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<span class=n>basic_json_view</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>string_view_t</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=n>basic_json_view</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=kt>char</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=n>basic_json_view</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>string_t</span><span class=o>&amp;</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>
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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_view/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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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> 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" 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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> </label> <divLine truncated
</code></pre></div> <p>Returns the last element of an array, the last member value of an object, or the value itself if it is primitive (as for <a href=../../basic_json/back/ ><code>BasicJsonType::back()</code></a>, a primitive value is a range of one element).</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The last element or member value. For a primitive value (number, string, boolean), the value itself.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: there are no changes to the view or the document it refers to.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator214><code>invalid_iterator.214</code></a> if the view is <a href=../is_null/ >null</a> or <a href=../is_discarded/ >discarded</a>, or if it is an empty array or object.</p> <p>This exception does not carry a <a href=../../macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> path: the view has no <code>BasicJsonType</code> value to point at, so the exception is created without one, even if <code>BasicJsonType</code> was built with <code>JSON_DIAGNOSTICS</code> enabled.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of the array or object: unlike <a href=../front/ ><code>front()</code></a>, which only ever looks at the first element, <code>back()</code> has to walk every element to find where they end, since elements are not a fixed size in the index.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Unlike <a href=../../basic_json/back/ ><code>BasicJsonType::back()</code></a>, which has undefined behavior for an empty array or object, <code>back()</code> throws <code>invalid_iterator.214</code> for an empty array, an empty object, a null value, or a discarded view.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below reads only the final status of a build log with <code>back()</code>. Even though <code>back()</code> is linear in the number of events (unlike <a href=../front/ ><code>front()</code></a>, which is constant), it still avoids building a <code>BasicJsonType</code> value for the events that are not needed.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
@@ -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_view/basic_json_view/" rel="canonical"><link href=../ 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>(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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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 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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_view/basic_json_view/" rel="canonical"><link href=../ 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>(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_json_viewbasic_json_view 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 9.5Line truncated
</code></pre></div> <p>Creates an invalid (discarded) view: <a href=../type/ ><code>type()</code></a> is <code class=highlight><span class=n>value_t</span><span class=o>::</span><span class=n>discarded</span></code> and <a href=../is_discarded/ ><code>is_discarded()</code></a> is <code class=highlight><span class=nb>true</span></code>.</p> <p>This is the only constructor a caller can use directly. Every other view is obtained from a <a href=../../basic_json_document/ ><code>basic_json_document</code></a>, via <a href=../../basic_json_document/root/ ><code>root()</code></a> or by navigating into a container with <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../front/ ><code>front</code></a>, <a href=../back/ ><code>back</code></a>, <a href=../find/ ><code>find</code></a>, or iteration.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this constructor never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p><code>basic_json_view</code> is trivially copyable (it holds two pointers), so a default-constructed view can be used as a placeholder for "no value yet" and later be assigned a real view.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows the default constructor and that a <code>basic_json_view</code> is a small, copyable handle.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
+1 -1
View File
@@ -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_view/begin/" rel="canonical"><link href=../back/ 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>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 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</code></pre></div> <p>Returns an iterator to the first element of an array, or the first member value of an object, in <strong>document order</strong> -- the order the values appear in the source text, not sorted by key. A primitive value iterates as a range of one element (itself), and a <code class=highlight><span class=kc>null</span></code> value or a <a href=../is_discarded/ >discarded</a> view iterates as an empty range.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Iterator to the first element.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>For an object, iteration visits <strong>every</strong> member, including all occurrences of a duplicate key -- unlike <a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../find/ ><code>find</code></a>, and <a href=../contains/ ><code>contains</code></a>, which all resolve to the <em>first</em> member with a given key. See the <a href=../operator%5B%5D/#notes>Notes on duplicate keys</a> of <code>operator[]</code>.</p> <p>Because objects are iterated in document order rather than sorted by key, the order seen here can differ from what iterating the <a href=../materialize/ ><code>materialize()</code></a>d <code>BasicJsonType</code> value would produce: a <code class=highlight><span class=n>basic_json</span></code> object (<code>std::map</code>-backed by default) sorts its keys, while a view does not.</p> <p>An <code>ordered_json</code> value also keeps document order, but it keeps only one entry per key: as <code>parse()</code> does, it keeps the <em>last</em> value, at the position of the key's <em>first</em> occurrence. The view, in contrast, visits every member, including the duplicates.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below iterates a log record's members with <code>begin()</code>/<a href=../end/ ><code>end()</code></a> and prints them in the order they were written. Materializing the record into a <code>BasicJsonType</code> object and iterating that would instead print the members sorted by key.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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</code></pre></div> <p>Returns an iterator to the first element, in <a href=../begin/ >document order</a>. Equivalent to <a href=../begin/ ><code>begin()</code></a>: a view is always read-only, so <code class=highlight><span class=n>const_iterator</span></code> and <code class=highlight><span class=n>iterator</span></code> are the same type, and <code>cbegin()</code> exists only so that generic code that expects a <code>cbegin()</code>/<code>cend()</code> pair works with a view too.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Iterator to the first element; identical to what <a href=../begin/ ><code>begin()</code></a> returns.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below sums many measurements with <code>std::accumulate</code>, using <code>cbegin()</code>/<a href=../cend/ ><code>cend()</code></a> as the range -- the same way it would for any standard container -- without ever materializing the whole array into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;numeric&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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</code></pre></div> <p>Returns an iterator to one past the last element, in <a href=../begin/ >document order</a>. Equivalent to <a href=../end/ ><code>end()</code></a>: a view is always read-only, so <code class=highlight><span class=n>const_iterator</span></code> and <code class=highlight><span class=n>iterator</span></code> are the same type, and <code>cend()</code> exists only so that generic code that expects a <code>cbegin()</code>/<code>cend()</code> pair works with a view too.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Iterator one past the last element; identical to what <a href=../end/ ><code>end()</code></a> returns.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below checks that every record of a batch is an object with <code>std::all_of</code>, using <a href=../cbegin/ ><code>cbegin()</code></a>/<code>cend()</code> as the range -- the same way it would for any standard container -- before materializing any record of the batch.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;algorithm&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/contains/" rel="canonical"><link href=../cend/ 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 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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> 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 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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=kt>bool</span><span class=w> </span><span class=nf>contains</span><span class=p>(</span><span class=n>string_view_t</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=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=kt>char</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=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>string_t</span><span class=o>&amp;</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>
