index with a leading '0' is not found
|
||||
<< j.contains("/array/01"_json_pointer) << '\n'
|
||||
// an array index that is not a number is not found
|
||||
<< j.contains("/array/one"_json_pointer) << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/contains__json_pointer.output"
|
||||
true
|
||||
true
|
||||
true
|
||||
true
|
||||
false
|
||||
false
|
||||
false
|
||||
false
|
||||
false
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/contains/" rel="canonical"><link href=../clear/ rel=prev><link href=../count/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>contains - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncontains class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> contains </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </laLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/contains/" rel="canonical"><link href=../clear/ rel=prev><link href=../count/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>contains - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncontains class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> contains </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </laLine truncated
|
||||
<span class=kt>bool</span><span class=w> </span><span class=nf>contains</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
|
||||
<span class=c1>// (2)</span>
|
||||
@@ -7,7 +7,11 @@
|
||||
|
||||
<span class=c1>// (3)</span>
|
||||
<span class=kt>bool</span><span class=w> </span><span class=nf>contains</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json_pointer</span><span class=o>&</span><span class=w> </span><span class=n>ptr</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
</code></pre></div> <ol> <li>Check whether an element exists in a <abbr title="JavaScript Object Notation">JSON</abbr> object with a key equivalent to <code>key</code>. If the element is not found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code class=highlight><span class=nb>false</span></code> is returned.</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Check whether the given <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> can be resolved in the current <abbr title="JavaScript Object Notation">JSON</abbr> value.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value to check its existence.</dd> <dt><code>ptr</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> pointer to check its existence.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <ol> <li><code class=highlight><span class=nb>true</span></code> if an element with specified <code>key</code> exists. If no such element with such a key is found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code class=highlight><span class=nb>false</span></code> is returned.</li> <li>See 1.</li> <li><code class=highlight><span class=nb>true</span></code> if the <abbr title="JavaScript Object Notation">JSON</abbr> pointer can be resolved to a stored value, <code class=highlight><span class=nb>false</span></code> otherwise.</li> </ol> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <ol> <li>The function does not throw exceptions.</li> <li>The function does not throw exceptions.</li> <li>The function does not throw exceptions.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <ul> <li>This method always returns <code class=highlight><span class=nb>false</span></code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>This method can be executed on any <abbr title="JavaScript Object Notation">JSON</abbr> value type.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>contains</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To check for an array element instead, use <a href=../at/ ><code>at</code></a>, <a href=../operator%5B%5D/ ><code>operator[]</code></a>, or compare against <a href=../size/ ><code>size</code></a>.</li> </ul> <div class="admonition info"> <p class=admonition-title>Postconditions</p> <p>If <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=n>x</span><span class=p>)</span></code> returns <code class=highlight><span class=nb>true</span></code> for a key or <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>x</code>, then it is safe to call <code>j[x]</code>.</p> </div> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <p>Overload (3) also accepts a <a href=../../json_pointer/ ><code>json_pointer</code></a> whose template argument iLine truncated
|
||||
|
||||
<span class=c1>// (4)</span>
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=o>></span>
|
||||
<span class=kt>bool</span><span class=w> </span><span class=n>contains</span><span class=p>(</span><span class=n>T</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>delete</span><span class=p>;</span>
|
||||
</code></pre></div> <ol> <li>Check whether an element exists in a <abbr title="JavaScript Object Notation">JSON</abbr> object with a key equivalent to <code>key</code>. If the element is not found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code class=highlight><span class=nb>false</span></code> is returned.</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Check whether the given <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> can be resolved in the current <abbr title="JavaScript Object Notation">JSON</abbr> value.</li> <li>Deleted: this overload is only available if <code>T</code> is an integral type and is declared as deleted, so that a call with an integer <code>key</code> (for example, <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) fails to compile. Otherwise, the integer literal <code>0</code> would convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, to the key type, causing undefined behavior at runtime.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value to check its existence.</dd> <dt><code>ptr</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> pointer to check its existence.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <ol> <li><code class=highlight><span class=nb>true</span></code> if an element with specified <code>key</code> exists. If no such element with such a key is found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code class=highlight><span class=nb>false</span></code> is returned.</li> <li>See 1.</li> <li><code class=highlight><span class=nb>true</span></code> if the <abbr title="JavaScript Object Notation">JSON</abbr> pointer can be resolved to a stored value, <code class=highlight><span class=nb>false</span></code> otherwise.</li> <li>Deleted; a call with an integral argument does not compile.</li> </ol> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <ol> <li>The function does not throw exceptions.</li> <li>The function does not throw exceptions.</li> <li>The function does not throw exceptions.</li> <li>Deleted; a call with an integral argument does not compile.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <ul> <li>This method always returns <code class=highlight><span class=nb>false</span></code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>This method can be executed on any <abbr title="JavaScript Object Notation">JSON</abbr> value type.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>contains</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To check for an array element instead, use <a href=../at/ ><code>at</code></a>, <aLine truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
@@ -87,4 +91,4 @@
|
||||
<span class=kc>false</span>
|
||||
<span class=kc>false</span>
|
||||
<span class=kc>false</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../find/ >find</a> find a value in an object</li> <li><a href=../count/ >count</a> returns the number of occurrences of a key</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 3.6.0. Extended template <code>KeyType</code> to support comparable types in version 3.11.0. Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to consistently accept <code>std::string_view</code>-convertible keys, as already supported by <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../value/ ><code>value</code></a>, and other lookup functions.</li> <li>Added in version 3.7.0.</li> <li>Deleted overloads for integral key types added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 09:46:32 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontaLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../find/ >find</a> find a value in an object</li> <li><a href=../count/ >count</a> returns the number of occurrences of a key</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 3.6.0. Extended template <code>KeyType</code> to support comparable types in version 3.11.0. Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to consistently accept <code>std::string_view</code>-convertible keys, as already supported by <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../value/ ><code>value</code></a>, and other lookup functions.</li> <li>Added in version 3.7.0.</li> <li>Deleted overloads for integral key types added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fonLine truncated
|
||||
@@ -10,11 +10,16 @@ bool contains(KeyType&& key) const;
|
||||
|
||||
// (3)
|
||||
bool contains(const json_pointer& ptr) const;
|
||||
|
||||
// (4)
|
||||
template<typename T>
|
||||
bool contains(T) const = delete;
|
||||
```
|
||||
|
||||
1. Check whether an element exists in a JSON object with a key equivalent to `key`. If the element is not found or the JSON value is not an object, `false` is returned.
|
||||
1. See 1. This overload is only available if `KeyType` is comparable with `typename object_t::key_type` and `typename object_comparator_t::is_transparent` denotes a type.
|
||||
1. Check whether the given JSON pointer `ptr` can be resolved in the current JSON value.
|
||||
1. Deleted: this overload is only available if `T` is an integral type and is declared as deleted, so that a call with an integer `key` (for example, `j.contains(0)`) fails to compile. Otherwise, the integer literal `0` would convert to a null `const char*` and, from there, to the key type, causing undefined behavior at runtime.
|
||||
|
||||
## Template parameters
|
||||
|
||||
@@ -31,6 +36,7 @@ bool contains(const json_pointer& ptr) const;
|
||||
1. `true` if an element with specified `key` exists. If no such element with such a key is found or the JSON value is not an object, `false` is returned.
|
||||
1. See 1.
|
||||
1. `true` if the JSON pointer can be resolved to a stored value, `false` otherwise.
|
||||
1. Deleted; a call with an integral argument does not compile.
|
||||
|
||||
## Exception safety
|
||||
|
||||
@@ -41,6 +47,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
1. The function does not throw exceptions.
|
||||
1. The function does not throw exceptions.
|
||||
1. The function does not throw exceptions.
|
||||
1. Deleted; a call with an integral argument does not compile.
|
||||
|
||||
## Complexity
|
||||
|
||||
|
||||
+53
-4
@@ -7,12 +7,19 @@ size_type count(const typename object_t::key_type& key) const;
|
||||
// (2)
|
||||
template<typename KeyType>
|
||||
size_type count(KeyType&& key) const;
|
||||
|
||||
// (3)
|
||||
template<typename T>
|
||||
size_type count(T) const = delete;
|
||||
```
|
||||
|
||||
1. Returns the number of elements with key `key`. If `ObjectType` is the default `std::map` type, the return value will
|
||||
always be `0` (`key` was not found) or `1` (`key` was found).
|
||||
2. See 1. This overload is only available if `KeyType` is comparable with `#!cpp typename object_t::key_type` and
|
||||
`#!cpp typename object_comparator_t::is_transparent` denotes a type.
|
||||
3. Deleted: this overload is only available if `T` is an integral type and is declared as deleted, so that a call with
|
||||
an integer `key` (for example, `#!cpp j.count(0)`) fails to compile. Otherwise, the integer literal `0` would convert to
|
||||
a null `#!cpp const char*` and, from there, to the key type, causing undefined behavior at runtime.
|
||||
|
||||
## Template parameters
|
||||
|
||||
@@ -53,13 +60,33 @@ Logarithmic in the size of the JSON object.
|
||||
The example shows how `count()` is used.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/count__object_t_key_type.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON object
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
|
||||
// call count()
|
||||
auto count_two = j_object.count("two");
|
||||
auto count_three = j_object.count("three");
|
||||
|
||||
// print values
|
||||
std::cout << "number of elements with key \"two\": " << count_two << '\n';
|
||||
std::cout << "number of elements with key \"three\": " << count_three << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/count__object_t_key_type.output"
|
||||
number of elements with key "two": 1
|
||||
number of elements with key "three": 0
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) count number of elements using string_view"
|
||||
@@ -67,13 +94,35 @@ Logarithmic in the size of the JSON object.
|
||||
The example shows how `count()` is used.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/count__keytype.c++17.cpp"
|
||||
#include <iostream>
|
||||
#include <string_view>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using namespace std::string_view_literals;
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON object
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
|
||||
// call count()
|
||||
auto count_two = j_object.count("two"sv);
|
||||
auto count_three = j_object.count("three"sv);
|
||||
|
||||
// print values
|
||||
std::cout << "number of elements with key \"two\": " << count_two << '\n';
|
||||
std::cout << "number of elements with key \"three\": " << count_three << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/count__keytype.c++17.output"
|
||||
number of elements with key "two": 1
|
||||
number of elements with key "three": 0
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,10 +1,14 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/count/" rel="canonical"><link href=../contains/ rel=prev><link href=../crbegin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>count - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncount class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> count </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <dLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/count/" rel="canonical"><link href=../contains/ rel=prev><link href=../crbegin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>count - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncount class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> count </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <dLine truncated
|
||||
<span class=n>size_type</span><span class=w> </span><span class=nf>count</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
|
||||
<span class=c1>// (2)</span>
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>KeyType</span><span class=o>></span>
|
||||
<span class=n>size_type</span><span class=w> </span><span class=n>count</span><span class=p>(</span><span class=n>KeyType</span><span class=o>&&</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
</code></pre></div> <ol> <li>Returns the number of elements with key <code>key</code>. If <code>ObjectType</code> is the default <code>std::map</code> type, the return value will always be <code>0</code> (<code>key</code> was not found) or <code>1</code> (<code>key</code> was found).</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value of the element to count.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>Number of elements with key <code>key</code>. If the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, the return value will be <code>0</code>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <ul> <li>This method always returns <code>0</code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>count</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To check for an array element instead, use <a href=../at/ ><code>at</code></a>, <a href=../operator%5B%5D/ ><code>operator[]</code></a>, or compare against <a href=../size/ ><code>size</code></a>.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: (1) count number of elements</summary> <p>The example shows how <code>count()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
|
||||
<span class=c1>// (3)</span>
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=o>></span>
|
||||
<span class=n>size_type</span><span class=w> </span><span class=n>count</span><span class=p>(</span><span class=n>T</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>delete</span><span class=p>;</span>
|
||||
</code></pre></div> <ol> <li>Returns the number of elements with key <code>key</code>. If <code>ObjectType</code> is the default <code>std::map</code> type, the return value will always be <code>0</code> (<code>key</code> was not found) or <code>1</code> (<code>key</code> was found).</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Deleted: this overload is only available if <code>T</code> is an integral type and is declared as deleted, so that a call with an integer <code>key</code> (for example, <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>count</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) fails to compile. Otherwise, the integer literal <code>0</code> would convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, to the key type, causing undefined behavior at runtime.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value of the element to count.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>Number of elements with key <code>key</code>. If the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, the return value will be <code>0</code>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <ul> <li>This method always returns <code>0</code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>count</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To check for an array element instead, use <a href=../at/ ><code>at</code></a>, <a href=../operator%5B%5D/ ><code>operator[]</code></a>, or compare against <a href=../size/ ><code>size</code></a>.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: (1) count number of elements</summary> <p>The example shows how <code>count()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
@@ -46,4 +50,4 @@
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>nu</span><span class=err>mber</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>eleme</span><span class=kc>nts</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=nt>"two"</span><span class=p>:</span><span class=w> </span><span class=mi>1</span>
|
||||
<span class=kc>nu</span><span class=err>mber</span><span class=w> </span><span class=err>o</span><span class=kc>f</span><span class=w> </span><span class=err>eleme</span><span class=kc>nts</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=nt>"three"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../find/ >find</a> find a value in an object</li> <li><a href=../contains/ >contains</a> checks whether a key exists</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 1.0.0. Changed parameter <code>key</code> type to <code>KeyType&&</code> in version 3.11.0. Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to consistently accept <code>std::string_view</code>-convertible keys, as already supported by <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../value/ ><code>value</code></a>, and other lookup functions.</li> <li>Deleted overload for integral key types added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 09:46:32 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontaweLine truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../find/ >find</a> find a value in an object</li> <li><a href=../contains/ >contains</a> checks whether a key exists</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 1.0.0. Changed parameter <code>key</code> type to <code>KeyType&&</code> in version 3.11.0. Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to consistently accept <code>std::string_view</code>-convertible keys, as already supported by <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../value/ ><code>value</code></a>, and other lookup functions.</li> <li>Deleted overload for integral key types added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontaLine truncated
|
||||
@@ -7,10 +7,15 @@ size_type count(const typename object_t::key_type& key) const;
|
||||
// (2)
|
||||
template<typename KeyType>
|
||||
size_type count(KeyType&& key) const;
|
||||
|
||||
// (3)
|
||||
template<typename T>
|
||||
size_type count(T) const = delete;
|
||||
```
|
||||
|
||||
1. Returns the number of elements with key `key`. If `ObjectType` is the default `std::map` type, the return value will always be `0` (`key` was not found) or `1` (`key` was found).
