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@@ -351,9 +351,8 @@ The number types can be changed with template parameters.
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A `basic_json` type that uses `#!c long double` as floating-point type.
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```cpp hl_lines="2"
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using json_ld = nlohmann::basic_json<std::map, std::vector, std::string, bool,
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std::int64_t, std::uint64_t, long double>;
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```cpp hl_lines="1"
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using json_ld = nlohmann::json::with_float_t<long double>;
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```
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Note values should then be parsed with `json_ld::parse` rather than `json::parse` as the latter would parse
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@@ -59,6 +59,5 @@ val=nan
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<span class=w> </span><span class=c1>// otherwise, take appropriate action</span>
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<span class=w> </span><span class=c1>// ...</span>
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<span class=p>}</span>
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</code></pre></div> <p>Note this approach also has the advantage that it can react on non-numerical <abbr title="JavaScript Object Notation">JSON</abbr> value types such as strings.</p> <p>(Example taken from <a href="https://github.com/nlohmann/json/issues/777#issuecomment-459968458">#777</a>.)</p> </div> <h3 id=determine-number-types>Determine number types<a class=headerlink href=#determine-number-types title="Permanent link">¶</a></h3> <p>As the example in <a href=#number-conversion>Number conversion</a> shows, there are different functions to determine the type of the stored number:</p> <ul> <li><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a> returns <code class=highlight><span class=nb>true</span></code> for any number type</li> <li><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a> returns <code class=highlight><span class=nb>true</span></code> for signed and unsigned integers</li> <li><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a> returns <code class=highlight><span class=nb>true</span></code> for unsigned integers only</li> <li><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a> returns <code class=highlight><span class=nb>true</span></code> for floating-point numbers</li> <li><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a> returns <code class=highlight><span class=s>"number"</span></code> for any number type</li> <li><a href=../../../api/basic_json/type/ ><code>type()</code></a> returns a different enumerator of <a href=../../../api/basic_json/value_t/ ><code>value_t</code></a> for all number types</li> </ul> <table> <thead> <tr> <th>function</th> <th>unsigned integer</th> <th>signed integer</th> <th>floating-point</th> <th>string</th> </tr> </thead> <tbody> <tr> <td><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"string"</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type/ ><code>type()</code></a></td> <td><code>number_unsigned</code></td> <td><code>number_integer</code></td> <td><code>number_float</code></td> <td><code>string</code></td> </tr> </tbody> </table> <h3 id=template-number-types>Template number types<a class=headerlink href=#template-number-types title="Permanent link">¶</a></h3> <p>The number types can be changed with template parameters.</p> <table> <thead> <tr> <th>position</th> <th>number type</th> <th>default type</th> <th>possible values</th> </tr> </thead> <tbody> <tr> <td>5</td> <td>signed integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int16_t</span></code>, etc.</td> </tr> <tr> <td>6</td> <td>unsigned integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</spanLine truncated
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<span class=hll><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span><span class=p>,</span><span class=w> </span><span class=kt>long</span><span class=w> </span><span class=kt>double</span><span class=o>></span><span class=p>;</span>