+1 -1
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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/basic_json_view/count/" rel="canonical"><link href=../contains/ 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>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 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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_view/count/" rel="canonical"><link href=../contains/ 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>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 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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> 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 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<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=kt>char</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=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=n>string_t</span><span class=o>&amp;</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> <p>Returns the number of members with key <code>key</code> if the value is an object, <code class=highlight><span class=mi>0</span></code> otherwise. Members with a repeated key are all counted.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</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">&para;</a></h2> <p>the number of members of the object with key <code>key</code> (duplicates included), or <code class=highlight><span class=mi>0</span></code> if the value is not an object or has no such member.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the number of members: unlike the lookup functions, <code>count()</code> does not stop at the first match, because it has to count every member with the key. Members are compared one after another, in document order. Each comparison first checks the key's length -- already known from the index, without reading the key bytes -- before comparing its content. The hash index of the keys of objects with 128 or more members does not help here, since every member is visited.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This method always returns <code class=highlight><span class=mi>0</span></code> when the value is not an object -- including a <a href=../is_discarded/ >discarded</a> view.</p> <p>If the source text repeats a key, <code>count()</code> returns more than <code class=highlight><span class=mi>1</span></code> for it, even though the <a href=../materialize/ >materialized</a> value (like the result of <code>parse()</code>) would have only one member with that key. Hence <code class=highlight><span class=n>count</span><span class=p>(</span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=o>&gt;</span><span class=w> </span><span class=mi>1</span></code> detects duplicate keys. This is unlike the lookup functions (<a href=../operator%5B%5D/ ><code>operator[]</code></a>, <a href=../at/ ><code>at</code></a>, <a href=../find/ ><code>find</code></a>, <a href=../contains/ ><code>contains</code></a>), which resolve to the <em>first</em> member; see the <a href=../operator%5B%5D/#notes>Notes on duplicate keys</a> of <code>operator[]</code>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below validates that every transaction of a batch carries exactly one <code>amount</code> field, using <code>count()</code> before deciding whether to materialize a transaction at all. It reports a transaction with no <code>amount</code> field and one with a duplicated <code>amount</code> field.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
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<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>number_format</span><span class=w> </span><span class=n>numbers</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>number_format</span><span class=o>::</span><span class=n>shortest</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
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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_view/empty/" rel="canonical"><link href=../dump/ 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 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_json_viewempty 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> 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 whether <a href=../size/ ><code>size()</code></a> is <code>0</code>, as <a href=../../basic_json/empty/ ><code>BasicJsonType::empty()</code></a> would for the same value.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The return value depends on the type 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>discarded</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>object</td> <td><code class=highlight><span class=n>object_t</span><span class=o>::</span><span class=n>empty</span><span class=p>()</span></code></td> </tr> <tr> <td>array</td> <td><code class=highlight><span class=n>array_t</span><span class=o>::</span><span class=n>empty</span><span class=p>()</span></code></td> </tr> </tbody> </table> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>As for <a href=../../basic_json/empty/ ><code>BasicJsonType::empty()</code></a>, this does not return whether a string value is empty -- it is <code class=highlight><span class=nb>false</span></code> for any string, regardless of its length.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below uses <a href=../size/ ><code>size()</code></a> and <code>empty()</code> to decide whether a parsed message is worth acting on, without materializing it into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/end/" rel="canonical"><link href=../empty/ 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>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 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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 </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_view/end/" rel="canonical"><link href=../empty/ 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>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 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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 </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>Returns an iterator to one past the last element of an array, one past the last member value of an object, in <strong>document order</strong> -- see <a href=../begin/ ><code>begin()</code></a>. A primitive value iterates as a range of one element (itself), and a <code class=highlight><span class=kc>null</span></code> value or a <a href=../is_discarded/ >discarded</a> view iterates as an empty range (<code class=highlight><span class=n>begin</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>end</span><span class=p>()</span></code>).</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</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">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=n>iterator</span></code> is a forward iterator: unlike <code>BasicJsonType::iterator</code>, it cannot be decremented, so there is no way to reach the last element by stepping back from <code>end()</code>. Use <a href=../back/ ><code>back()</code></a> instead.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below scans a (possibly large) array of readings for the first one over a threshold, stopping the loop at <code>end()</code> as soon as one is found. Only the matching reading, if any, is ever materialized.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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<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=kt>char</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=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=n>string_t</span><span class=o>&amp;</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> <p>Finds a member with key <code>key</code> -- the first one, should the key occur more than once (see <a href=../operator%5B%5D/#notes>Notes on duplicate keys</a>). If the value is not an object, or no member has this key, <a href=../end/ ><code>end()</code></a> is returned.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</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">&para;</a></h2> <p>An iterator to the member with key <code>key</code>, or <a href=../end/ ><code>end()</code></a> if there is none or the value is not an object.