|
||||
1. See 1. This overload is only available if `KeyType` is comparable with `typename object_t::key_type` and `typename object_comparator_t::is_transparent` denotes a type.
|
||||
1. Deleted: this overload is only available if `T` is an integral type and is declared as deleted, so that a call with an integer `key` (for example, `j.count(0)`) fails to compile. Otherwise, the integer literal `0` would convert to a null `const char*` and, from there, to the key type, causing undefined behavior at runtime.
|
||||
|
||||
## Template parameters
|
||||
|
||||
|
||||
@@ -27,13 +27,30 @@ Constant.
|
||||
The following code shows an example for `crbegin()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/crbegin.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create an array value
|
||||
json array = {1, 2, 3, 4, 5};
|
||||
|
||||
// get an iterator to the reverse-beginning
|
||||
json::const_reverse_iterator it = array.crbegin();
|
||||
|
||||
// serialize the element that the iterator points to
|
||||
std::cout << *it << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/crbegin.output"
|
||||
5
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/crbegin/" rel="canonical"><link href=../count/ rel=prev><link href=../crend/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>crbegin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> crbegin </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label>Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/crbegin/" rel="canonical"><link href=../count/ rel=prev><link href=../crend/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>crbegin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncrbegin class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> crbegin </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label>Line truncated
|
||||
</code></pre></div> <p>Returns an iterator to the reverse-beginning; that is, the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-rbegin-rend.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>reverse iterator to the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>crbegin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
|
||||
+22
-2
@@ -28,13 +28,33 @@ Constant.
|
||||
The following code shows an example for `crend()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/crend.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create an array value
|
||||
json array = {1, 2, 3, 4, 5};
|
||||
|
||||
// get an iterator to the reverse-end
|
||||
json::const_reverse_iterator it = array.crend();
|
||||
|
||||
// increment the iterator to point to the first element
|
||||
--it;
|
||||
|
||||
// serialize the element that the iterator points to
|
||||
std::cout << *it << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/crend.output"
|
||||
1
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/crend/" rel="canonical"><link href=../crbegin/ rel=prev><link href=../default_object_comparator_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>crend - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncrend class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> crend </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/crend/" rel="canonical"><link href=../crbegin/ rel=prev><link href=../default_object_comparator_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>crend - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsoncrend class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> crend </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/Line truncated
|
||||
</code></pre></div> <p>Returns an iterator to the reverse-end; that is, one before the first element. This element acts as a placeholder, attempting to access it results in undefined behavior.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-rbegin-rend.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>reverse iterator to the element following the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>crend()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
|
||||
@@ -21,13 +21,26 @@ The actual comparator used depends on [`object_t`](object_t.md) and can be obtai
|
||||
The example below demonstrates the default comparator.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/default_object_comparator_t.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
std::cout << std::boolalpha
|
||||
<< "one < two : " << json::default_object_comparator_t{}("one", "two") << "\n"
|
||||
<< "three < four : " << json::default_object_comparator_t{}("three", "four") << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/default_object_comparator_t.output"
|
||||
one < two : true
|
||||
three < four : false
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/default_object_comparator_t/" rel="canonical"><link href=../crend/ rel=prev><link href=../diff/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>default_object_comparator_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/default_object_comparator_t/" rel="canonical"><link href=../crend/ rel=prev><link href=../diff/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>default_object_comparator_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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|
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|
||||
<span class=k>using</span><span class=w> </span><span class=n>default_object_comparator_t</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>less</span><span class=o><></span><span class=p>;</span><span class=w> </span><span class=c1>// since C++14</span>
|
||||
</code></pre></div> <p>The default comparator used by <a href=../object_t/ ><code>object_t</code></a>.</p> <p>Since C++14 a transparent comparator is used which prevents unnecessary string construction when looking up a key in an object.</p> <p>The actual comparator used depends on <a href=../object_t/ ><code>object_t</code></a> and can be obtained via <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example below demonstrates the default comparator.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
|
||||
+65
-2
@@ -44,13 +44,75 @@ Currently, only `remove`, `add`, and `replace` operations are generated.
|
||||
The following code shows how a JSON patch is created as a diff for two JSON values.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/diff.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
int main()
|
||||
{
|
||||
// the source document
|
||||
json source = R"(
|
||||
{
|
||||
"baz": "qux",
|
||||
"foo": "bar"
|
||||
}
|
||||
)"_json;
|
||||
|
||||
// the target document
|
||||
json target = R"(
|
||||
{
|
||||
"baz": "boo",
|
||||
"hello": [
|
||||
"world"
|
||||
]
|
||||
}
|
||||
)"_json;
|
||||
|
||||
// create the patch
|
||||
json patch = json::diff(source, target);
|
||||
|
||||
// roundtrip
|
||||
json patched_source = source.patch(patch);
|
||||
|
||||
// output patch and roundtrip result
|
||||
std::cout << std::setw(4) << patch << "\n\n"
|
||||
<< std::setw(4) << patched_source << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/diff.output"
|
||||
[
|
||||
{
|
||||
"op": "replace",
|
||||
"path": "/baz",
|
||||
"value": "boo"
|
||||
},
|
||||
{
|
||||
"op": "remove",
|
||||
"path": "/foo"
|
||||
},
|
||||
{
|
||||
"op": "add",
|
||||
"path": "/hello",
|
||||
"value": [
|
||||
"world"
|
||||
]
|
||||
}
|
||||
]
|
||||
|
||||
{
|
||||
"baz": "boo",
|
||||
"hello": [
|
||||
"world"
|
||||
]
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -59,6 +121,7 @@ Currently, only `remove`, `add`, and `replace` operations are generated.
|
||||
- [patch](patch.md) applies a JSON Patch
|
||||
- [patch_inplace](patch_inplace.md) applies a JSON Patch in place
|
||||
- [merge_patch](merge_patch.md) applies a JSON Merge Patch
|
||||
- [merge_diff](merge_diff.md) creates a diff as a JSON Merge Patch
|
||||
|
||||
## Version history
|
||||
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/diff/" rel="canonical"><link href=../default_object_comparator_t/ rel=prev><link href=../dump/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>diff - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> diff </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg>Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/diff/" rel="canonical"><link href=../default_object_comparator_t/ rel=prev><link href=../dump/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>diff - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> diff </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg>Line truncated
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<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json</span><span class=o>&</span><span class=w> </span><span class=n>target</span><span class=p>);</span>
|
||||
</code></pre></div> <p>Creates a <a href="http://jsonpatch.com"><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a> so that value <code>source</code> can be changed into the value <code>target</code> by calling <a href=../patch/ ><code>patch</code></a> function.</p> <p>For two <abbr title="JavaScript Object Notation">JSON</abbr> values <code>source</code> and <code>target</code>, the following code always yields <code class=highlight><span class=nb>true</span></code>: <div class=highlight><pre><span></span><code><span class=n>source</span><span class=p>.</span><span class=n>patch</span><span class=p>(</span><span class=n>diff</span><span class=p>(</span><span class=n>source</span><span class=p>,</span><span class=w> </span><span class=n>target</span><span class=p>))</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>target</span><span class=p>;</span>
|
||||
</code></pre></div></p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>source</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to compare from</dd> <dt><code>target</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to compare against</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>a <abbr title="JavaScript Object Notation">JSON</abbr> patch to convert the <code>source</code> to <code>target</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: <code>source</code> and <code>target</code> are never modified.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the lengths of <code>source</code> and <code>target</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Currently, only <code>remove</code>, <code>add</code>, and <code>replace</code> operations are generated.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how a <abbr title="JavaScript Object Notation">JSON</abbr> patch is created as a diff for two <abbr title="JavaScript Object Notation">JSON</abbr> values.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
@@ -63,4 +63,4 @@
|
||||
<span class=w> </span><span class=s2>"world"</span>
|
||||
<span class=w> </span><span class=p>]</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a></li> <li><a href=../patch/ >patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> <li><a href=../patch_inplace/ >patch_inplace</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch in place</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 16:20:20 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V41Line truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a></li> <li><a href=../patch/ >patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> <li><a href=../patch_inplace/ >patch_inplace</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch in place</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../merge_diff/ >merge_diff</a> creates a diff as a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 12, 2026 07:33:43 UTC">October 12, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.Line truncated
|
||||
@@ -117,6 +117,7 @@ Output:
|
||||
- [patch](https://json.nlohmann.me/api/basic_json/patch/index.md) applies a JSON Patch
|
||||
- [patch_inplace](https://json.nlohmann.me/api/basic_json/patch_inplace/index.md) applies a JSON Patch in place
|
||||
- [merge_patch](https://json.nlohmann.me/api/basic_json/merge_patch/index.md) applies a JSON Merge Patch
|
||||
- [merge_diff](https://json.nlohmann.me/api/basic_json/merge_diff/index.md) creates a diff as a JSON Merge Patch
|
||||
|
||||
## Version history
|
||||
|
||||
|
||||
+105
-2
@@ -75,13 +75,116 @@ Binary values are serialized as an object containing two keys:
|
||||
result of the serialization.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/dump.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
json j_array = {1, 2, 4, 8, 16};
|
||||
json j_string = "Hellö 😀!";
|
||||
|
||||
// call dump()
|
||||
std::cout << "objects:" << '\n'
|
||||
<< j_object.dump() << "\n\n"
|
||||
<< j_object.dump(-1) << "\n\n"
|
||||
<< j_object.dump(0) << "\n\n"
|
||||
<< j_object.dump(4) << "\n\n"
|
||||
<< j_object.dump(1, '\t') << "\n\n";
|
||||
|
||||
std::cout << "arrays:" << '\n'
|
||||
<< j_array.dump() << "\n\n"
|
||||
<< j_array.dump(-1) << "\n\n"
|
||||
<< j_array.dump(0) << "\n\n"
|
||||
<< j_array.dump(4) << "\n\n"
|
||||
<< j_array.dump(1, '\t') << "\n\n";
|
||||
|
||||
std::cout << "strings:" << '\n'
|
||||
<< j_string.dump() << '\n'
|
||||
<< j_string.dump(-1, ' ', true) << '\n';
|
||||
|
||||
// create JSON value with invalid UTF-8 byte sequence
|
||||
json j_invalid = "ä\xA9ü";
|
||||
try
|
||||
{
|
||||
std::cout << j_invalid.dump() << std::endl;
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << std::endl;
|
||||
}
|
||||
|
||||
std::cout << "string with replaced invalid characters: "
|
||||
<< j_invalid.dump(-1, ' ', false, json::error_handler_t::replace)
|
||||
<< "\nstring with ignored invalid characters: "
|
||||
<< j_invalid.dump(-1, ' ', false, json::error_handler_t::ignore)
|
||||
<< '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/dump.output"
|
||||
objects:
|
||||
{"one":1,"two":2}
|
||||
|
||||
{"one":1,"two":2}
|
||||
|
||||
{
|
||||
"one": 1,
|
||||
"two": 2
|
||||
}
|
||||
|
||||
{
|
||||
"one": 1,
|
||||
"two": 2
|
||||
}
|
||||
|
||||
{
|
||||
"one": 1,
|
||||
"two": 2
|
||||
}
|
||||
|
||||
arrays:
|
||||
[1,2,4,8,16]
|
||||
|
||||
[1,2,4,8,16]
|
||||
|
||||
[
|
||||
1,
|
||||
2,
|
||||
4,
|
||||
8,
|
||||
16
|
||||
]
|
||||
|
||||
[
|
||||
1,
|
||||
2,
|
||||
4,
|
||||
8,
|
||||
16
|
||||
]
|
||||
|
||||
[
|
||||
1,
|
||||
2,
|
||||
4,
|
||||
8,
|
||||
16
|
||||
]
|
||||
|
||||
strings:
|
||||
"Hellö 😀!"
|
||||
"Hell\u00f6 \ud83d\ude00!"
|
||||
[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9
|
||||
string with replaced invalid characters: "ä�ü"
|
||||
string with ignored invalid characters: "äü"
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/dump/" rel="canonical"><link href=../diff/ rel=prev><link href=../emplace/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>dump - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsondump class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> dump </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div classLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/dump/" rel="canonical"><link href=../diff/ rel=prev><link href=../emplace/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>dump - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsondump class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> dump </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div classLine truncated
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=w> </span><span class=n>indent_char</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sc>' '</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ensure_ascii</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>error_handler_t</span><span class=w> </span><span class=n>error_handler</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>error_handler_t</span><span class=o>::</span><span class=n>strict</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
|
||||
@@ -52,13 +52,50 @@ Logarithmic in the size of the container, O(log(`size()`)).