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</span></code></pre></div> <p>Note values should then be parsed with <code>json_ld::parse</code> rather than <code>json::parse</code> as the latter would parse floating-point values to <code class=highlight><span class=kt>double</span></code> before then converting them to <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 2, 2026 09:32:15 UTC">October 2, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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</code></pre></div> <p>Note this approach also has the advantage that it can react on non-numerical <abbr title="JavaScript Object Notation">JSON</abbr> value types such as strings.</p> <p>(Example taken from <a href="https://github.com/nlohmann/json/issues/777#issuecomment-459968458">#777</a>.)</p> </div> <h3 id=determine-number-types>Determine number types<a class=headerlink href=#determine-number-types title="Permanent link">¶</a></h3> <p>As the example in <a href=#number-conversion>Number conversion</a> shows, there are different functions to determine the type of the stored number:</p> <ul> <li><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a> returns <code class=highlight><span class=nb>true</span></code> for any number type</li> <li><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a> returns <code class=highlight><span class=nb>true</span></code> for signed and unsigned integers</li> <li><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a> returns <code class=highlight><span class=nb>true</span></code> for unsigned integers only</li> <li><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a> returns <code class=highlight><span class=nb>true</span></code> for floating-point numbers</li> <li><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a> returns <code class=highlight><span class=s>"number"</span></code> for any number type</li> <li><a href=../../../api/basic_json/type/ ><code>type()</code></a> returns a different enumerator of <a href=../../../api/basic_json/value_t/ ><code>value_t</code></a> for all number types</li> </ul> <table> <thead> <tr> <th>function</th> <th>unsigned integer</th> <th>signed integer</th> <th>floating-point</th> <th>string</th> </tr> </thead> <tbody> <tr> <td><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"string"</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type/ ><code>type()</code></a></td> <td><code>number_unsigned</code></td> <td><code>number_integer</code></td> <td><code>number_float</code></td> <td><code>string</code></td> </tr> </tbody> </table> <h3 id=template-number-types>Template number types<a class=headerlink href=#template-number-types title="Permanent link">¶</a></h3> <p>The number types can be changed with template parameters.</p> <table> <thead> <tr> <th>position</th> <th>number type</th> <th>default type</th> <th>possible values</th> </tr> </thead> <tbody> <tr> <td>5</td> <td>signed integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int16_t</span></code>, etc.</td> </tr> <tr> <td>6</td> <td>unsigned integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</spanLine truncated
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||||
</span></code></pre></div> <p>Note values should then be parsed with <code>json_ld::parse</code> rather than <code>json::parse</code> as the latter would parse floating-point values to <code class=highlight><span class=kt>double</span></code> before then converting them to <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 8, 2026 14:11:16 UTC">October 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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|
||||
@@ -288,8 +288,7 @@ Example
|
||||
A `basic_json` type that uses `long double` as floating-point type.
|
||||
|
||||
```
|
||||
using json_ld = nlohmann::basic_json<std::map, std::vector, std::string, bool,
|
||||
std::int64_t, std::uint64_t, long double>;
|
||||
using json_ld = nlohmann::json::with_float_t<long double>;
|
||||
```
|
||||
|
||||
Note values should then be parsed with `json_ld::parse` rather than `json::parse` as the latter would parse floating-point values to `double` before then converting them to `long double`.
|
||||
@@ -8,6 +8,10 @@ these requirements so they do not have to be discovered by trial and error. Each
|
||||
that are known to work for that parameter and the ones that do not, checked against Boost 1.83, Abseil 20250127.0,
|
||||
Folly, EASTL 3.21, `ankerl::unordered_dense`, `phmap`, `gtl`, `robin_hood`, `tsl::ordered_map`, and Qt 6.
|
||||
|
||||
To change a single template parameter and keep the others, use the member alias templates
|
||||
[`with_*_t`](../../api/basic_json/with_t.md); for instance, `nlohmann::json::with_float_t<long double>` is `json` with
|
||||
`#!cpp long double` as [`number_float_t`](../../api/basic_json/number_float_t.md).