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the number of members: as for <a href=../../ordered_json/ ><code>ordered_json</code></a>, members are compared one after another, in document order, stopping at the first match. Each comparison first checks the key's length -- already known from the index, without reading the key bytes -- before comparing its content. Objects with 128 or more members get a hash index of their keys while parsing, so that a lookup in them takes constant time on average.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition warning"> <p class=admonition-title>Duplicate keys: the first member wins</p> <p>If the source text repeats a key, this resolves to the <em>first</em> member with it, not to the last one that <a href=../materialize/ ><code>materialize()</code></a> and <code>parse()</code> keep. See the <a href=../operator%5B%5D/#notes>Notes on duplicate keys</a> of <code>operator[]</code> and <a href=../../../features/json_view/#duplicate-keys>Duplicate keys</a> for the reasons and for how to get the last value.</p> </div> <p>Unlike <a href=../../basic_json/find/ ><code>BasicJsonType::find</code></a>, which always returns <code class=highlight><span class=n>end</span><span class=p>()</span></code> for a non-object type, this also does so for a <a href=../is_discarded/ >discarded</a> view -- there is no separate "invalid" iterator to return.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below scans a batch of events for those that carry an optional <code>user_id</code> field, using <code>find()</code> instead of <a href=../operator%5B%5D/ ><code>operator[]</code></a> (which would throw for the events that are not objects at all) or <a href=../contains/ ><code>contains()</code></a> followed by a second lookup. Events without a match are never materialized.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
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</code></pre></div> <p>Returns the first element of an array, the first member value of an object, or the value itself if it is primitive (as for <a href=../../basic_json/front/ ><code>BasicJsonType::front()</code></a>, a primitive value is a range of one element).</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The first element or member value. For a primitive value (number, string, boolean), the value itself.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: there are no changes to the view or the document it refers to.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator214><code>invalid_iterator.214</code></a> if the view is <a href=../is_null/ >null</a> or <a href=../is_discarded/ >discarded</a>, or if it is an empty array or object.</p> <p>This exception does not carry a <a href=../../macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> path: the view has no <code>BasicJsonType</code> value to point at, so the exception is created without one, even if <code>BasicJsonType</code> was built with <code>JSON_DIAGNOSTICS</code> enabled.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Unlike <a href=../../basic_json/front/ ><code>BasicJsonType::front()</code></a>, which has undefined behavior for an empty array or object, <code>front()</code> throws <code>invalid_iterator.214</code> for an empty array, an empty object, a null value, or a discarded view.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below reads only the earliest entry of a build log with <code>front()</code>, without materializing the rest of the (possibly long) log.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
+1 -1
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<span class=n>T</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=p>;</span>
</code></pre></div> <p>Converts the value to <code>T</code>.</p> <p>For the types below, the conversion works directly on the flat index -- no <code>BasicJsonType</code> value is built for it:</p> <ul> <li><code class=highlight><span class=kt>bool</span></code></li> <li>arithmetic types other than <code class=highlight><span class=kt>bool</span></code> (for a boolean, <code class=highlight><span class=mi>0</span></code>/<code class=highlight><span class=mi>1</span></code>, exactly as for <a href=../../basic_json/get/ ><code>BasicJsonType::get&lt;T&gt;()</code></a>)</li> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>nullptr_t</span></code></li> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>basic_string</span><span class=o>&lt;</span><span class=kt>char</span><span class=p>,</span><span class=w> </span><span class=n>Traits</span><span class=p>,</span><span class=w> </span><span class=n>Alloc</span><span class=o>&gt;</span></code> (including <code>string_t</code>) -- a copy of the string</li> <li><a href=../#member-types><code>string_view_t</code></a> -- <strong>no copy</strong>: the returned view points into the document's <a href=../../basic_json_document/source/ ><code>source()</code></a> text, or, for a string that contains escape sequences, into the document's own buffer of decoded strings (see <a href=../get_string/ ><code>get_string()</code></a>)</li> <li><code>BasicJsonType</code> -- equivalent to <a href=../materialize/ ><code>materialize()</code></a></li> <li><code>basic_json_view</code> -- returns <code class=highlight><span class=o>*</span><span class=k>this</span></code></li> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>U</span><span class=p>,</span><span class=w> </span><span class=n>A</span><span class=o>&gt;</span></code> -- from an array, element by element, each converted with <code class=highlight><span class=n>get</span><span class=o>&lt;</span><span class=n>U</span><span class=o>&gt;</span><span class=p>()</span></code>; <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>basic_json_view</span><span class=o>&gt;</span></code> keeps a view of every element instead of a value</li> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o>&lt;</span><span class=n>K</span><span class=p>,</span><span class=w> </span><span class=n>V</span><span class=p>,</span><span class=w> </span><span class=n>C</span><span class=p>,</span><span class=w> </span><span class=n>A</span><span class=o>&gt;</span></code> and <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>unordered_map</span><span class=o>&lt;</span><span class=n>K</span><span class=p>,</span><span class=w> </span><span class=n>V</span><span class=p>,</span><span class=w> </span><span class=n>H</span><span class=p>,</span><span class=w> </span><span class=n>E</span><span class=p>,</span><span class=w> </span><span class=n>A</span><span class=o>&gt;</span></code>, if <code>K</code> is constructible from a <code class=highlight><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=p>)</span></code> pair -- from an object, member by member, each value converted with <code class=highlight><span class=n>get</span><span class=o>&lt;</span><span class=n>V</span><span class=o>&gt;</span><span class=p>()</span></code>; with a repeated key, the <em>last</em> value is kept, as <a href=../../basic_json/parse/ ><code>BasicJsonType::parse()</code></a> (and <a href=../materialize/ ><code>materialize()</code></a>) does; <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=p>,</span><span class=w> </span><span class=n>basic_json_view</span><span class=o>&gt;</span></code> keeps views of the members instead of values</li> </ul> <p>Every other <code>T</code> -- <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>pair</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>array</span></code>, enumerations, user types with a <code>from_json()</code>, ... -- is converted by <code class=highlight><span class=n>materialize</span><span class=p>().</span><span class=n>get</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;</span><span class=p>()</span></code>: the subtree is built into a real <code>BaLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/get_string/" rel="canonical"><link href=../get/ rel=prev><link href=../get_to/ 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_string - 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>Returns the string value as a <a href=../#member-types><code>string_view_t</code></a>, without copying it.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The string, as a <a href=../#member-types><code>string_view_t</code></a> that points either into the document's <a href=../../basic_json_document/source/ ><code>source()</code></a> text (a string with no escape sequences), or into the document's own buffer of decoded strings (a string that contains escape sequences, such as <code class=highlight><span class=s2>"\n"</span></code> or <code class=highlight><span class=s2>"\u00e9"</span></code>, which had to be decoded once when the document was parsed).</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: there are no changes to the view or the document it refers to.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>type_error.302</code></a> if the value is not a string; example: <code>"type must be string, but is array"</code>.</p> <p>This exception does not carry a <a href=../../macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> path: the view has no <code>BasicJsonType</code> value to point at, so the exception is created without one, even if <code>BasicJsonType</code> was built with <code>JSON_DIAGNOSTICS</code> enabled.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p><code>basic_json_view</code> has no <code>BasicJsonType</code> value stored anywhere, so unlike <code>BasicJsonType</code>, it has no <code>get_ref()</code> to hand out a reference to a stored <code>string_t</code>. <code>get_string()</code> (equivalently, <a href=../get/ ><code>get&lt;string_view_t&gt;()</code></a>) is the zero-copy alternative: <a href=../../basic_json/get_ref/ ><code>BasicJsonType::get_ref&lt;const string_t&amp;&gt;()</code></a> is its closest counterpart, except that it returns a view instead of a reference to a value that must already exist.