|
||||
the same key.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/emplace.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json object = {{"one", 1}, {"two", 2}};
|
||||
json null;
|
||||
|
||||
// print values
|
||||
std::cout << object << '\n';
|
||||
std::cout << null << '\n';
|
||||
|
||||
// add values
|
||||
auto res1 = object.emplace("three", 3);
|
||||
null.emplace("A", "a");
|
||||
null.emplace("B", "b");
|
||||
|
||||
// the following call will not add an object, because there is already
|
||||
// a value stored at key "B"
|
||||
auto res2 = null.emplace("B", "c");
|
||||
|
||||
// print values
|
||||
std::cout << object << '\n';
|
||||
std::cout << *res1.first << " " << std::boolalpha << res1.second << '\n';
|
||||
|
||||
std::cout << null << '\n';
|
||||
std::cout << *res2.first << " " << std::boolalpha << res2.second << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/emplace.output"
|
||||
{"one":1,"two":2}
|
||||
null
|
||||
{"one":1,"three":3,"two":2}
|
||||
3 true
|
||||
{"A":"a","B":"b"}
|
||||
"b" false
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/emplace/" rel="canonical"><link href=../dump/ rel=prev><link href=../emplace_back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>emplace - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonemplace class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> emplace </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/emplace/" rel="canonical"><link href=../dump/ rel=prev><link href=../emplace_back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>emplace - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> emplace </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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|
||||
<span class=n>std</span><span class=o>::</span><span class=n>pair</span><span class=o><</span><span class=n>iterator</span><span class=p>,</span><span class=w> </span><span class=kt>bool</span><span class=o>></span><span class=w> </span><span class=n>emplace</span><span class=p>(</span><span class=n>Args</span><span class=o>&&</span><span class=w> </span><span class=p>...</span><span class=w> </span><span class=n>args</span><span class=p>);</span>
|
||||
</code></pre></div> <p>Inserts a new element into a <abbr title="JavaScript Object Notation">JSON</abbr> object constructed in-place with the given <code>args</code> if there is no element with the key in the container. If the function is called on a <abbr title="JavaScript Object Notation">JSON</abbr> null value, an empty object is created before appending the value created from <code>args</code>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>Args</code></dt> <dd>compatible types to create a <code>basic_json</code> object</dd> </dl> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">¶</a></h2> <p>For <a href=../../ordered_json/ ><code>ordered_json</code></a>, adding a value to an object can yield a reallocation, in which case all iterators (including the <code>end()</code> iterator) and all references to the elements are invalidated.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>args</code> (in)</dt> <dd>arguments to forward to a constructor of <code>basic_json</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a <code class=highlight><span class=kt>bool</span></code> denoting whether the insertion took place.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value. As an exception, a <code class=highlight><span class=kc>null</span></code> value is converted to an empty object before the element is added and keeps that type if adding the element throws.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error311><code>type_error.311</code></a> when called on a type other than <abbr title="JavaScript Object Notation">JSON</abbr> object or <code class=highlight><span class=kc>null</span></code>; example: <code>"cannot use emplace() with number"</code></p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Logarithmic in the size of the container, O(log(<code>size()</code>)).</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how <code>emplace()</code> can be used to add elements to a <abbr title="JavaScript Object Notation">JSON</abbr> object. Note how the <code class=highlight><span class=kc>null</span></code> value was silently converted to a <abbr title="JavaScript Object Notation">JSON</abbr> object. Further note how no value is added if there was already one value stored with the same key.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -50,13 +50,41 @@ Amortized constant.
|
||||
silently converted to a JSON array.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/emplace_back.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json array = {1, 2, 3, 4, 5};
|
||||
json null;
|
||||
|
||||
// print values
|
||||
std::cout << array << '\n';
|
||||
std::cout << null << '\n';
|
||||
|
||||
// add values
|
||||
array.emplace_back(6);
|
||||
null.emplace_back("first");
|
||||
null.emplace_back(3, "second");
|
||||
|
||||
// print values
|
||||
std::cout << array << '\n';
|
||||
std::cout << null << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/emplace_back.output"
|
||||
[1,2,3,4,5]
|
||||
null
|
||||
[1,2,3,4,5,6]
|
||||
["first",["second","second","second"]]
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/emplace_back/" rel="canonical"><link href=../emplace/ rel=prev><link href=../empty/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>emplace_back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> emplace_back </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/emplace_back/" rel="canonical"><link href=../emplace/ rel=prev><link href=../empty/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>emplace_back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> emplace_back </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9Line truncated
|
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<span class=n>reference</span><span class=w> </span><span class=n>emplace_back</span><span class=p>(</span><span class=n>Args</span><span class=o>&&</span><span class=w> </span><span class=p>...</span><span class=w> </span><span class=n>args</span><span class=p>);</span>
|
||||
</code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> value from the passed parameters <code>args</code> to the end of the <abbr title="JavaScript Object Notation">JSON</abbr> value. If the function is called on a <abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=kc>null</span></code> value, an empty array is created before appending the value created from <code>args</code>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>Args</code></dt> <dd>compatible types to create a <code>basic_json</code> object</dd> </dl> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">¶</a></h2> <p>By adding an element to the end of the array, a reallocation can happen, in which case all iterators (including the <a href=../end/ ><code>end()</code></a> iterator) and all references to the elements are invalidated. Otherwise, only the <a href=../end/ ><code>end()</code></a> iterator is invalidated.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>args</code> (in)</dt> <dd>arguments to forward to a constructor of <code>basic_json</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>reference to the inserted element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value. As an exception, a <code class=highlight><span class=kc>null</span></code> value is converted to an empty array before the element is added and keeps that type if adding the element throws.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error311><code>type_error.311</code></a> when called on a type other than <abbr title="JavaScript Object Notation">JSON</abbr> array or <code class=highlight><span class=kc>null</span></code>; example: <code>"cannot use emplace_back() with number"</code></p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Amortized constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how <code>emplace_back()</code> can be used to add elements to a <abbr title="JavaScript Object Notation">JSON</abbr> array. Note how the <code>null</code> value was silently converted to a <abbr title="JavaScript Object Notation">JSON</abbr> array.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
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<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
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|
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+41
-2
@@ -51,13 +51,52 @@ itself is empty which is `#!cpp false` in the case of a string.
|
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The following code uses `empty()` to check if a JSON object contains any elements.
|
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|
||||
```cpp
|
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--8<-- "examples/empty.cpp"
|
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#include <iostream>
|
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#include <nlohmann/json.hpp>
|
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|
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using json = nlohmann::json;
|
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|
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int main()
|
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{
|
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// create JSON values
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json j_null;
|
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json j_boolean = true;
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json j_number_integer = 17;
|
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json j_number_float = 23.42;
|
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json j_object = {{"one", 1}, {"two", 2}};
|
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json j_object_empty(json::value_t::object);
|
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json j_array = {1, 2, 4, 8, 16};
|
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json j_array_empty(json::value_t::array);
|
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json j_string = "Hello, world";
|
||||
|
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// call empty()
|
||||
std::cout << std::boolalpha;
|
||||
std::cout << j_null.empty() << '\n';
|
||||
std::cout << j_boolean.empty() << '\n';
|
||||
std::cout << j_number_integer.empty() << '\n';
|
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std::cout << j_number_float.empty() << '\n';
|
||||
std::cout << j_object.empty() << '\n';
|
||||
std::cout << j_object_empty.empty() << '\n';
|
||||
std::cout << j_array.empty() << '\n';
|
||||
std::cout << j_array_empty.empty() << '\n';
|
||||
std::cout << j_string.empty() << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/empty.output"
|
||||
true
|
||||
false
|
||||
false
|
||||
false
|
||||
false
|
||||
true
|
||||
false
|
||||
true
|
||||
false
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/empty/" rel="canonical"><link href=../emplace_back/ rel=prev><link href=../end/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>empty - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> empty </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/empty/" rel="canonical"><link href=../emplace_back/ rel=prev><link href=../end/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>empty - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> empty </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
||||
</code></pre></div> <p>Checks if a <abbr title="JavaScript Object Notation">JSON</abbr> value has no elements (i.e., whether its <a href=../size/ ><code>size()</code></a> is <code>0</code>).</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>The return value depends on the different types and is defined as follows:</p> <table> <thead> <tr> <th>Value type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td>boolean</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>string</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>number</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>binary</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>object</td> <td>result of function <code>object_t::empty()</code></td> </tr> <tr> <td>array</td> <td>result of function <code>array_t::empty()</code></td> </tr> </tbody> </table> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant, as long as <a href=../array_t/ ><code>array_t</code></a> and <a href=../object_t/ ><code>object_t</code></a> satisfy the <a href="https://en.cppreference.com/w/cpp/named_req/Container">Container</a> concept; that is, their <code>empty()</code> functions have constant complexity.</p> <h2 id=possible-implementation>Possible implementation<a class=headerlink href=#possible-implementation title="Permanent link">¶</a></h2> <div class=highlight><pre><span></span><code><span class=kt>bool</span><span class=w> </span><span class=nf>empty</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span>
|
||||
<span class=p>{</span>
|
||||
<span class=w> </span><span class=k>return</span><span class=w> </span><span class=n>size</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=mi>0</span><span class=p>;</span>
|
||||
|
||||
+22
-2
@@ -28,13 +28,33 @@ Constant.
|
||||
The following code shows an example for `end()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/end.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create an array value
|
||||
json array = {1, 2, 3, 4, 5};
|
||||
|
||||
// get an iterator to one past the last element
|
||||
json::iterator it = array.end();
|
||||
|
||||
// decrement the iterator to point to the last element
|
||||
--it;
|
||||
|
||||
// serialize the element that the iterator points to
|
||||
std::cout << *it << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/end.output"
|
||||
5
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/end/" rel="canonical"><link href=../empty/ rel=prev><link href=../end_pos/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>end - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonend class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> end </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=mdLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/end/" rel="canonical"><link href=../empty/ rel=prev><link href=../end_pos/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>end - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonend class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> end </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=mdLine truncated
|
||||
<span class=n>const_iterator</span><span class=w> </span><span class=nf>end</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
|
||||
</code></pre></div> <p>Returns an iterator to one past the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>end()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
+103
-2
@@ -47,13 +47,114 @@ Constant.
|
||||
??? example "Example"
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/diagnostic_positions.cpp"
|
||||
#include <iostream>
|
||||
|
||||
#define JSON_DIAGNOSTIC_POSITIONS 1
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
std::string json_string = R"(
|
||||
{
|
||||
"address": {
|
||||
"street": "Fake Street",
|
||||
"housenumber": 1
|
||||
}
|
||||
}
|
||||
)";
|
||||
json j = json::parse(json_string);
|
||||
|
||||
std::cout << "Root diagnostic positions: \n";
|
||||
std::cout << "\tstart_pos: " << j.start_pos() << '\n';
|
||||
std::cout << "\tend_pos:" << j.end_pos() << "\n";
|
||||
std::cout << "Original string: \n";
|
||||
std::cout << "{\n \"address\": {\n \"street\": \"Fake Street\",\n \"housenumber\": 1\n }\n }" << "\n";
|
||||
std::cout << "Parsed string: \n";
|
||||
std::cout << json_string.substr(j.start_pos(), j.end_pos() - j.start_pos()) << "\n\n";
|
||||
|
||||
std::cout << "address diagnostic positions: \n";
|
||||
std::cout << "\tstart_pos:" << j["address"].start_pos() << '\n';
|
||||
std::cout << "\tend_pos:" << j["address"].end_pos() << "\n\n";
|
||||
std::cout << "Original string: \n";
|
||||
std::cout << "{ \"street\": \"Fake Street\",\n \"housenumber\": 1\n }" << "\n";
|
||||
std::cout << "Parsed string: \n";
|
||||
std::cout << json_string.substr(j["address"].start_pos(), j["address"].end_pos() - j["address"].start_pos()) << "\n\n";
|
||||
|
||||
std::cout << "street diagnostic positions: \n";
|
||||
std::cout << "\tstart_pos:" << j["address"]["street"].start_pos() << '\n';
|
||||
std::cout << "\tend_pos:" << j["address"]["street"].end_pos() << "\n\n";
|
||||
std::cout << "Original string: \n";
|
||||
std::cout << "\"Fake Street\"" << "\n";
|
||||
std::cout << "Parsed string: \n";
|
||||
std::cout << json_string.substr(j["address"]["street"].start_pos(), j["address"]["street"].end_pos() - j["address"]["street"].start_pos()) << "\n\n";
|
||||
|
||||
std::cout << "housenumber diagnostic positions: \n";
|
||||
std::cout << "\tstart_pos:" << j["address"]["housenumber"].start_pos() << '\n';
|
||||
std::cout << "\tend_pos:" << j["address"]["housenumber"].end_pos() << "\n\n";
|
||||
std::cout << "Original string: \n";
|
||||
std::cout << "1" << "\n";
|
||||
std::cout << "Parsed string: \n";
|
||||
std::cout << json_string.substr(j["address"]["housenumber"].start_pos(), j["address"]["housenumber"].end_pos() - j["address"]["housenumber"].start_pos()) << "\n\n";
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```
|
||||
--8<-- "examples/diagnostic_positions.output"
|
||||
Root diagnostic positions:
|
||||
start_pos: 5
|
||||
end_pos:109
|
||||
Original string:
|
||||
{
|
||||
"address": {
|
||||
"street": "Fake Street",
|
||||
"housenumber": 1
|
||||
}
|
||||
}
|
||||
Parsed string:
|
||||
{
|
||||
"address": {
|
||||
"street": "Fake Street",
|
||||
"housenumber": 1
|
||||
}
|
||||
}
|
||||
|
||||
address diagnostic positions:
|
||||
start_pos:26
|
||||
end_pos:103
|
||||
|
||||
Original string:
|
||||
{ "street": "Fake Street",
|
||||
"housenumber": 1
|
||||
}
|
||||
Parsed string:
|
||||
{
|
||||
"street": "Fake Street",
|
||||
"housenumber": 1
|
||||
}
|
||||
|
||||
street diagnostic positions:
|
||||
start_pos:50
|
||||
end_pos:63
|
||||
|
||||
Original string:
|
||||
"Fake Street"
|
||||
Parsed string:
|
||||
"Fake Street"
|
||||
|
||||
housenumber diagnostic positions:
|
||||
start_pos:92
|
||||
end_pos:93
|
||||
|
||||
Original string:
|
||||
1
|
||||
Parsed string:
|
||||
1
|
||||
|
||||
|
||||
```
|
||||
|
||||
The output shows the start/end positions of all the objects and fields in the JSON string.