|
||||
|
||||
## How to read this page
|
||||
|
||||
Requirements are split into two groups:
|
||||
@@ -143,7 +147,7 @@ struct unordered_map_object
|
||||
using base_t::base_t;
|
||||
};
|
||||
|
||||
using unordered_json = nlohmann::basic_json<unordered_map_object>;
|
||||
using unordered_json = nlohmann::json::with_object_t<unordered_map_object>;
|
||||
```
|
||||
|
||||
Whether `#!cpp std::unordered_map` can be instantiated at all depends on the standard library: `object_t` is formed
|
||||
@@ -176,7 +180,7 @@ struct flat_hash_object
|
||||
using base_t::base_t;
|
||||
};
|
||||
|
||||
using flat_hash_json = nlohmann::basic_json<flat_hash_object>;
|
||||
using flat_hash_json = nlohmann::json::with_object_t<flat_hash_object>;
|
||||
```
|
||||
|
||||
`absl::node_hash_map` keeps references to the mapped values valid across insertions; `absl::flat_hash_map` does not,
|
||||
|
||||
@@ -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/features/types/template_parameters/" rel="canonical"><link href=../number_handling/ rel=prev><link href=../../../integration/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Template Parameter Requirements - 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> Template Parameter Requirements </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 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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 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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/features/types/template_parameters/" rel="canonical"><link href=../number_handling/ rel=prev><link href=../../../integration/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Template Parameter Requirements - 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> Template Parameter Requirements </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 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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 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|
||||
<span class=w> </span><span class=n>basic_json</span><span class=p>,</span><span class=w> </span><span class=c1>// mapped_type</span>
|
||||
<span class=w> </span><span class=n>default_object_comparator_t</span><span class=p>,</span><span class=w> </span><span class=c1>// key_compare</span>
|
||||
<span class=w> </span><span class=n>AllocatorType</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=n>pair</span><span class=o><</span><span class=k>const</span><span class=w> </span><span class=n>StringType</span><span class=p>,</span>
|
||||
@@ -11,7 +11,7 @@
|
||||
<span class=w> </span><span class=k>using</span><span class=w> </span><span class=n>base_t</span><span class=o>::</span><span class=n>base_t</span><span class=p>;</span>
|
||||
<span class=p>};</span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>unordered_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>basic_json</span><span class=o><</span><span class=n>unordered_map_object</span><span class=o>></span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=n>unordered_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=o>::</span><span class=n>with_object_t</span><span class=o><</span><span class=n>unordered_map_object</span><span class=o>></span><span class=p>;</span>
|
||||
</code></pre></div> <p>Whether <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>unordered_map</span></code> can be instantiated at all depends on the standard library: <code>object_t</code> is formed while <code>basic_json</code> is still incomplete (see the warning above), and libstdc++ 9 needs the size of the mapped type to instantiate the hash map's node type, so the adapter does not compile there. Newer libstdc++ versions, and the hash maps listed below, do not have that problem.</p> <p>The adapter above works verbatim for Abseil's, Boost's, <code>phmap</code>'s and <code>gtl</code>'s hash maps, which all place the hash function third and take a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>pair</span><span class=o><</span><span class=k>const</span><span class=w> </span><span class=n>Key</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=o>></span></code> allocator fifth. Two need a different adapter:</p> <ul> <li><code>ankerl::unordered_dense</code> expects an allocator over <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>pair</span><span class=o><</span><span class=n>Key</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=o>></span></code> (non-const key), so the allocator has to be rebound to that or dropped.</li> <li><code>robin_hood</code>'s fifth parameter is the non-type <code>MaxLoadFactor100</code>, so its adapter must drop the allocator entirely.</li> </ul> <p>None of these hash maps defines <code>key_compare</code>, so all of them additionally rely on <code>object_comparator_t</code> falling back to <a href=../../../api/basic_json/default_object_comparator_t/ ><code>default_object_comparator_t</code></a>; see <a href=../../../api/basic_json/object_comparator_t/ ><code>object_comparator_t</code></a>.</p> <h4 id=abseil-hash-maps>Abseil hash maps<a class=headerlink href=#abseil-hash-maps title="Permanent link">¶</a></h4> <p><code>absl::flat_hash_map</code> and <code>absl::node_hash_map</code> tolerate an incomplete value type, but they take a hash function as their third template argument. The same adapter as for <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>unordered_map</span></code> makes them usable:</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o><</span><span class=k>class</span><span class=w> </span><span class=nc>Key</span><span class=p>,</span><span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>T</span><span class=p>,</span><span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>IgnoredCompare</span><span class=p>,</span><span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>Allocator</span><span class=o>></span>