</p> <p><code>get_string()</code> borrows the string: nothing is copied, whereas <a href=../get/ ><code>get&lt;std::string&gt;()</code></a> copies it. For a borrowed document, the returned <a href=../#member-types><code>string_view_t</code></a> is valid as long as the caller's buffer; for an owned one, as long as the document.</p> <p>The returned <a href=../#member-types><code>string_view_t</code></a> is valid exactly as long as the view that produced it -- see the <a href=../ >validity rules</a> of <code>basic_json_view</code> -- and, for a string with no escapes, for as long as the document's source text, which for a borrowed document must remain valid <strong>and unmodified</strong> for as long as the document exists, since floating-point values and unescaped strings are read from the source lazily.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below pulls one field out of a <abbr title="JavaScript Object Notation">JSON</abbr> text that stands in for a large <abbr title="Application Programming Interface">API</abbr> response, and shows that no <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> was allocated for it: the returned view still points inside the original buffer. A field that contains an escape sequence cannot point into the original text -- it was decoded once into the document's own buffer instead -- but still avoids a per-field allocation.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;string&gt;</span>
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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_view/get_to/" rel="canonical"><link href=../get_string/ rel=prev><link href=../is_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>get_to - 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>T</span><span class=o>&amp;</span><span class=w> </span><span class=n>get_to</span><span class=p>(</span><span class=n>T</span><span class=o>&amp;</span><span class=w> </span><span class=n>v</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
</code></pre></div> <p>Converts the value to <code>T</code> and stores it in <code>v</code>, in one of two ways:</p> <ul> <li>For the types that <a href=../get/ ><code>get&lt;T&gt;()</code></a> converts directly -- arithmetic types, <code class=highlight><span class=kt>bool</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>nullptr_t</span></code>, <a href=../#member-types><code>string_view_t</code></a>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>basic_string</span></code>, <code>BasicJsonType</code>, <code>basic_json_view</code>, <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>map</span></code>/<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>unordered_map</span></code> with string keys -- <code>v</code> is assigned: <code class=highlight><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>get</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;</span><span class=p>()</span></code>.</li> <li>For every other type, the subtree is built into a <code>BasicJsonType</code> value and <code class=highlight><span class=n>materialize</span><span class=p>().</span><span class=n>get_to</span><span class=p>(</span><span class=n>v</span><span class=p>)</span></code> is called, i.e. <code>from_json()</code> is invoked with the existing <code>v</code>, exactly as <a href=../../basic_json/get_to/ ><code>BasicJsonType::get_to()</code></a> does.</li> </ul> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>T</code></dt> <dd>the type to convert the value to</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>v</code> (out)</dt> <dd>the variable to store the converted value in</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code>v</code>, allowing calls to chain</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <ul> <li>For the directly converted types: strong exception safety. If an exception is thrown, <code>v</code> is not modified.</li> <li>For every other type: as for <a href=../../basic_json/get_to/ ><code>BasicJsonType::get_to()</code></a>. <code>materialize()</code> throws before <code>v</code> is touched, but a <code>from_json()</code> that throws may leave <code>v</code> partly modified.</li> </ul> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <ul> <li>For the directly converted types: whatever <a href=../get/ ><code>get&lt;T&gt;()</code></a> throws for the same value and <code>T</code>.</li> <li>For every other type: whatever <a href=../materialize/ ><code>materialize()</code></a> and <a href=../../basic_json/get_to/ ><code>BasicJsonType::get_to()</code></a> throw.</li> </ul> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <ul> <li>For the directly converted types: whatever <a href=../get/ ><code>get&lt;T&gt;()</code></a> has for the same <code>T</code>.</li> <li>For every other type: that of <a href=../materialize/ ><code>materialize()</code></a>, plus that of <a href=../../basic_json/get_to/ ><code>BasicJsonType::get_to()</code></a>.</li> </ul> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>The difference between the two ways matters for a <code>from_json()</code> that sets only the fields present in the <abbr title="JavaScript Object Notation">JSON</abbr>: since it runs on the existing <code>v</code>, the other fields of <code>v</code> keep their values, whereas assigning <code>get&lt;T&gt;()</code> would replace them with those of a default-constructed <code>T</code>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below reads several fields of a service configuration directly into existing variables, then uses the returned reference to fold the <code class=highlight><span class=n>host</span></code>/<code class=highlight><span class=n>port</span></code> pair into a single string in the same expression.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
+1 -1
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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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<span class=k>class</span><span class=w> </span><span class=nc>basic_json_view</span><span class=p>;</span>
</code></pre></div> <p>A read-only handle to one value of a <a href=../basic_json_document/ ><code>basic_json_document</code></a>: two pointers (a pointer to the document and a pointer into its index), trivially copyable. A view is valid as long as</p> <ul> <li>the document is alive,</li> <li>the document has not been re-parsed with <a href=../basic_json_document/read/ ><code>read()</code></a> (or <a href=../basic_json_document/parse/ ><code>parse()</code></a> into it) or shrunk with <a href=../basic_json_document/shrink_to_fit/ ><code>shrink_to_fit()</code></a> since the view was taken, and</li> <li>if the document borrows its source text, that text is still alive and unmodified (floating-point values and unescaped strings are read from it lazily).</li> </ul> <p>Moving the document itself does not invalidate its views: the index is heap-allocated independently of the <code>basic_json_document</code> object.</p> <p><code>basic_json_view</code> provides the read-only part of the <code>BasicJsonType</code> interface:</p> <ul> <li>the type-inspection functions</li> <li>element access</li> <li>lookup</li> <li>iteration</li> <li>conversion: <a href=get/ ><code>get&lt;T&gt;()</code></a>, <a href=get_string/ ><code>get_string()</code></a>, <a href=number_token/ ><code>number_token()</code></a>, and <a href=materialize/ ><code>materialize()</code></a> to build the <code>BasicJsonType</code> value of a subtree on demand</li> <li>comparison: <a href=operator_eq/ ><code>operator==</code></a> and <a href=operator_ne/ ><code>operator!=</code></a> compare two views, or a view and a <code>BasicJsonType</code> value, without ever building a <code>BasicJsonType</code> value for a view; no ordering comparison (<code class=highlight><span class=k>operator</span><span class=o>&lt;</span></code>) is provided</li> </ul> <p><a href=operator%5B%5D/ ><code>operator[]</code></a>, <a href=at/ ><code>at</code></a>, <a href=contains/ ><code>contains</code></a>, and <a href=value/ ><code>value</code></a> also accept a <a href=../json_pointer/ ><code>json_pointer</code></a>. Unlike <code>basic_json</code>, there are no implicit conversion operators (no <code class=highlight><span class=k>operator</span><span class=w> </span><span class=n>ValueType</span><span class=p>()</span></code>), and no <code class=highlight><span class=n>get_ptr</span><span class=p>()</span></code> or <code class=highlight><span class=n>get_ref</span><span class=p>()</span></code>; see <a href=get/ ><code>get</code></a>.</p> <p><code>basic_json_view</code> itself is always read-only -- it never has a <code>set</code> or <code>push_back</code> of its own. A view of an <strong>editable</strong> document (<code class=highlight><span class=n>Editable</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=nb>true</span></code>) sees every edit made through <a href=../basic_json_document/set/ ><code>basic_json_document::set</code></a> and <a href=../basic_json_document/push_back/ ><code>basic_json_document::push_back</code></a>: once a value is changed, every view that still refers to it -- including ones taken before the change -- reads the new value. See <a href=../basic_json_document/#edits>Edits</a>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BasicJsonType</code></dt> <dd>a specialization of <a href=../basic_json/ ><code>basic_json</code></a>, matching the <a href=../basic_json_document/ ><code>basic_json_document</code></a> the view was taken from.