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/end_pos/" rel="canonical"><link href=../end/ rel=prev><link href=../erase/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>end_pos - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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|
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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/end_pos/" rel="canonical"><link href=../end/ rel=prev><link href=../erase/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>end_pos - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> end_pos </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <Line truncated
|
||||
<span class=k>constexpr</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=w> </span><span class=nf>end_pos</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
|
||||
<span class=cp>#endif</span>
|
||||
</code></pre></div> <p>Returns the position immediately following the last character of the <abbr title="JavaScript Object Notation">JSON</abbr> string from which the value was parsed from.</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td>object</td> <td>position after the closing <code>}</code></td> </tr> <tr> <td>array</td> <td>position after the closing <code>]</code></td> </tr> <tr> <td>string</td> <td>position after the closing <code>"</code></td> </tr> <tr> <td>number</td> <td>position after the last character</td> </tr> <tr> <td>boolean</td> <td>position after <code>e</code></td> </tr> <tr> <td>null</td> <td>position after <code>l</code></td> </tr> </tbody> </table> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>the position of the character <em>following</em> the last character of the given value in the parsed <abbr title="JavaScript Object Notation">JSON</abbr> string, if the value was created by the <a href=../parse/ ><code>parse</code></a> function, or <code>std::string::npos</code> if the value was constructed otherwise</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition note"> <p class=admonition-title>Note</p> <p>The function is only available if macro <a href=../../macros/json_diagnostic_positions/ ><code>JSON_DIAGNOSTIC_POSITIONS</code></a> has been defined to <code class=highlight><span class=mi>1</span></code> before including the library header.</p> </div> <div class="admonition warning"> <p class=admonition-title>Invalidation</p> <p>The returned positions are only valid as long as the <abbr title="JavaScript Object Notation">JSON</abbr> value is not changed. The positions are <em>not</em> updated when the <abbr title="JavaScript Object Notation">JSON</abbr> value is changed.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
|
||||
+143
-10
@@ -137,13 +137,50 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
The example shows the effect of `erase()` for different JSON types using an iterator.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/erase__IteratorType.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json j_boolean = true;
|
||||
json j_number_integer = 17;
|
||||
json j_number_float = 23.42;
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
json j_array = {1, 2, 4, 8, 16};
|
||||
json j_string = "Hello, world";
|
||||
|
||||
// call erase()
|
||||
j_boolean.erase(j_boolean.begin());
|
||||
j_number_integer.erase(j_number_integer.begin());
|
||||
j_number_float.erase(j_number_float.begin());
|
||||
j_object.erase(j_object.find("two"));
|
||||
j_array.erase(j_array.begin() + 2);
|
||||
j_string.erase(j_string.begin());
|
||||
|
||||
// print values
|
||||
std::cout << j_boolean << '\n';
|
||||
std::cout << j_number_integer << '\n';
|
||||
std::cout << j_number_float << '\n';
|
||||
std::cout << j_object << '\n';
|
||||
std::cout << j_array << '\n';
|
||||
std::cout << j_string << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/erase__IteratorType.output"
|
||||
null
|
||||
null
|
||||
null
|
||||
{"one":1}
|
||||
[1,2,8,16]
|
||||
null
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) remove elements given an iterator range"
|
||||
@@ -151,13 +188,50 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
The example shows the effect of `erase()` for different JSON types using an iterator range.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/erase__IteratorType_IteratorType.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json j_boolean = true;
|
||||
json j_number_integer = 17;
|
||||
json j_number_float = 23.42;
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
json j_array = {1, 2, 4, 8, 16};
|
||||
json j_string = "Hello, world";
|
||||
|
||||
// call erase()
|
||||
j_boolean.erase(j_boolean.begin(), j_boolean.end());
|
||||
j_number_integer.erase(j_number_integer.begin(), j_number_integer.end());
|
||||
j_number_float.erase(j_number_float.begin(), j_number_float.end());
|
||||
j_object.erase(j_object.find("two"), j_object.end());
|
||||
j_array.erase(j_array.begin() + 1, j_array.begin() + 3);
|
||||
j_string.erase(j_string.begin(), j_string.end());
|
||||
|
||||
// print values
|
||||
std::cout << j_boolean << '\n';
|
||||
std::cout << j_number_integer << '\n';
|
||||
std::cout << j_number_float << '\n';
|
||||
std::cout << j_object << '\n';
|
||||
std::cout << j_array << '\n';
|
||||
std::cout << j_string << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/erase__IteratorType_IteratorType.output"
|
||||
null
|
||||
null
|
||||
null
|
||||
{"one":1}
|
||||
[1,8,16]
|
||||
null
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (3) remove element from a JSON object given a key"
|
||||
@@ -165,13 +239,33 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
The example shows the effect of `erase()` for different JSON types using an object key.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/erase__object_t_key_type.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON object
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
|
||||
// call erase()
|
||||
auto count_one = j_object.erase("one");
|
||||
auto count_three = j_object.erase("three");
|
||||
|
||||
// print values
|
||||
std::cout << j_object << '\n';
|
||||
std::cout << count_one << " " << count_three << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/erase__object_t_key_type.output"
|
||||
{"two":2}
|
||||
1 0
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (4) remove element from a JSON object given a key using string_view"
|
||||
@@ -179,13 +273,35 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
The example shows the effect of `erase()` for different JSON types using an object key.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/erase__keytype.c++17.cpp"
|
||||
#include <iostream>
|
||||
#include <string_view>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using namespace std::string_view_literals;
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON object
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
|
||||
// call erase()
|
||||
auto count_one = j_object.erase("one"sv);
|
||||
auto count_three = j_object.erase("three"sv);
|
||||
|
||||
// print values
|
||||
std::cout << j_object << '\n';
|
||||
std::cout << count_one << " " << count_three << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/erase__keytype.c++17.output"
|
||||
{"two":2}
|
||||
1 0
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (5) remove element from a JSON array given an index"
|
||||
@@ -193,13 +309,30 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
The example shows the effect of `erase()` using an array index.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/erase__size_type.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON array
|
||||
json j_array = {0, 1, 2, 3, 4, 5};
|
||||
|
||||
// call erase()
|
||||
j_array.erase(2);
|
||||
|
||||
// print values
|
||||
std::cout << j_array << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/erase__size_type.output"
|
||||
[0,1,3,4,5]
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/erase/" rel="canonical"><link href=../end_pos/ rel=prev><link href=../error_handler_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>erase - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonerase class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> erase </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </laLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/erase/" rel="canonical"><link href=../end_pos/ rel=prev><link href=../error_handler_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>erase - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonerase class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> erase </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </laLine truncated
|
||||
<span class=n>iterator</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>iterator</span><span class=w> </span><span class=n>pos</span><span class=p>);</span>
|
||||
<span class=n>const_iterator</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>const_iterator</span><span class=w> </span><span class=n>pos</span><span class=p>);</span>
|
||||
|
||||
|
||||
@@ -37,8 +37,8 @@ ignore
|
||||
: ignore invalid UTF-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped
|
||||
|
||||
keep
|
||||
: keep invalid UTF-8 sequences unchanged; only meaningful for the binary formats mentioned above, since [`dump`]
|
||||
(dump.md) itself must produce text, and `keep` there writes the ill-formed bytes to the output as is, so the
|
||||
: keep invalid UTF-8 sequences unchanged; only meaningful for the binary formats mentioned above, since
|
||||
[`dump`](dump.md) itself must produce text, and `keep` there writes the ill-formed bytes to the output as is, so the
|
||||
result is then not valid UTF-8 (but still equals the input bytes exactly, including around any well-formed
|
||||
characters, which are still escaped as usual)
|
||||
|
||||
@@ -50,13 +50,42 @@ keep
|
||||
[`dump`](dump.md) when reading serializing an invalid UTF-8 sequence.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/error_handler_t.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON value with invalid UTF-8 byte sequence
|
||||
json j_invalid = "ä\xA9ü";
|
||||
try
|
||||
{
|
||||
std::cout << j_invalid.dump() << std::endl;
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << std::endl;
|
||||
}
|
||||
|
||||
std::cout << "string with replaced invalid characters: "
|
||||
<< j_invalid.dump(-1, ' ', false, json::error_handler_t::replace)
|
||||
<< "\nstring with ignored invalid characters: "
|
||||
<< j_invalid.dump(-1, ' ', false, json::error_handler_t::ignore)
|
||||
<< "\nstring with the invalid byte kept as is (" << j_invalid.dump(-1, ' ', false, json::error_handler_t::keep).size()
|
||||
<< " bytes, not valid UTF-8 itself)\n";
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/error_handler_t.output"
|
||||
[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9
|
||||
string with replaced invalid characters: "ä�ü"
|
||||
string with ignored invalid characters: "äü"
|
||||
string with the invalid byte kept as is (7 bytes, not valid UTF-8 itself)
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,10 +1,10 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/error_handler_t/" rel="canonical"><link href=../erase/ rel=prev><link href=../exception/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>error_handler_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonerror_handler_t class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> error_handler_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/error_handler_t/" rel="canonical"><link href=../erase/ rel=prev><link href=../exception/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>error_handler_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> error_handler_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12Line truncated
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<span class=w> </span><span class=n>strict</span><span class=p>,</span>
|
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<span class=w> </span><span class=n>replace</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=n>ignore</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=n>keep</span>
|
||||
<span class=p>};</span>
|
||||
</code></pre></div> <p>This enumeration is used to choose how to treat ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in a string value or object key:</p> <ul> <li><a href=../dump/ ><code>dump</code></a> uses it while serializing a <code>basic_json</code> value to text.</li> <li><a href=../to_cbor/ ><code>to_cbor</code></a>, <a href=../to_msgpack/ ><code>to_msgpack</code></a>, <a href=../to_ubjson/ ><code>to_ubjson</code></a>, <a href=../to_bjdata/ ><code>to_bjdata</code></a>, and <a href=../to_bson/ ><code>to_bson</code></a> use it while serializing a <code>basic_json</code> value to that binary format. Their default is <code>keep</code>, as no binary writer checked before this parameter was added. <abbr title="Concise Binary Object Representation">CBOR</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>, <abbr title="Binary JData">BJData</abbr>, and <abbr title="Binary JSON">BSON</abbr> require valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, so for these four the default is <code>strict</code> if <a href=../../macros/json_strict_binary_utf8/ ><code>JSON_STRICT_BINARY_UTF8</code></a> is enabled; MessagePack's specification explicitly allows a string to contain ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8, so <code>to_msgpack</code> stays at <code>keep</code>. <code>to_bon8</code> does not take this parameter: <abbr title="Binary Object Notation 8">BON8</abbr> always validates, since <abbr title="Unicode Transformation Format">UTF</abbr>-8 lead bytes are structural to that format.</li> <li><a href=../from_cbor/ ><code>from_cbor</code></a>, <a href=../from_msgpack/ ><code>from_msgpack</code></a>, <a href=../from_ubjson/ ><code>from_ubjson</code></a>, <a href=../from_bjdata/ ><code>from_bjdata</code></a>, and <a href=../from_bson/ ><code>from_bson</code></a> use it while parsing that binary format, to decide whether to check a string value or object key for well-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 at all; by default (<code>keep</code>) they do not, as no binary reader did before this parameter was added. <code>from_bon8</code> does not take this parameter, for the same reason <code>to_bon8</code> does not.</li> </ul> <p>Four values are differentiated:</p> <dl> <dt>strict</dt> <dd>throw a <code>type_error</code>/<code>parse_error</code> exception in case of invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</dd> <dt>replace</dt> <dd>replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD (� REPLACEMENT CHARACTER)</dd> <dt>ignore</dt> <dd>ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped</dd> <dt>keep</dt> <dd>keep invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences unchanged; only meaningful for the binary formats mentioned above, since [<code>dump</code>] (dump.md) itself must produce text, and <code>keep</code> there writes the ill-formed bytes to the output as is, so the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 (but still equals the input bytes exactly, including around any well-formed characters, which are still escaped as usual)</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how the different values of the <code>error_handler_t</code> influence the behavior of <a href=../dump/ ><code>dump</code></a> when reading serializing an invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequence.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
</code></pre></div> <p>This enumeration is used to choose how to treat ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in a string value or object key:</p> <ul> <li><a href=../dump/ ><code>dump</code></a> uses it while serializing a <code>basic_json</code> value to text.</li> <li><a href=../to_cbor/ ><code>to_cbor</code></a>, <a href=../to_msgpack/ ><code>to_msgpack</code></a>, <a href=../to_ubjson/ ><code>to_ubjson</code></a>, <a href=../to_bjdata/ ><code>to_bjdata</code></a>, and <a href=../to_bson/ ><code>to_bson</code></a> use it while serializing a <code>basic_json</code> value to that binary format. Their default is <code>keep</code>, as no binary writer checked before this parameter was added. <abbr title="Concise Binary Object Representation">CBOR</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>, <abbr title="Binary JData">BJData</abbr>, and <abbr title="Binary JSON">BSON</abbr> require valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, so for these four the default is <code>strict</code> if <a href=../../macros/json_strict_binary_utf8/ ><code>JSON_STRICT_BINARY_UTF8</code></a> is enabled; MessagePack's specification explicitly allows a string to contain ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8, so <code>to_msgpack</code> stays at <code>keep</code>. <code>to_bon8</code> does not take this parameter: <abbr title="Binary Object Notation 8">BON8</abbr> always validates, since <abbr title="Unicode Transformation Format">UTF</abbr>-8 lead bytes are structural to that format.</li> <li><a href=../from_cbor/ ><code>from_cbor</code></a>, <a href=../from_msgpack/ ><code>from_msgpack</code></a>, <a href=../from_ubjson/ ><code>from_ubjson</code></a>, <a href=../from_bjdata/ ><code>from_bjdata</code></a>, and <a href=../from_bson/ ><code>from_bson</code></a> use it while parsing that binary format, to decide whether to check a string value or object key for well-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 at all; by default (<code>keep</code>) they do not, as no binary reader did before this parameter was added. <code>from_bon8</code> does not take this parameter, for the same reason <code>to_bon8</code> does not.</li> </ul> <p>Four values are differentiated:</p> <dl> <dt>strict</dt> <dd>throw a <code>type_error</code>/<code>parse_error</code> exception in case of invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</dd> <dt>replace</dt> <dd>replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD (� REPLACEMENT CHARACTER)</dd> <dt>ignore</dt> <dd>ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped</dd> <dt>keep</dt> <dd>keep invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences unchanged; only meaningful for the binary formats mentioned above, since <a href=../dump/ ><code>dump</code></a> itself must produce text, and <code>keep</code> there writes the ill-formed bytes to the output as is, so the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 (but still equals the input bytes exactly, including around any well-formed characters, which are still escaped as usual)</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how the different values of the <code>error_handler_t</code> influence the behavior of <a href=../dump/ ><code>dump</code></a> when reading serializing an invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequence.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
@@ -33,4 +33,4 @@
|
||||
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>replaced</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"ä�ü"</span>
|
||||
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>ig</span><span class=kc>n</span><span class=err>ored</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"äü"</span>
|
||||
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=kc>t</span><span class=err>he</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=w> </span><span class=err>kep</span><span class=kc>t</span><span class=w> </span><span class=err>as</span><span class=w> </span><span class=err>is</span><span class=w> </span><span class=err>(</span><span class=mi>7</span><span class=w> </span><span class=err>by</span><span class=kc>tes</span><span class=p>,</span><span class=w> </span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=w> </span><span class=err>valid</span><span class=w> </span><span class=err>UTF</span><span class=mi>-8</span><span class=w> </span><span class=err>i</span><span class=kc>tself</span><span class=err>)</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../dump/ >dump</a> serializes a <abbr title="JavaScript Object Notation">JSON</abbr> value, with an <code>error_handler_t</code> parameter to configure invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 handling</li> <li><a href=../../../features/serialization/#handling-invalid-utf-8>Handling invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</a> - the article on handling invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.4.0.</li> <li>Added <code>keep</code>, and made this enumeration apply to the binary readers and writers in addition to <code>dump</code>, in version 3.13.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 10:13:49 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0Line truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../dump/ >dump</a> serializes a <abbr title="JavaScript Object Notation">JSON</abbr> value, with an <code>error_handler_t</code> parameter to configure invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 handling</li> <li><a href=../../../features/serialization/#handling-invalid-utf-8>Handling invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</a> - the article on handling invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.4.0.</li> <li>Added <code>keep</code>, and made this enumeration apply to the binary readers and writers in addition to <code>dump</code>, in version 3.13.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5Line truncated
|
||||
@@ -23,7 +23,7 @@ replace : replace invalid UTF-8 sequences with U+FFFD (� REPLACEMENT CHARACTER
|
||||
|
||||
ignore : ignore invalid UTF-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped
|
||||
|
||||
keep : keep invalid UTF-8 sequences unchanged; only meaningful for the binary formats mentioned above, since \[`dump`\] (dump.md) itself must produce text, and `keep` there writes the ill-formed bytes to the output as is, so the result is then not valid UTF-8 (but still equals the input bytes exactly, including around any well-formed characters, which are still escaped as usual)
|
||||
keep : keep invalid UTF-8 sequences unchanged; only meaningful for the binary formats mentioned above, since [`dump`](https://json.nlohmann.me/api/basic_json/dump/index.md) itself must produce text, and `keep` there writes the ill-formed bytes to the output as is, so the result is then not valid UTF-8 (but still equals the input bytes exactly, including around any well-formed characters, which are still escaped as usual)
|
||||
|
||||
## Examples
|
||||
|
||||
|
||||
@@ -69,13 +69,35 @@ constructor.
|
||||
The following code shows how arbitrary library exceptions can be caught.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/exception.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
try
|
||||
{
|
||||
// calling at() for a non-existing key
|
||||
json j = {{"foo", "bar"}};
|
||||
json k = j.at("non-existing");
|
||||
}
|
||||
catch (const json::exception& e)
|
||||
{
|
||||
// output exception information
|
||||
std::cout << "message: " << e.what() << '\n'
|
||||
<< "exception id: " << e.id << std::endl;
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/exception.output"
|
||||
message: [json.exception.out_of_range.403] key 'non-existing' not found
|
||||
exception id: 403
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/exception/" rel="canonical"><link href=../error_handler_t/ rel=prev><link href=../find/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>exception - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonexception class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> exception </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/exception/" rel="canonical"><link href=../error_handler_t/ rel=prev><link href=../find/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>exception - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonexception class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> exception </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"Line truncated
|
||||
</code></pre></div> <p>This class is an extension of <a href="https://en.cppreference.com/w/cpp/error/exception"><code>std::exception</code></a> objects with a member <code>id</code> for exception ids. It is used as the base class for all exceptions thrown by the <code>basic_json</code> class. This class can hence be used as "wildcard" to catch exceptions, see example below.</p> <pre class=mermaid><code>classDiagram
|
||||
direction LR
|
||||
|
||||
|
||||
+61
-4
@@ -10,12 +10,21 @@ template<typename KeyType>
|
||||
iterator find(KeyType&& key);
|
||||
template<typename KeyType>
|
||||
const_iterator find(KeyType&& key) const;
|
||||
|
||||
// (3)
|
||||
template<typename T>
|
||||
iterator find(T) = delete;
|
||||
template<typename T>
|
||||
const_iterator find(T) const = delete;
|
||||
```
|
||||
|
||||
1. Finds an element in a JSON object with a key equivalent to `key`. If the element is not found or the
|
||||
JSON value is not an object, `end()` is returned.
|
||||
2. See 1. This overload is only available if `KeyType` is comparable with `#!cpp typename object_t::key_type` and
|
||||
`#!cpp typename object_comparator_t::is_transparent` denotes a type.
|
||||
3. Deleted: this overload is only available if `T` is an integral type and is declared as deleted, so that a call with
|
||||
an integer `key` (for example, `#!cpp j.find(0)`) fails to compile. Otherwise, the integer literal `0` would convert to
|
||||
a null `#!cpp const char*` and, from there, to the key type, causing undefined behavior at runtime.
|
||||
|
||||
## Template parameters
|
||||
|
||||
@@ -57,13 +66,36 @@ Logarithmic in the size of the JSON object.
|
||||
The example shows how `find()` is used.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/find__object_t_key_type.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON object
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
|
||||
// call find
|
||||
auto it_two = j_object.find("two");
|
||||
auto it_three = j_object.find("three");
|
||||
|
||||
// print values
|
||||
std::cout << std::boolalpha;
|
||||
std::cout << "\"two\" was found: " << (it_two != j_object.end()) << '\n';
|
||||
std::cout << "value at key \"two\": " << *it_two << '\n';
|
||||
std::cout << "\"three\" was found: " << (it_three != j_object.end()) << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/find__object_t_key_type.output"
|
||||
"two" was found: true
|
||||
value at key "two": 2
|
||||
"three" was found: false
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) find object element by key using string_view"
|
||||
@@ -71,13 +103,38 @@ Logarithmic in the size of the JSON object.
|
||||
The example shows how `find()` is used.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/find__keytype.c++17.cpp"
|
||||
#include <iostream>
|
||||
#include <string_view>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using namespace std::string_view_literals;
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON object
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
|
||||
// call find
|
||||
auto it_two = j_object.find("two"sv);
|
||||
auto it_three = j_object.find("three"sv);
|
||||
|
||||
// print values
|
||||
std::cout << std::boolalpha;
|
||||
std::cout << "\"two\" was found: " << (it_two != j_object.end()) << '\n';
|
||||
std::cout << "value at key \"two\": " << *it_two << '\n';
|
||||
std::cout << "\"three\" was found: " << (it_three != j_object.end()) << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/find__keytype.c++17.output"
|
||||
"two" was found: true
|
||||
value at key "two": 2
|
||||
"three" was found: false
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/find/" rel="canonical"><link href=../exception/ rel=prev><link href=../flatten/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>find - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfind class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> find </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/find/" rel="canonical"><link href=../exception/ rel=prev><link href=../flatten/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>find - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfind class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> find </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div Line truncated
|
||||
<span class=n>iterator</span><span class=w> </span><span class=nf>find</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&</span><span class=w> </span><span class=n>key</span><span class=p>);</span>
|
||||
<span class=n>const_iterator</span><span class=w> </span><span class=nf>find</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
|
||||
@@ -7,7 +7,13 @@
|
||||
<span class=n>iterator</span><span class=w> </span><span class=n>find</span><span class=p>(</span><span class=n>KeyType</span><span class=o>&&</span><span class=w> </span><span class=n>key</span><span class=p>);</span>
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>KeyType</span><span class=o>></span>
|
||||
<span class=n>const_iterator</span><span class=w> </span><span class=n>find</span><span class=p>(</span><span class=n>KeyType</span><span class=o>&&</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
</code></pre></div> <ol> <li>Finds an element in a <abbr title="JavaScript Object Notation">JSON</abbr> object with a key equivalent to <code>key</code>. If the element is not found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code>end()</code> is returned.</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value of the element to search for.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>Iterator to an element with a key equivalent to <code>key</code>. If no such element is found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, a past-the-end iterator (see <code>end()</code>) is returned.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <ul> <li>This method always returns <code>end()</code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>find</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To access an array element instead, use <a href=../at/ ><code>at</code></a>, <a href=../operator%5B%5D/ ><code>operator[]</code></a>, or compare against <a href=../size/ ><code>size</code></a>.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: (1) find object element by key</summary> <p>The example shows how <code>find()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
|
||||
<span class=c1>// (3)</span>
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=o>></span>
|
||||
<span class=n>iterator</span><span class=w> </span><span class=n>find</span><span class=p>(</span><span class=n>T</span><span class=p>)</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>delete</span><span class=p>;</span>
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=o>></span>
|
||||
<span class=n>const_iterator</span><span class=w> </span><span class=n>find</span><span class=p>(</span><span class=n>T</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>delete</span><span class=p>;</span>
|
||||
</code></pre></div> <ol> <li>Finds an element in a <abbr title="JavaScript Object Notation">JSON</abbr> object with a key equivalent to <code>key</code>. If the element is not found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code>end()</code> is returned.</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Deleted: this overload is only available if <code>T</code> is an integral type and is declared as deleted, so that a call with an integer <code>key</code> (for example, <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>find</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) fails to compile. Otherwise, the integer literal <code>0</code> would convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, to the key type, causing undefined behavior at runtime.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value of the element to search for.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>Iterator to an element with a key equivalent to <code>key</code>. If no such element is found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, a past-the-end iterator (see <code>end()</code>) is returned.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <ul> <li>This method always returns <code>end()</code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>find</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To access an array element instead, use <a href=../at/ ><code>at</code></a>, <a href=../operator%5B%5D/ ><code>operator[]</code></a>, or compare against <a href=../size/ ><code>size</code></a>.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: (1) find object element by key</summary> <p>The example shows how <code>find()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
@@ -55,4 +61,4 @@
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=s2>"two"</span><span class=w> </span><span class=err>was</span><span class=w> </span><span class=kc>f</span><span class=err>ou</span><span class=kc>n</span><span class=err>d</span><span class=p>:</span><span class=w> </span><span class=kc>true</span>
|
||||
<span class=err>value</span><span class=w> </span><span class=err>a</span><span class=kc>t</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=nt>"two"</span><span class=p>:</span><span class=w> </span><span class=mi>2</span>
|
||||
<span class=s2>"three"</span><span class=w> </span><span class=err>was</span><span class=w> </span><span class=kc>f</span><span class=err>ou</span><span class=kc>n</span><span class=err>d</span><span class=p>:</span><span class=w> </span><span class=kc>false</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../count/ >count</a> returns the number of occurrences of a key</li> <li><a href=../contains/ >contains</a> checks whether a key exists</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 1.0.0. Changed to support comparable types in version 3.11.0. Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to consistently accept <code>std::string_view</code>-convertible keys, as already supported by <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../value/ ><code>value</code></a>, and other lookup functions.</li> <li>Deleted overloads for integral key types added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 09:46:32 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/fLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../count/ >count</a> returns the number of occurrences of a key</li> <li><a href=../contains/ >contains</a> checks whether a key exists</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 1.0.0. Changed to support comparable types in version 3.11.0. Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to consistently accept <code>std::string_view</code>-convertible keys, as already supported by <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../value/ ><code>value</code></a>, and other lookup functions.</li> <li>Deleted overloads for integral key types added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/licenseLine truncated
|
||||
@@ -10,10 +10,17 @@ template<typename KeyType>
|
||||
iterator find(KeyType&& key);
|
||||
template<typename KeyType>
|
||||
const_iterator find(KeyType&& key) const;
|
||||
|
||||
// (3)
|
||||
template<typename T>
|
||||
iterator find(T) = delete;
|
||||
template<typename T>
|
||||
const_iterator find(T) const = delete;
|
||||
```
|
||||
|
||||
1. Finds an element in a JSON object with a key equivalent to `key`. If the element is not found or the JSON value is not an object, `end()` is returned.