</dd> <dt><code>Editable</code></dt> <dd>whether the view is of an editable document, matching the <a href=../basic_json_document/ ><code>basic_json_document</code></a> it was taken from (optional, <code class=highlight><span class=nb>false</span></code> by default). See <a href=../basic_json_document/#edits>Edits</a>.</dd> </dl> <h2 id=specializations>Specializations<a class=headerlink href=#specializations title="Permanent link">&para;</a></h2> <ul> <li><a href=../json_view/ ><strong>json_view</strong></a> - views of a <a href=../json_document/ ><code>json_document</code></a></li> <li><a href=../ordered_json_view/ ><strong>ordered_json_view</strong></a> - views of an <a href=../ordered_json_document/ ><code>ordered_json_document</code></a></li> <li><a href=../json_editable_view/ ><strong>json_editable_view</strong></a> - views of a <a href=../json_editable_document/ ><code>json_editable_document</code></a></li> <li><a href=../ordered_json_editable_view/ ><strong>ordered_json_editable_view</strong></a> - views of an <a href=../ordered_json_editable_document/ ><code>ordered_json_editable_document</code></a></li> </ul> <h2 id=member-types>Member types<a class=headerlink href=#member-types title="Permanent link">&para;</a></h2> <ul> <li><strong>value_t</strong> - the <abbr title="JavaScript Object Notation">JSON</abbr> type enumeration, see <a href=../basic_json/value_t/ ><code>basic_jsonLine truncated
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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is an array.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is an array, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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</code></pre></div> <p>This function always returns <code class=highlight><span class=nb>false</span></code>: a document is only ever parsed from <abbr title="JavaScript Object Notation">JSON</abbr> text, never from <abbr title="Concise Binary Object Representation">CBOR</abbr> or the other binary formats, and a <abbr title="JavaScript Object Notation">JSON</abbr> text has no binary values, so a view can never refer to one. The function exists for interface parity with <a href=../../basic_json/is_binary/ ><code>BasicJsonType::is_binary</code></a>.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>false</span></code>, always.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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> is_boolean </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>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is a boolean.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is a boolean, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/is_discarded/" rel="canonical"><link href=../is_boolean/ rel=prev><link href=../is_null/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_discarded - 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> is_discarded </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_view/is_discarded/" rel="canonical"><link href=../is_boolean/ rel=prev><link href=../is_null/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_discarded - 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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</code></pre></div> <p>Returns whether this view is invalid, i.e. does not refer to a value. This is the case for a default-constructed view (see <a href=../basic_json_view/ >(constructor)</a>), and for <a href=../../basic_json_document/root/ ><code>root()</code></a> of a document that is itself <a href=../../basic_json_document/is_discarded/ >discarded</a> -- in particular, the root of a failed <a href=../../basic_json_document/parse/ ><code>parse()</code></a> with <code>allow_exceptions</code> set to <code class=highlight><span class=nb>false</span></code>.</p> <p>A discarded view is also what <a href=../operator%5B%5D/ ><code>operator[]</code></a> returns for a missing key, an index out of range, or a <abbr title="JavaScript Object Notation">JSON</abbr> pointer that cannot be resolved, and for any access on a view that is itself discarded (so a chain such as <code class=highlight><span class=n>v</span><span class=p>[</span><span class=s>"a"</span><span class=p>][</span><span class=s>"b"</span><span class=p>]</span></code> is safe). <a href=../at/ ><code>at</code></a> throws instead.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the view or its document is discarded, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>A <code>basic_json_view</code> is not convertible to <code class=highlight><span class=kt>bool</span></code>: such a conversion would mean "refers to a value", whereas <code>basic_json</code> converts to the <code class=highlight><span class=kt>bool</span></code> it holds, so the same code would silently behave differently. Test <code class=highlight><span class=o>!</span><span class=n>v</span><span class=p>.</span><span class=n>is_discarded</span><span class=p>()</span></code> explicitly.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is <code class=highlight><span class=kc>null</span></code>.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is <code class=highlight><span class=kc>null</span></code>, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
+1 -1
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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is a number, i.e. an integer, unsigned integer, or floating-point value. It is defined as <code class=highlight><span class=n>is_number_integer</span><span class=p>()</span><span class=w> </span><span class=o>||</span><span class=w> </span><span class=n>is_number_float</span><span class=p>()</span></code>.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is a number, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
@@ -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_view/is_number_float/" rel="canonical"><link href=../is_number/ rel=prev><link href=../is_number_integer/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_number_float - 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> is_number_float </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_view/is_number_float/" rel="canonical"><link href=../is_number/ rel=prev><link href=../is_number_integer/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_number_float - 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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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is a floating-point number.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is <code class=highlight><span class=n>value_t</span><span class=o>::</span><span class=n>number_float</span></code>, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>As for <a href=../../basic_json/parse/ ><code>BasicJsonType::parse</code></a>, an integer literal that does not fit into the 64-bit integer type is classified as a floating-point number, so <code>is_number_float()</code> can be <code class=highlight><span class=nb>true</span></code> even for an integer-looking token in the source text.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
@@ -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_view/is_number_integer/" rel="canonical"><link href=../is_number_float/ rel=prev><link href=../is_number_unsigned/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_number_integer - 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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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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<!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_view/is_number_integer/" rel="canonical"><link href=../is_number_float/ rel=prev><link href=../is_number_unsigned/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_number_integer - 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> is_number_integer </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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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is an integer or unsigned integer number.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is <code class=highlight><span class=n>value_t</span><span class=o>::</span><span class=n>number_integer</span></code> or <code class=highlight><span class=n>value_t</span><span class=o>::</span><span class=n>number_unsigned</span></code>, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>As for <a href=../../basic_json/is_number_integer/ ><code>BasicJsonType::is_number_integer</code></a>, this includes unsigned integer values; use <a href=../is_number_unsigned/ ><code>is_number_unsigned</code></a> to test for those specifically.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
@@ -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_view/is_number_unsigned/" rel="canonical"><link href=../is_number_integer/ rel=prev><link href=../is_object/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_number_unsigned - 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> is_number_unsigned </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_view/is_number_unsigned/" rel="canonical"><link href=../is_number_integer/ rel=prev><link href=../is_object/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_number_unsigned - 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> is_number_unsigned </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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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is an unsigned integer number.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is <code class=highlight><span class=n>value_t</span><span class=o>::</span><span class=n>number_unsigned</span></code>, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