|
||||
1. See 1. This overload is only available if `KeyType` is comparable with `typename object_t::key_type` and `typename object_comparator_t::is_transparent` denotes a type.
|
||||
1. Deleted: this overload is only available if `T` is an integral type and is declared as deleted, so that a call with an integer `key` (for example, `j.find(0)`) fails to compile. Otherwise, the integer literal `0` would convert to a null `const char*` and, from there, to the key type, causing undefined behavior at runtime.
|
||||
|
||||
## Template parameters
|
||||
|
||||
|
||||
@@ -32,13 +32,57 @@ Empty objects and arrays are flattened to `#!json null` and will not be reconstr
|
||||
The following code shows how a JSON object is flattened to an object whose keys consist of JSON pointers.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/flatten.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON value
|
||||
json j =
|
||||
{
|
||||
{"pi", 3.141},
|
||||
{"happy", true},
|
||||
{"name", "Niels"},
|
||||
{"nothing", nullptr},
|
||||
{
|
||||
"answer", {
|
||||
{"everything", 42}
|
||||
}
|
||||
},
|
||||
{"list", {1, 0, 2}},
|
||||
{
|
||||
"object", {
|
||||
{"currency", "USD"},
|
||||
{"value", 42.99}
|
||||
}
|
||||
}
|
||||
};
|
||||
|
||||
// call flatten()
|
||||
std::cout << std::setw(4) << j.flatten() << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/flatten.output"
|
||||
{
|
||||
"/answer/everything": 42,
|
||||
"/happy": true,
|
||||
"/list/0": 1,
|
||||
"/list/1": 0,
|
||||
"/list/2": 2,
|
||||
"/name": "Niels",
|
||||
"/nothing": null,
|
||||
"/object/currency": "USD",
|
||||
"/object/value": 42.99,
|
||||
"/pi": 3.141
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: empty objects and arrays are flattened to `#!json null`"
|
||||
@@ -47,13 +91,47 @@ Empty objects and arrays are flattened to `#!json null` and will not be reconstr
|
||||
`unflatten()` restores them as `#!json null` rather than as empty containers.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/flatten__empty.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value with an empty object and an empty array
|
||||
json j =
|
||||
{
|
||||
{"empty_object", json::object()},
|
||||
{"empty_array", json::array()},
|
||||
{"name", "Niels"}
|
||||
};
|
||||
|
||||
// call flatten()
|
||||
json flattened = j.flatten();
|
||||
std::cout << std::setw(4) << flattened << "\n\n";
|
||||
|
||||
// the empty containers cannot be restored by unflatten()
|
||||
std::cout << std::setw(4) << flattened.unflatten() << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/flatten__empty.output"
|
||||
{
|
||||
"/empty_array": null,
|
||||
"/empty_object": null,
|
||||
"/name": "Niels"
|
||||
}
|
||||
|
||||
{
|
||||
"empty_array": null,
|
||||
"empty_object": null,
|
||||
"name": "Niels"
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/flatten/" rel="canonical"><link href=../find/ rel=prev><link href=../format_as/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>flatten - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonflatten class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> flatten </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </labLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/flatten/" rel="canonical"><link href=../find/ rel=prev><link href=../format_as/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>flatten - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonflatten class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> flatten </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </labLine truncated
|
||||
</code></pre></div> <p>The function creates a <abbr title="JavaScript Object Notation">JSON</abbr> object whose keys are <abbr title="JavaScript Object Notation">JSON</abbr> pointers (see <a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901</a>) and whose values are all primitive (see <a href=../is_primitive/ ><code>is_primitive()</code></a> for more information). The original <abbr title="JavaScript Object Notation">JSON</abbr> value can be restored using the <a href=../unflatten/ ><code>unflatten()</code></a> function.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>an object that maps <abbr title="JavaScript Object Notation">JSON</abbr> pointers to primitive values</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Empty objects and arrays are flattened to <code class=highlight><span class=kc>null</span></code> and will not be reconstructed correctly by the <a href=../unflatten/ ><code>unflatten()</code></a> function.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: flatten a <abbr title="JavaScript Object Notation">JSON</abbr> object</summary> <p>The following code shows how a <abbr title="JavaScript Object Notation">JSON</abbr> object is flattened to an object whose keys consist of <abbr title="JavaScript Object Notation">JSON</abbr> pointers.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -57,7 +57,68 @@ std::string format_as(const BasicJsonType& j)
|
||||
`#!cpp "{:.>#}"`), define your own `fmt::formatter` specialization mirroring the same logic:
|
||||
|
||||
```cpp
|
||||
--8<-- "../../../tests/fmt_formatter/project/main.cpp:formatter_recipe"
|
||||
template <>
|
||||
struct fmt::formatter<nlohmann::json>
|
||||
{
|
||||
// -1 means compact output (dump()); any value >= 0 means pretty-printed
|
||||
// output with that many spaces (or indent_char) per level.
|
||||
int indent = -1;
|
||||
char indent_char = ' ';
|
||||
|
||||
constexpr auto parse(format_parse_context& ctx) -> format_parse_context::iterator
|
||||
{
|
||||
auto it = ctx.begin();
|
||||
const auto end = ctx.end();
|
||||
constexpr auto is_align = [](char c)
|
||||
{
|
||||
return c == '<' || c == '>' || c == '^';
|
||||
};
|
||||
|
||||
// [[fill] align] - repurposed here to pick a custom indent character
|
||||
if (it != end && it + 1 != end && is_align(it[1]))
|
||||
{
|
||||
indent_char = *it;
|
||||
it += 2;
|
||||
}
|
||||
else if (it != end && is_align(*it))
|
||||
{
|
||||
++it;
|
||||
}
|
||||
|
||||
// ['#'] - "alternate form", used here to request pretty-printing with a
|
||||
// default indent of 4 (overridden by an explicit width below, if given)
|
||||
if (it != end && *it == '#')
|
||||
{
|
||||
indent = 4;
|
||||
++it;
|
||||
}
|
||||
|
||||
// [width] - repurposed here to pick the indent size; a width without '#'
|
||||
// implies pretty-printing since an indent otherwise has no meaning
|
||||
if (it != end && *it >= '1' && *it <= '9')
|
||||
{
|
||||
indent = 0;
|
||||
while (it != end && *it >= '0' && *it <= '9')
|
||||
{
|
||||
indent = (indent * 10) + (*it - '0');
|
||||
++it;
|
||||
}
|
||||
}
|
||||
|
||||
if (it != end && *it != '}')
|
||||
{
|
||||
throw fmt::format_error("invalid format args for nlohmann::json");
|
||||
}
|
||||
|
||||
return it;
|
||||
}
|
||||
|
||||
auto format(const nlohmann::json& j, format_context& ctx) const
|
||||
{
|
||||
const auto dumped = j.dump(indent, indent_char);
|
||||
return fmt::format_to(ctx.out(), "{}", dumped);
|
||||
}
|
||||
};
|
||||
```
|
||||
|
||||
This recipe isn't shipped by the library itself, since doing so would make `fmt` a build dependency
|
||||
@@ -75,13 +136,30 @@ std::string format_as(const BasicJsonType& j)
|
||||
allowing argument-dependent lookup.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/format_as.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
json j = {{"one", 1}, {"two", 2}};
|
||||
|
||||
// format_as() is found via argument-dependent lookup, the same way
|
||||
// fmt::format/fmt::print would find it
|
||||
auto j_str = format_as(j);
|
||||
|
||||
std::cout << j_str << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/format_as.output"
|
||||
{"one":1,"two":2}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/format_as/" rel="canonical"><link href=../flatten/ rel=prev><link href=../from_bjdata/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>format_as - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#format_asbasic_json class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> format_as </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/format_as/" rel="canonical"><link href=../flatten/ rel=prev><link href=../from_bjdata/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>format_as - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> format_as </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
||||
<span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>format_as</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>BasicJsonType</span><span class=o>&</span><span class=w> </span><span class=n>j</span><span class=p>);</span>
|
||||
</code></pre></div> <p>This function implements the <a href="https://fmt.dev/latest/api/#formatting-user-defined-types"><code>format_as</code></a> customization point used by the <a href="https://github.com/fmtlib/fmt">{fmt}</a> library (fmtlib). It has no dependency on any <code>fmt</code> header and no effect at all unless a caller's translation unit also includes <code>fmt</code> and calls <code>fmt::format</code>/<code>fmt::print</code> on a <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>BasicJsonType</code></dt> <dd>a specialization of <a href=../ ><code>basic_json</code></a></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>string containing the serialization of the <abbr title="JavaScript Object Notation">JSON</abbr> value (same as <a href=../dump/ ><code>dump()</code></a>)</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> if a string stored inside the <abbr title="JavaScript Object Notation">JSON</abbr> value is not <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoded</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=possible-implementation>Possible implementation<a class=headerlink href=#possible-implementation title="Permanent link">¶</a></h2> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=w> </span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=o>></span>
|
||||
<span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>format_as</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>BasicJsonType</span><span class=o>&</span><span class=w> </span><span class=n>j</span><span class=p>)</span>
|
||||
|
||||
@@ -96,13 +96,37 @@ Linear in the size of the input.
|
||||
The example shows the deserialization of a byte vector in BJData format to a JSON value.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/from_bjdata.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create byte vector
|
||||
std::vector<std::uint8_t> v = {0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61,
|
||||
0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68,
|
||||
0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D
|
||||
};
|
||||
|
||||
// deserialize it with BJData
|
||||
json j = json::from_bjdata(v);
|
||||
|
||||
// print the deserialized JSON value
|
||||
std::cout << std::setw(2) << j << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/from_bjdata.output"
|
||||
{
|
||||
"compact": true,
|
||||
"schema": 0
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -124,7 +148,8 @@ Linear in the size of the input.
|
||||
!!! warning "Deprecation"
|
||||
|
||||
- Overload (2) replaces calls to `from_bjdata` with a pointer and a length as first two parameters, which has been
|
||||
deprecated in version 3.13.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
deprecated in version 3.13.0. In version 4.0.0, this overload
|
||||
will be deleted (`= delete`) rather than removed. Please replace all calls like
|
||||
`#!cpp from_bjdata(ptr, len, ...);` with `#!cpp from_bjdata(ptr, ptr+len, ...);`.
|
||||
|
||||
You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_bjdata/" rel="canonical"><link href=../format_as/ rel=prev><link href=../from_bon8/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_bjdata - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_bjdata </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_bjdata/" rel="canonical"><link href=../format_as/ rel=prev><link href=../from_bon8/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_bjdata - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_bjdata class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_bjdata </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5Line truncated
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>></span>
|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=n>from_bjdata</span><span class=p>(</span><span class=n>InputType</span><span class=o>&&</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>strict</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>,</span>
|
||||
@@ -34,4 +34,4 @@
|
||||
<span class=w> </span><span class=nt>"compact"</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_bjdata/ >to_bjdata</a> create a <abbr title="Binary JData">BJData</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ >from_cbor</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ >from_msgpack</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ >from_ubjson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.11.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_bjdata</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_bjdata</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bjdata</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 20:11:34 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_bjdata/ >to_bjdata</a> create a <abbr title="Binary JData">BJData</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ >from_cbor</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ >from_msgpack</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ >from_ubjson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.11.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_bjdata</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>. In version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, this overload will be deleted (<code>= delete</code>) rather than removed. Please replace all calls like <code class=highlight><span class=n>from_bjdata</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bjdata</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <fLine truncated
|
||||
@@ -133,6 +133,6 @@ Output:
|
||||
|
||||
Deprecation
|
||||
|
||||
- Overload (2) replaces calls to `from_bjdata` with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 unreleased. This overload will be removed in version 4.0.0. Please replace all calls like `from_bjdata(ptr, len, ...);` with `from_bjdata(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_bjdata` with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 unreleased. In version 4.0.0 unreleased, this overload will be deleted (`= delete`) rather than removed. Please replace all calls like `from_bjdata(ptr, len, ...);` with `from_bjdata(ptr, ptr+len, ...);`.
|
||||
|
||||
You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated function.
|
||||
@@ -85,13 +85,39 @@ Linear in the size of the input.
|
||||
The example shows the deserialization of a byte vector in BON8 format to a JSON value.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/from_bon8.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create byte vector
|
||||
std::vector<std::uint8_t> v = {0x89, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63, 0x74,
|
||||
0xf9, 0x66, 0x6f, 0x72, 0x6d, 0x61, 0x74, 0xff,
|
||||
0x42, 0x4f, 0x4e, 0x38, 0xff, 0x73, 0x63, 0x68,
|
||||
0x65, 0x6d, 0x61, 0x90
|
||||
};
|
||||
|
||||
// deserialize it with BON8
|
||||
json j = json::from_bon8(v);
|
||||
|
||||
// print the deserialized JSON value
|
||||
std::cout << std::setw(2) << j << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/from_bon8.output"
|
||||
{
|
||||
"compact": true,
|
||||
"format": "BON8",
|
||||
"schema": 0
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -110,7 +136,8 @@ Linear in the size of the input.
|
||||
!!! warning "Deprecation"
|
||||
|
||||
- Overload (2) replaces calls to `from_bon8` with a pointer and a length as first two parameters, which has been
|
||||
deprecated in version 3.13.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
deprecated in version 3.13.0. In version 4.0.0, this overload
|
||||
will be deleted (`= delete`) rather than removed. Please replace all calls like
|
||||
`#!cpp from_bon8(ptr, len, ...);` with `#!cpp from_bon8(ptr, ptr+len, ...);`.
|
||||
|
||||
You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_bon8/" rel="canonical"><link href=../from_bjdata/ rel=prev><link href=../from_bson/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_bon8 - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_bon8/" rel="canonical"><link href=../from_bjdata/ rel=prev><link href=../from_bson/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_bon8 - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_bon8 </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>></span>
|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=n>from_bon8</span><span class=p>(</span><span class=n>InputType</span><span class=o>&&</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>strict</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>,</span>
|
||||
@@ -34,4 +34,4 @@
|
||||
<span class=w> </span><span class=nt>"format"</span><span class=p>:</span><span class=w> </span><span class=s2>"BON8"</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_bon8/ >to_bon8</a> create a <abbr title="Binary Object Notation 8">BON8</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ >from_cbor</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ >from_msgpack</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ >from_ubjson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_bon8</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_bon8</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bon8</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 20:11:34 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9Line truncated
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||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_bon8/ >to_bon8</a> create a <abbr title="Binary Object Notation 8">BON8</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ >from_cbor</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ >from_msgpack</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ >from_ubjson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_bon8</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>. In version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, this overload will be deleted (<code>= delete</code>) rather than removed. Please replace all calls like <code class=highlight><span class=n>from_bon8</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bon8</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.Line truncated
|
||||
@@ -126,6 +126,6 @@ Output:
|
||||
|
||||
Deprecation
|
||||
|
||||
- Overload (2) replaces calls to `from_bon8` with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 unreleased. This overload will be removed in version 4.0.0. Please replace all calls like `from_bon8(ptr, len, ...);` with `from_bon8(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_bon8` with a pointer and a length as first two parameters, which has been deprecated in version 3.13.0 unreleased. In version 4.0.0 unreleased, this overload will be deleted (`= delete`) rather than removed. Please replace all calls like `from_bon8(ptr, len, ...);` with `from_bon8(ptr, ptr+len, ...);`.
|
||||
|
||||
You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated function.
|
||||
@@ -97,13 +97,38 @@ Linear in the size of the input.
|
||||
The example shows the deserialization of a byte vector in BSON format to a JSON value.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/from_bson.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create byte vector
|
||||
std::vector<std::uint8_t> v = {0x1b, 0x00, 0x00, 0x00, 0x08, 0x63, 0x6f, 0x6d,
|
||||
0x70, 0x61, 0x63, 0x74, 0x00, 0x01, 0x10, 0x73,
|
||||
0x63, 0x68, 0x65, 0x6d, 0x61, 0x00, 0x00, 0x00,
|
||||
0x00, 0x00, 0x00
|
||||
};
|
||||
|
||||
// deserialize it with BSON
|
||||
json j = json::from_bson(v);
|
||||
|
||||
// print the deserialized JSON value
|
||||
std::cout << std::setw(2) << j << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/from_bson.output"
|
||||
{
|
||||
"compact": true,
|
||||
"schema": 0
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -126,7 +151,8 @@ Linear in the size of the input.
|
||||
!!! warning "Deprecation"
|
||||
|
||||
- Overload (2) replaces calls to `from_bson` with a pointer and a length as first two parameters, which has been
|
||||
deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
deprecated in version 3.8.0. In version 4.0.0, this overload
|
||||
will be deleted (`= delete`) rather than removed. Please replace all calls like
|
||||
`#!cpp from_bson(ptr, len, ...);` with `#!cpp from_bson(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_bson` with a pair of iterators as their first parameter, which has been
|
||||
deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_bson/" rel="canonical"><link href=../from_bon8/ rel=prev><link href=../from_cbor/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_bson - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_bson class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_bson </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_bson/" rel="canonical"><link href=../from_bon8/ rel=prev><link href=../from_cbor/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_bson - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_bson class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_bson </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/Line truncated
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>></span>
|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=n>from_bson</span><span class=p>(</span><span class=n>InputType</span><span class=o>&&</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>strict</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>,</span>
|
||||
@@ -35,4 +35,4 @@
|
||||
<span class=w> </span><span class=nt>"compact"</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="http://bsonspec.org/spec.html"><abbr title="Binary JSON">BSON</abbr> specification</a></li> <li><a href=../to_bson/ >to_bson</a> for the analogous serialization</li> <li><a href=../from_cbor/ >from_cbor</a> for the related <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ >from_msgpack</a> for the related MessagePack format</li> <li><a href=../from_ubjson/ >from_ubjson</a> for the related <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> for the related <abbr title="Binary JData">BJData</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> for the related <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.4.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_bson</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_bson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> <li>Overload (2) replaces calls to <code>from_bson</code> with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_bson</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 10:13:49 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));targetLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="http://bsonspec.org/spec.html"><abbr title="Binary JSON">BSON</abbr> specification</a></li> <li><a href=../to_bson/ >to_bson</a> for the analogous serialization</li> <li><a href=../from_cbor/ >from_cbor</a> for the related <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ >from_msgpack</a> for the related MessagePack format</li> <li><a href=../from_ubjson/ >from_ubjson</a> for the related <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> for the related <abbr title="Binary JData">BJData</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> for the related <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.4.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_bson</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. In version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, this overload will be deleted (<code>= delete</code>) rather than removed. Please replace all calls like <code class=highlight><span class=n>from_bson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> <li>Overload (2) replaces calls to <code>from_bson</code> with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_bson</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_bson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:51 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){Line truncated
|
||||
@@ -135,7 +135,7 @@ Output:
|
||||
|
||||
Deprecation
|
||||
|
||||
- Overload (2) replaces calls to `from_bson` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_bson(ptr, len, ...);` with `from_bson(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_bson` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. In version 4.0.0 unreleased, this overload will be deleted (`= delete`) rather than removed. Please replace all calls like `from_bson(ptr, len, ...);` with `from_bson(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_bson` with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_bson({ptr, ptr+len}, ...);` with `from_bson(ptr, ptr+len, ...);`.
|
||||
|
||||
You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated function.
|
||||
|
||||
@@ -103,13 +103,37 @@ Linear in the size of the input.
|
||||
The example shows the deserialization of a byte vector in CBOR format to a JSON value.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/from_cbor.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create byte vector
|
||||
std::vector<std::uint8_t> v = {0xa2, 0x67, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63,
|
||||
0x74, 0xf5, 0x66, 0x73, 0x63, 0x68, 0x65, 0x6d,
|
||||
0x61, 0x00
|
||||
};
|
||||
|
||||
// deserialize it with CBOR
|
||||
json j = json::from_cbor(v);
|
||||
|
||||
// print the deserialized JSON value
|
||||
std::cout << std::setw(2) << j << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/from_cbor.output"
|
||||
{
|
||||
"compact": true,
|
||||
"schema": 0
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -135,7 +159,8 @@ Linear in the size of the input.
|
||||
!!! warning "Deprecation"
|
||||
|
||||
- Overload (2) replaces calls to `from_cbor` with a pointer and a length as first two parameters, which has been
|
||||
deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
deprecated in version 3.8.0. In version 4.0.0, this overload
|
||||
will be deleted (`= delete`) rather than removed. Please replace all calls like
|
||||
`#!cpp from_cbor(ptr, len, ...);` with `#!cpp from_cbor(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_cbor` with a pair of iterators as their first parameter, which has been
|
||||
deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_cbor/" rel="canonical"><link href=../from_bson/ rel=prev><link href=../from_msgpack/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_cbor - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_cbor class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_cbor </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_cbor/" rel="canonical"><link href=../from_bson/ rel=prev><link href=../from_msgpack/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_cbor - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_cbor class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_cbor </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 Line truncated
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>></span>
|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=n>from_cbor</span><span class=p>(</span><span class=n>InputType</span><span class=o>&&</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>strict</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>,</span>
|
||||
@@ -37,4 +37,4 @@
|
||||
<span class=w> </span><span class=nt>"compact"</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_cbor/ >to_cbor</a> create a <abbr title="Concise Binary Object Representation">CBOR</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_msgpack/ >from_msgpack</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ >from_ubjson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.9.</li> <li>Parameter <code>start_index</code> since version 2.1.1.</li> <li>Changed to consume input adapters, removed <code>start_index</code> parameter, and added <code>strict</code> parameter in version 3.0.0.</li> <li>Added <code>allow_exceptions</code> parameter in version 3.2.0.</li> <li>Added <code>tag_handler</code> parameter in version 3.9.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_cbor</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_cbor</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_cbor</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> <li>Overload (2) replaces calls to <code>from_cbor</code> with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_cbor</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_cbor</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 Line truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_cbor/ >to_cbor</a> create a <abbr title="Concise Binary Object Representation">CBOR</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_msgpack/ >from_msgpack</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ >from_ubjson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.9.</li> <li>Parameter <code>start_index</code> since version 2.1.1.</li> <li>Changed to consume input adapters, removed <code>start_index</code> parameter, and added <code>strict</code> parameter in version 3.0.0.</li> <li>Added <code>allow_exceptions</code> parameter in version 3.2.0.</li> <li>Added <code>tag_handler</code> parameter in version 3.9.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_cbor</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. In version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, this overload will be deleted (<code>= delete</code>) rather than removed. Please replace all calls like <code class=highlight><span class=n>from_cbor</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_cbor</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> <li>Overload (2) replaces calls to <code>from_cbor</code> with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_cbor</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_cbor</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1Line truncated
|
||||
@@ -141,7 +141,7 @@ Output:
|
||||
|
||||
Deprecation
|
||||
|
||||
- Overload (2) replaces calls to `from_cbor` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_cbor(ptr, len, ...);` with `from_cbor(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_cbor` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. In version 4.0.0 unreleased, this overload will be deleted (`= delete`) rather than removed. Please replace all calls like `from_cbor(ptr, len, ...);` with `from_cbor(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_cbor` with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_cbor({ptr, ptr+len}, ...);` with `from_cbor(ptr, ptr+len, ...);`.
|
||||
|
||||
You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated function.
|
||||
|
||||
@@ -96,13 +96,37 @@ Linear in the size of the input.
|
||||
The example shows the deserialization of a byte vector in MessagePack format to a JSON value.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/from_msgpack.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create byte vector
|
||||
std::vector<std::uint8_t> v = {0x82, 0xa7, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63,
|
||||
0x74, 0xc3, 0xa6, 0x73, 0x63, 0x68, 0x65, 0x6d,
|
||||
0x61, 0x00
|
||||
};
|
||||
|
||||
// deserialize it with MessagePack
|
||||
json j = json::from_msgpack(v);
|
||||
|
||||
// print the deserialized JSON value
|
||||
std::cout << std::setw(2) << j << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/from_msgpack.output"
|
||||
{
|
||||
"compact": true,
|
||||
"schema": 0
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -127,7 +151,8 @@ Linear in the size of the input.