+1 -1
View File
@@ -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_view/is_object/" rel="canonical"><link href=../is_number_unsigned/ rel=prev><link href=../is_primitive/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_object - 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>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is an object.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is an object, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is primitive, i.e. <code class=highlight><span class=kc>null</span></code>, a boolean, a number, or a string. It is defined as <code class=highlight><span class=n>is_null</span><span class=p>()</span><span class=w> </span><span class=o>||</span><span class=w> </span><span class=n>is_string</span><span class=p>()</span><span class=w> </span><span class=o>||</span><span class=w> </span><span class=n>is_boolean</span><span class=p>()</span><span class=w> </span><span class=o>||</span><span class=w> </span><span class=n>is_number</span><span class=p>()</span></code>.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is primitive, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/is_string/" rel="canonical"><link href=../is_primitive/ rel=prev><link href=../is_structured/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_string - 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> is_string </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_view/is_string/" rel="canonical"><link href=../is_primitive/ rel=prev><link href=../is_structured/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_string - 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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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is a string.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is a string, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/is_structured/" rel="canonical"><link href=../is_string/ rel=prev><link href=../items/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_structured - 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_view/is_structured/" rel="canonical"><link href=../is_string/ rel=prev><link href=../items/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>is_structured - 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> is_structured </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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</code></pre></div> <p>This function returns <code class=highlight><span class=nb>true</span></code> if and only if the value is structured, i.e. an array or an object. It is defined as <code class=highlight><span class=n>is_array</span><span class=p>()</span><span class=w> </span><span class=o>||</span><span class=w> </span><span class=n>is_object</span><span class=p>()</span></code>.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the type is structured, <code class=highlight><span class=nb>false</span></code> otherwise.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/items/" rel="canonical"><link href=../is_structured/ rel=prev><link href=../materialize/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>items - 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_view/items/" rel="canonical"><link href=../is_structured/ rel=prev><link href=../materialize/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>items - 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>Returns a range of items -- (key, value) pairs -- for use in range-based for loops. An item's <code class=highlight><span class=n>key</span><span class=p>()</span></code> is a <code class=highlight><span class=n>string_view_t</span></code> (for an array element, its index converted to a string, as for <a href=../../basic_json/items/ ><code>BasicJsonType::items()</code></a>), and its <code class=highlight><span class=n>value</span><span class=p>()</span></code> is a <code>basic_json_view</code> of the element.</p> <p>The returned type is not part of the public <abbr title="Application Programming Interface">API</abbr> and may change between versions; use a range-based for loop (see the example), or <code class=highlight><span class=k>decltype</span><span class=p>(</span><span class=n>v</span><span class=p>.</span><span class=n>items</span><span class=p>())</span></code> if you need to name it.</p> <div class=highlight><pre><span></span><code><span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>auto</span><span class=o>&amp;</span><span class=w> </span><span class=n>item</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>v</span><span class=p>.</span><span class=n>items</span><span class=p>())</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"key: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>item</span><span class=p>.</span><span class=n>key</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", value: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>item</span><span class=p>.</span><span class=n>value</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
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</code></pre></div> <p>Builds the <code>BasicJsonType</code> value of this subtree: the value <a href=../../basic_json/parse/ ><code>BasicJsonType::parse()</code></a> would have produced for the same source text, allocated for the first time by this call.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The <code>BasicJsonType</code> value of this subtree, or a discarded <code>BasicJsonType</code> value (<code class=highlight><span class=n>BasicJsonType</span><span class=p>(</span><span class=n>value_t</span><span class=o>::</span><span class=n>discarded</span><span class=p>)</span></code>) if the view is <a href=../is_discarded/ >discarded</a>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: there are no changes to the view or the document it refers to (nothing about either is mutated by this function).</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>May throw <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>bad_alloc</span></code> (via <code>BasicJsonType</code>'s allocator) if constructing the result fails.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of the subtree.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p><code>materialize()</code> replays the subtree through the same <abbr title="Simple API for XML">SAX</abbr> builder <a href=../../basic_json/parse/ ><code>BasicJsonType::parse()</code></a> uses, so the result matches it exactly -- including, for an object, that a repeated key keeps only its last value. The replay is iterative, so it is not limited by the call stack the way a naive recursive conversion would be; the <abbr title="JavaScript Object Notation">JSON</abbr> nesting depth is limited only by available memory, as for <code>BasicJsonType::parse()</code> itself.</p> <p>Unlike parsing with <a href=../../macros/json_diagnostic_positions/ ><code>JSON_DIAGNOSTIC_POSITIONS</code></a> enabled, the values produced by <code>materialize()</code> do not carry source positions. The index has the start offset of every value, but not the end of arrays, objects, and escaped strings, which the positions also need.</p> <p>Calling <code>materialize()</code> on the same view repeatedly builds a new, independent <code>BasicJsonType</code> value each time; it never caches the result.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below skips messages that are not useful -- a discarded value, or an empty array -- using only <a href=../is_array/ ><code>is_array()</code></a> and <a href=../empty/ ><code>empty()</code></a>, and calls <code>materialize()</code> only for the messages that are actually used, so no <code>BasicJsonType</code> value (and none of its per-element allocations) is ever built for the skipped ones.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;array&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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=w> </span><span class=n>shortest</span><span class=p>,</span>
<span class=w> </span><span class=n>source</span>
<span class=p>};</span>
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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_view/number_token/" rel="canonical"><link href=../number_format/ rel=prev><link href=../operator_ltlt/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>number_token - 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> number_token </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_view/number_token/" rel="canonical"><link href=../number_format/ rel=prev><link href=../operator_ltlt/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>number_token - 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> number_token </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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</code></pre></div> <p>Returns the number exactly as it appears in the source text, without parsing or rounding it.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The number's token text, as a <a href=../#member-types><code>string_view_t</code></a> into the document's <a href=../../basic_json_document/source/ ><code>source()</code></a> text -- for example <code class=highlight><span class=s>"1.50"</span></code>, <code class=highlight><span class=s>"1E2"</span></code>, <code class=highlight><span class=s>"-0"</span></code>, or an integer literal with more digits than any number type holds (such as a 30-digit integer, which <a href=../get/ ><code>get&lt;T&gt;()</code></a> and <a href=../materialize/ ><code>materialize()</code></a> can only represent approximately, as a <code>number_float_t</code>).</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: there are no changes to the view or the document it refers to.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>type_error.302</code></a> if the value is not a number; example: <code>"type must be number, but is string"</code>.</p> <p>This exception does not carry a <a href=../../macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> path: the view has no <code>BasicJsonType</code> value to point at, so the exception is created without one, even if <code>BasicJsonType</code> was built with <code>JSON_DIAGNOSTICS</code> enabled.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p><code>BasicJsonType</code> has no counterpart to this function: once a number is parsed into <code>number_integer_t</code>, <code>number_unsigned_t</code>, or <code>number_float_t</code>, its original textual form (leading zeros aside, which are already rejected by the grammar; trailing zeros in the fraction; the case and sign of the exponent; ...) is gone. <code>number_token()</code> is useful precisely where that form must survive -- a price or an identifier that must be reproduced exactly, or a number too large for any of <code>BasicJsonType</code>'s number types to hold without loss.</p> <p>The returned <a href=../#member-types><code>string_view_t</code></a> always points into the document's <a href=../../basic_json_document/source/ ><code>source()</code></a> text -- numbers are never decoded into the document's separate string buffer -- and is valid exactly as long as that text is, see the <a href=../ >validity rules</a> of <code>basic_json_view</code>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below keeps a price and an order ID exactly as they were written in an incoming order, where converting them with <a href=../get/ ><code>get&lt;T&gt;()</code></a> would lose information: the price picks up floating-point rounding, and the order ID -- more digits than a 64-bit integer holds -- can only be approximated as a <code class=highlight><span class=kt>double</span></code> once <code class=highlight><span class=n>materialize</span><span class=p>()</span></code>d.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/operator%5B%5D/" rel="canonical"><link href=../operator_ltlt/ rel=prev><link href=../operator_eq/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>operator[] - 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>basic_json_view</span><span class=w> </span><span class=k>operator</span><span class=p>[](</span><span class=n>string_view_t</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=n>basic_json_view</span><span class=w> </span><span class=k>operator</span><span class=p>[](</span><span class=k>const</span><span class=w> </span><span class=kt>char</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=n>basic_json_view</span><span class=w> </span><span class=k>operator</span><span class=p>[](</span><span class=k>const</span><span class=w> </span><span class=n>string_t</span><span class=o>&amp;</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>
+1 -1
View File
@@ -1,4 +1,4 @@
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<span class=kt>bool</span><span class=w> </span><span class=k>operator</span><span class=o>==</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>basic_json_view</span><span class=o>&amp;</span><span class=w> </span><span class=n>lhs</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json_view</span><span class=o>&amp;</span><span class=w> </span><span class=n>rhs</span><span class=p>);</span>
<span class=c1>// (2)</span>
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</code></pre></div> <p>Not available when <a href=../../macros/json_no_io/ ><code>JSON_NO_IO</code></a> is defined.</p> <p>Serializes the given view <code>v</code> to the output stream <code>o</code>, using <a href=../dump/ ><code>dump</code></a> -- exactly as <code class=highlight><span class=k>operator</span><span class=o>&lt;&lt;</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>ostream</span><span class=o>&amp;</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json</span><span class=o>&amp;</span><span class=p>)</span></code> does for a <code>basic_json</code> value.</p> <ul> <li>The indentation of the output can be controlled with the member variable <code>width</code> of the output stream <code>o</code>. For instance, using the manipulator <code>std::setw(4)</code> on <code>o</code> sets the indentation level to <code>4</code>, and the serialization result is the same as calling <code class=highlight><span class=n>v</span><span class=p>.</span><span class=n>dump</span><span class=p>(</span><span class=mi>4</span><span class=p>)</span></code>. A <code>width</code> of <code>0</code> or less (the default) selects the most compact representation, as <code class=highlight><span class=n>v</span><span class=p>.</span><span class=n>dump</span><span class=p>(</span><span class=mi>-1</span><span class=p>)</span></code> does.</li> <li>The indentation character can be controlled with the member variable <code>fill</code> of the output stream <code>o</code>. For instance, the manipulator <code>std::setfill('\t')</code> sets indentation to use a tab character rather than the default space character.</li> <li>As for <code>basic_json</code>, <code>o</code>'s <code>width</code> is reset to <code>0</code> after this call, whether or not it was greater than <code>0</code> before.</li> </ul> <p>Numbers are always written as <code class=highlight><span class=n>v</span><span class=p>.</span><span class=n>dump</span><span class=p>()</span></code> writes them by default, i.e. as with <a href=../number_format/ ><code>number_format::shortest</code></a>; there is no way to select <code class=highlight><span class=n>number_format</span><span class=o>::</span><span class=n>source</span></code> through the stream.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>o</code> (in, out)</dt> <dd>stream to write to</dd> <dt><code>v</code> (in)</dt> <dd>view to serialize</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>the stream <code>o</code></p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>May throw <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>bad_alloc</span></code>, propagated from <a href=../dump/#exceptions><code>dump</code></a>. Unlike <code class=highlight><span class=k>operator</span><span class=o>&lt;&lt;</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>ostream</span><span class=o>&amp;</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json</span><span class=o>&amp;</span><span class=p>)</span></code>, there is no <abbr title="Unicode Transformation Format">UTF</abbr>-8 decoding step that could throw <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a>, and no <code>error_handler</code> to choose between -- see the <a href=../dump/#exceptions>Exceptions</a> of <code>dump</code>.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear, as <a href=../dump/#complexity><code>dump</code></a>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below writes one record out of a larger batch straight to a log stream -- compact for a one-line entry, and pretty-printed with <code>std::setw</code>/<code>std::setfill</code> for a readable dump -- without ever building a <code>BasicJsonType</code> value for the record, or for the rest of the batch.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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> operator!= </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=kt>bool</span><span class=w> </span><span class=k>operator</span><span class=o>!=</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>basic_json_view</span><span class=o>&amp;</span><span class=w> </span><span class=n>lhs</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json_view</span><span class=o>&amp;</span><span class=w> </span><span class=n>rhs</span><span class=p>);</span>
<span class=c1>// (2)</span>