|
||||
!!! warning "Deprecation"
|
||||
|
||||
- Overload (2) replaces calls to `from_msgpack` with a pointer and a length as first two parameters, which has been
|
||||
deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
deprecated in version 3.8.0. In version 4.0.0, this overload
|
||||
will be deleted (`= delete`) rather than removed. Please replace all calls like
|
||||
`#!cpp from_msgpack(ptr, len, ...);` with `#!cpp from_msgpack(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_msgpack` with a pair of iterators as their first parameter, which has been
|
||||
deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_msgpack/" rel="canonical"><link href=../from_cbor/ rel=prev><link href=../from_ubjson/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_msgpack - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_msgpack class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_msgpack </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to 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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_msgpack/" rel="canonical"><link href=../from_cbor/ rel=prev><link href=../from_ubjson/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_msgpack - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_msgpack class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_msgpack </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.Line truncated
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>></span>
|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=n>from_msgpack</span><span class=p>(</span><span class=n>InputType</span><span class=o>&&</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>strict</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>,</span>
|
||||
@@ -34,4 +34,4 @@
|
||||
<span class=w> </span><span class=nt>"compact"</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_msgpack/ >to_msgpack</a> create a MessagePack serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ >from_cbor</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ >from_ubjson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.9.</li> <li>Parameter <code>start_index</code> since version 2.1.1.</li> <li>Changed to consume input adapters, removed <code>start_index</code> parameter, and added <code>strict</code> parameter in version 3.0.0.</li> <li>Added <code>allow_exceptions</code> parameter in version 3.2.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_msgpack</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_msgpack</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_msgpack</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> <li>Overload (2) replaces calls to <code>from_msgpack</code> with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_msgpack</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_msgpack</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2zLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_msgpack/ >to_msgpack</a> create a MessagePack serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ >from_cbor</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_ubjson/ >from_ubjson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Universal Binary JSON">UBJSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.9.</li> <li>Parameter <code>start_index</code> since version 2.1.1.</li> <li>Changed to consume input adapters, removed <code>start_index</code> parameter, and added <code>strict</code> parameter in version 3.0.0.</li> <li>Added <code>allow_exceptions</code> parameter in version 3.2.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_msgpack</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. In version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, this overload will be deleted (<code>= delete</code>) rather than removed. Please replace all calls like <code class=highlight><span class=n>from_msgpack</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_msgpack</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> <li>Overload (2) replaces calls to <code>from_msgpack</code> with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_msgpack</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_msgpack</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM1Line truncated
|
||||
@@ -135,7 +135,7 @@ Output:
|
||||
|
||||
Deprecation
|
||||
|
||||
- Overload (2) replaces calls to `from_msgpack` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_msgpack(ptr, len, ...);` with `from_msgpack(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_msgpack` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. In version 4.0.0 unreleased, this overload will be deleted (`= delete`) rather than removed. Please replace all calls like `from_msgpack(ptr, len, ...);` with `from_msgpack(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_msgpack` with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_msgpack({ptr, ptr+len}, ...);` with `from_msgpack(ptr, ptr+len, ...);`.
|
||||
|
||||
You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated function.
|
||||
|
||||
@@ -96,13 +96,37 @@ Linear in the size of the input.
|
||||
The example shows the deserialization of a byte vector in UBJSON format to a JSON value.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/from_ubjson.cpp"
|
||||
#include <iostream>
|
||||
#include <iomanip>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create byte vector
|
||||
std::vector<std::uint8_t> v = {0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61,
|
||||
0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68,
|
||||
0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D
|
||||
};
|
||||
|
||||
// deserialize it with UBJSON
|
||||
json j = json::from_ubjson(v);
|
||||
|
||||
// print the deserialized JSON value
|
||||
std::cout << std::setw(2) << j << std::endl;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/from_ubjson.output"
|
||||
{
|
||||
"compact": true,
|
||||
"schema": 0
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -125,7 +149,8 @@ Linear in the size of the input.
|
||||
!!! warning "Deprecation"
|
||||
|
||||
- Overload (2) replaces calls to `from_ubjson` with a pointer and a length as first two parameters, which has been
|
||||
deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
deprecated in version 3.8.0. In version 4.0.0, this overload
|
||||
will be deleted (`= delete`) rather than removed. Please replace all calls like
|
||||
`#!cpp from_ubjson(ptr, len, ...);` with `#!cpp from_ubjson(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_ubjson` with a pair of iterators as their first parameter, which has been
|
||||
deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_ubjson/" rel="canonical"><link href=../from_msgpack/ rel=prev><link href=../front/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_ubjson - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_ubjson class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_ubjson </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 Line truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/from_ubjson/" rel="canonical"><link href=../from_msgpack/ rel=prev><link href=../front/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_ubjson - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfrom_ubjson class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_ubjson </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 Line truncated
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>></span>
|
||||
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=n>from_ubjson</span><span class=p>(</span><span class=n>InputType</span><span class=o>&&</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>strict</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>,</span>
|
||||
@@ -34,4 +34,4 @@
|
||||
<span class=w> </span><span class=nt>"compact"</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_ubjson/ >to_ubjson</a> create a <abbr title="Universal Binary JSON">UBJSON</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ >from_cbor</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ >from_msgpack</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.1.0.</li> <li>Added <code>allow_exceptions</code> parameter in version 3.2.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_ubjson</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_ubjson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_ubjson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> <li>Overload (2) replaces calls to <code>from_ubjson</code> with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_ubjson</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_ubjson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 10:13:49 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_ubjson/ >to_ubjson</a> create a <abbr title="Universal Binary JSON">UBJSON</abbr> serialization of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../from_cbor/ >from_cbor</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> <li><a href=../from_msgpack/ >from_msgpack</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in MessagePack format</li> <li><a href=../from_bson/ >from_bson</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JSON">BSON</abbr> format</li> <li><a href=../from_bjdata/ >from_bjdata</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary JData">BJData</abbr> format</li> <li><a href=../from_bon8/ >from_bon8</a> create a <abbr title="JavaScript Object Notation">JSON</abbr> value from an input in <abbr title="Binary Object Notation 8">BON8</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.1.0.</li> <li>Added <code>allow_exceptions</code> parameter in version 3.2.0.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <code>error_handler</code> parameter in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <ul> <li>Overload (2) replaces calls to <code>from_ubjson</code> with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. In version 4.0.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, this overload will be deleted (<code>= delete</code>) rather than removed. Please replace all calls like <code class=highlight><span class=n>from_ubjson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_ubjson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> <li>Overload (2) replaces calls to <code>from_ubjson</code> with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>from_ubjson</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>from_ubjson</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</li> </ul> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localizedLine truncated
|
||||
@@ -134,7 +134,7 @@ Output:
|
||||
|
||||
Deprecation
|
||||
|
||||
- Overload (2) replaces calls to `from_ubjson` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_ubjson(ptr, len, ...);` with `from_ubjson(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_ubjson` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. In version 4.0.0 unreleased, this overload will be deleted (`= delete`) rather than removed. Please replace all calls like `from_ubjson(ptr, len, ...);` with `from_ubjson(ptr, ptr+len, ...);`.
|
||||
- Overload (2) replaces calls to `from_ubjson` with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_ubjson({ptr, ptr+len}, ...);` with `from_ubjson(ptr, ptr+len, ...);`.
|
||||
|
||||
You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated function.
|
||||
|
||||
+37
-2
@@ -39,13 +39,48 @@ Constant.
|
||||
The following code shows an example for `front()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/front.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON values
|
||||
json j_null;
|
||||
json j_boolean = true;
|
||||
json j_number_integer = 17;
|
||||
json j_number_float = 23.42;
|
||||
json j_object = {{"one", 1}, {"two", 2}};
|
||||
json j_object_empty(json::value_t::object);
|
||||
json j_array = {1, 2, 4, 8, 16};
|
||||
json j_array_empty(json::value_t::array);
|
||||
json j_string = "Hello, world";
|
||||
|
||||
// call front()
|
||||
//std::cout << j_null.front() << '\n'; // would throw
|
||||
std::cout << j_boolean.front() << '\n';
|
||||
std::cout << j_number_integer.front() << '\n';
|
||||
std::cout << j_number_float.front() << '\n';
|
||||
std::cout << j_object.front() << '\n';
|
||||
//std::cout << j_object_empty.front() << '\n'; // undefined behavior
|
||||
std::cout << j_array.front() << '\n';
|
||||
//std::cout << j_array_empty.front() << '\n'; // undefined behavior
|
||||
std::cout << j_string.front() << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/front.output"
|
||||
true
|
||||
17
|
||||
23.42
|
||||
1
|
||||
1
|
||||
"Hello, world"
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/front/" rel="canonical"><link href=../from_ubjson/ rel=prev><link href=../get/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>front - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfront class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> front </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <diLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/front/" rel="canonical"><link href=../from_ubjson/ rel=prev><link href=../get/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>front - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonfront class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> front </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <diLine truncated
|
||||
<span class=n>const_reference</span><span class=w> </span><span class=nf>front</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
</code></pre></div> <p>Returns a reference to the first element in the container. For a <abbr title="JavaScript Object Notation">JSON</abbr> container <code class=highlight><span class=n>c</span></code>, the expression <code class=highlight><span class=n>c</span><span class=p>.</span><span class=n>front</span><span class=p>()</span></code> is equivalent to <code class=highlight><span class=o>*</span><span class=n>c</span><span class=p>.</span><span class=n>begin</span><span class=p>()</span></code>.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>In the case of a structured type (array or object), a reference to the first element is returned. In the case of number, string, boolean, or binary values, a reference to the value is returned.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>If the <abbr title="JavaScript Object Notation">JSON</abbr> value is <code class=highlight><span class=kc>null</span></code>, exception <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator214><code>invalid_iterator.214</code></a> is thrown.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition info"> <p class=admonition-title>Precondition</p> <p>The array or object must not be empty. Calling <code>front</code> on an empty array or object yields undefined behavior.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>front()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
+109
-6
@@ -138,13 +138,74 @@ overload (3).
|
||||
associative containers such as `std::map<std::string, json>`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/get__ValueType_const.cpp"
|
||||
#include <iostream>
|
||||
#include <map>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value with different types
|
||||
json json_types =
|
||||
{
|
||||
{"boolean", true},
|
||||
{
|
||||
"number", {
|
||||
{"integer", 42},
|
||||
{"floating-point", 17.23}
|
||||
}
|
||||
},
|
||||
{"string", "Hello, world!"},
|
||||
{"array", {1, 2, 3, 4, 5}},
|
||||
{"null", nullptr}
|
||||
};
|
||||
|
||||
// use explicit conversions
|
||||
auto v1 = json_types["boolean"].get<bool>();
|
||||
auto v2 = json_types["number"]["integer"].get<int>();
|
||||
auto v3 = json_types["number"]["integer"].get<short>();
|
||||
auto v4 = json_types["number"]["floating-point"].get<float>();
|
||||
auto v5 = json_types["number"]["floating-point"].get<int>();
|
||||
auto v6 = json_types["string"].get<std::string>();
|
||||
auto v7 = json_types["array"].get<std::vector<short>>();
|
||||
auto v8 = json_types.get<std::map<std::string, json>>();
|
||||
|
||||
// print the conversion results
|
||||
std::cout << v1 << '\n';
|
||||
std::cout << v2 << ' ' << v3 << '\n';
|
||||
std::cout << v4 << ' ' << v5 << '\n';
|
||||
std::cout << v6 << '\n';
|
||||
|
||||
for (auto i : v7)
|
||||
{
|
||||
std::cout << i << ' ';
|
||||
}
|
||||
std::cout << "\n\n";
|
||||
|
||||
for (auto i : v8)
|
||||
{
|
||||
std::cout << i.first << ": " << i.second << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/get__ValueType_const.output"
|
||||
1
|
||||
42 42
|
||||
17.23 17
|
||||
Hello, world!
|
||||
1 2 3 4 5
|
||||
|
||||
array: [1,2,3,4,5]
|
||||
boolean: true
|
||||
null: null
|
||||
number: {"floating-point":17.23,"integer":42}
|
||||
string: "Hello, world!"
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (2) explicit conversion to another `basic_json` specialization"
|
||||
@@ -152,13 +213,32 @@ overload (3).
|
||||
The example below shows how a `json` value is converted to an `ordered_json` value using `get<BasicJsonType>()`.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/get__BasicJsonType.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using ordered_json = nlohmann::ordered_json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
json j = {{"one", 1}, {"two", 2}, {"three", 3}};
|
||||
|
||||
// convert to a different basic_json specialization
|
||||
ordered_json oj = j.get<ordered_json>();
|
||||
|
||||
std::cout << j << '\n';
|
||||
std::cout << oj << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/get__BasicJsonType.output"
|
||||
{"one":1,"three":3,"two":2}
|
||||
{"one":1,"three":3,"two":2}
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (3) explicit pointer access to the stored value"
|
||||
@@ -167,13 +247,36 @@ overload (3).
|
||||
conversions are made and a `#cpp nullptr` is returned if the value and the requested pointer type does not match.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/get__PointerType.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON number
|
||||
json value = 17;
|
||||
|
||||
// explicitly getting pointers
|
||||
auto p1 = value.get<const json::number_integer_t*>();
|
||||
auto p2 = value.get<json::number_integer_t*>();
|
||||
auto p3 = value.get<json::number_integer_t* const>();
|
||||
auto p4 = value.get<const json::number_integer_t* const>();
|
||||
auto p5 = value.get<json::number_float_t*>();
|
||||
|
||||
// print the pointees
|
||||
std::cout << *p1 << ' ' << *p2 << ' ' << *p3 << ' ' << *p4 << '\n';
|
||||
std::cout << std::boolalpha << (p5 == nullptr) << '\n';
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/get__PointerType.output"
|
||||
17 17 17 17
|
||||
true
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
@@ -1,4 +1,4 @@
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/get/" rel="canonical"><link href=../front/ rel=prev><link href=../get_allocator/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>get - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonget class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> get </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div clLine truncated
|
||||
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/get/" rel="canonical"><link href=../front/ rel=prev><link href=../get_allocator/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>get - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonget class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> get </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div clLine truncated
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>ValueType</span><span class=o>></span>
|
||||
<span class=n>ValueType</span><span class=w> </span><span class=n>get</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span>
|
||||
<span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=n>JSONSerializer</span><span class=o><</span><span class=n>ValueType</span><span class=o>>::</span><span class=n>from_json</span><span class=p>(</span>
|
||||
|
||||
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