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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_view/size/" rel="canonical"><link href=../operator_ne/ rel=prev><link href=../source_offset/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>size - 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> size </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 the number of elements, as <a href=../../basic_json/size/ ><code>BasicJsonType::size()</code></a> would for the same value.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The return value depends on the type 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>0</code></td> </tr> <tr> <td>discarded</td> <td><code>0</code></td> </tr> <tr> <td>boolean</td> <td><code>1</code></td> </tr> <tr> <td>string</td> <td><code>1</code></td> </tr> <tr> <td>number</td> <td><code>1</code></td> </tr> <tr> <td>object</td> <td>number of key/value pairs</td> </tr> <tr> <td>array</td> <td>number of elements</td> </tr> </tbody> </table> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant: for an object or array, the element count is stored in the index, not counted on demand.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>As for <a href=../../basic_json/size/ ><code>BasicJsonType::size()</code></a>, this does not return the length of a string value -- it is <code>1</code> for a string, regardless of its length.</p> <p>If the source text has an object with a duplicate key, every occurrence counts towards its <code>size()</code> -- unlike <a href=../materialize/ ><code>materialize()</code></a> (and <a href=../../basic_json/parse/ ><code>BasicJsonType::parse()</code></a>), which keeps only the last value for a repeated key. This means <code class=highlight><span class=n>v</span><span class=p>.</span><span class=n>size</span><span class=p>()</span></code> can be larger than <code class=highlight><span class=n>v</span><span class=p>.</span><span class=n>materialize</span><span class=p>().</span><span class=n>size</span><span class=p>()</span></code>. See the <a href=../operator%5B%5D/#notes>Notes on duplicate keys</a> of <code>operator[]</code> for why lookups and iteration disagree on how many members there are.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below uses <code>size()</code> and <a href=../empty/ ><code>empty()</code></a> to decide whether a parsed message is worth acting on, without materializing it into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/source_offset/" rel="canonical"><link href=../size/ rel=prev><link href=../type/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>source_offset - 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>Returns the byte offset of this value in the document's <a href=../../basic_json_document/source/ ><code>source()</code></a> text, without materializing anything.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ul> <li>For a string with no escapes, a number, <code class=highlight><span class=kc>true</span></code>/<code class=highlight><span class=kc>false</span></code>/<code class=highlight><span class=kc>null</span></code>, an array, or an object: the byte offset of the first byte of the value's token (for a string: the first byte after the opening quote) in <a href=../../basic_json_document/source/ ><code>source()</code></a>.</li> <li><code class=highlight><span class=k>static_cast</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=o>&gt;</span><span class=p>(</span><span class=mi>-1</span><span class=p>)</span></code> for a <a href=../is_discarded/ >discarded</a> view, and for a string that contains escapes -- such a string was decoded once into the document's own buffer, so there is no single byte range in <code>source()</code> left to point at.</li> </ul> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This is a raw offset, not a length: the <abbr title="Application Programming Interface">API</abbr> does not (yet) expose how many bytes the token occupies in the source text, so <code>source_offset()</code> alone is enough to report <em>where</em> a value came from (for an error message, for syntax highlighting, ...) but not to slice its exact text back out of <a href=../../basic_json_document/source/ ><code>source()</code></a> for a string, whose token length is not the same as its decoded <a href=../size/ ><code>size()</code></a>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</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>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;string&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/type/" rel="canonical"><link href=../source_offset/ rel=prev><link href=../type_name/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>type - 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_view/type/" rel="canonical"><link href=../source_offset/ rel=prev><link href=../type_name/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>type - 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_json_viewtype 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> type </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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</code></pre></div> <p>Returns the type of the value this view refers to, as a value from the <a href=../../basic_json/value_t/ ><code>value_t</code></a> enumeration -- the same enumeration <a href=../../basic_json/type/ ><code>BasicJsonType::type()</code></a> uses.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The type of the value; <code class=highlight><span class=n>value_t</span><span class=o>::</span><span class=n>discarded</span></code> for a <a href=../is_discarded/ >discarded</a> view.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Unlike <a href=../../basic_json/type/ ><code>BasicJsonType::type()</code></a>, this function can never return <code class=highlight><span class=n>value_t</span><span class=o>::</span><span class=n>binary</span></code>: a <abbr title="JavaScript Object Notation">JSON</abbr> text has no binary values, so <code>type()</code> only distinguishes the eight ordinary <abbr title="JavaScript Object Notation">JSON</abbr> value types (plus <code class=highlight><span class=n>discarded</span></code>).</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below classifies several parsed documents by the type of their root value, without materializing any of them into a <code>BasicJsonType</code> value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/type_name/" rel="canonical"><link href=../type/ rel=prev><link href=../value/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>type_name - 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_json_viewtype_name 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> type_name </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_view/type_name/" rel="canonical"><link href=../type/ rel=prev><link href=../value/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>type_name - 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_json_viewtype_name 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> type_name </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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</code></pre></div> <p>Returns the type name as string to be used in error messages -- usually to indicate that a function was called on a wrong <abbr title="JavaScript Object Notation">JSON</abbr> type. Identical to <a href=../../basic_json/type_name/ ><code>BasicJsonType::type_name()</code></a>, including the extra <code class=highlight><span class=s>"discarded"</span></code> return value for a <a href=../is_discarded/ >discarded</a> view (<code>BasicJsonType::type_name()</code> produces the same string for a discarded <code>BasicJsonType</code> value).</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>a string representation of the type (<a href=../../basic_json/value_t/ ><code>value_t</code></a>):</p> <table> <thead> <tr> <th>Value type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=kc>null</span></code></td> <td><code>"null"</code></td> </tr> <tr> <td>boolean</td> <td><code>"boolean"</code></td> </tr> <tr> <td>string</td> <td><code>"string"</code></td> </tr> <tr> <td>number (integer, unsigned integer, floating-point)</td> <td><code>"number"</code></td> </tr> <tr> <td>object</td> <td><code>"object"</code></td> </tr> <tr> <td>array</td> <td><code>"array"</code></td> </tr> <tr> <td>discarded</td> <td><code>"discarded"</code></td> </tr> </tbody> </table> <p><code>type_name()</code> never returns <code class=highlight><span class=s>"binary"</span></code>, since a <abbr title="JavaScript Object Notation">JSON</abbr> text has no binary values (see <a href=../is_binary/ ><code>is_binary()</code></a>); it also never returns <code class=highlight><span class=s>"invalid"</span></code>, since a view's <code class=highlight><span class=n>kind</span></code> always comes from a value the parser actually produced.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below reports why some parsed messages were rejected, using only <code>type_name()</code> -- no <code>BasicJsonType</code> value is ever built for the ones that are wrong, and the message text matches what <a href=../../basic_json/type_name/ ><code>BasicJsonType::type_name()</code></a> would produce for the same value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
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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_view/value/" rel="canonical"><link href=../type_name/ rel=prev><link href=../../byte_container_with_subtype/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>value - 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>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=o>&gt;</span>
<span class=n>T</span><span class=w> </span><span class=n>value</span><span class=p>(</span><span class=n>string_view_t</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=w> </span><span class=n>T</span><span class=o>&amp;</span><span class=w> </span><span class=n>default_value</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
<span class=n>string_t</span><span class=w> </span><span class=nf>value</span><span class=p>(</span><span class=n>string_view_t</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=w> </span><span class=kt>char</span><span class=o>*</span><span class=w> </span><span class=n>default_value</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>