|
||||
<span class=k>struct</span><span class=w> </span><span class=nc>flat_hash_object</span>
|
||||
<span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>absl</span><span class=o>::</span><span class=n>flat_hash_map</span><span class=o><</span><span class=n>Key</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=p>,</span><span class=w> </span><span class=n>absl</span><span class=o>::</span><span class=n>Hash</span><span class=o><</span><span class=n>Key</span><span class=o>></span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>equal_to</span><span class=o><</span><span class=n>Key</span><span class=o>></span><span class=p>,</span><span class=w> </span><span class=n>Allocator</span><span class=o>></span>
|
||||
@@ -20,7 +20,7 @@
|
||||
<span class=w> </span><span class=k>using</span><span class=w> </span><span class=n>base_t</span><span class=o>::</span><span class=n>base_t</span><span class=p>;</span>
|
||||
<span class=p>};</span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>flat_hash_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>basic_json</span><span class=o><</span><span class=n>flat_hash_object</span><span class=o>></span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=n>flat_hash_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=o>::</span><span class=n>with_object_t</span><span class=o><</span><span class=n>flat_hash_object</span><span class=o>></span><span class=p>;</span>
|
||||
</code></pre></div> <p><code>absl::node_hash_map</code> keeps references to the mapped values valid across insertions; <code>absl::flat_hash_map</code> does not, which makes it behave like <a href=../../../api/ordered_json/ ><code>ordered_json</code></a> with respect to <a href=../../../api/basic_json/#iterator-invalidation>iterator invalidation</a>. Both expose a <code>capacity()</code> member function, so <a href=../../../api/macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> treats them conservatively and keeps the parent pointers correct either way.</p> <h4 id=iteration-order>Iteration order<a class=headerlink href=#iteration-order title="Permanent link">¶</a></h4> <p>The library never relies on the container's iteration order for correctness; it does determine the order in which object keys are serialized by <a href=../../../api/basic_json/dump/ ><code>dump</code></a> and visited by <a href=../../../api/basic_json/items/ ><code>items</code></a>. See <a href=../../object_order/ >Object Order</a>.</p> <h4 id=capacity-marks-a-container-as-insertion-ordered><code>capacity()</code> marks a container as insertion-ordered<a class=headerlink href=#capacity-marks-a-container-as-insertion-ordered title="Permanent link">¶</a></h4> <p>With <a href=../../../api/macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> enabled, the library detects insertion-ordered maps by probing for a <code>capacity()</code> member function (<code>nlohmann::ordered_map</code> inherits it from <code>std::vector</code>) and refreshes all parent pointers after every insertion. An <code>ObjectType</code> that happens to have a <code>capacity()</code> member is therefore treated conservatively -- this is correct, but slower.</p> <h4 id=key-order-and-duplicate-keys>Key order and duplicate keys<a class=headerlink href=#key-order-and-duplicate-keys title="Permanent link">¶</a></h4> <p>The library does not sort or de-duplicate keys itself; the behavior described in <a href=../../../api/basic_json/object_t/ ><code>object_t</code></a> is entirely the behavior of the chosen container.</p> <div class="admonition tip"> <p class=admonition-title>Reference implementation</p> <p><code>docs/mkdocs/docs/examples/custom_object_type.hpp</code> wraps a private <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span></code> and satisfies every requirement above. It does not define <code>key_compare</code>, so <code>object_comparator_t</code> falls back to <a href=../../../api/basic_json/default_object_comparator_t/ ><code>default_object_comparator_t</code></a> -- a good starting point for a custom <code>ObjectType</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#pragma once</span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><map></span>
|
||||
@@ -167,13 +167,12 @@
|
||||
<span class=p>};</span>
|
||||
</code></pre></div> </div> <details class=example> <summary>Example: use the custom <code>ObjectType</code></summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><type_traits></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><vector></span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf>"custom_object_type.hpp"</span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>custom_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>basic_json</span><span class=o><</span><span class=n>custom_object_type</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>></span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=n>custom_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=o>::</span><span class=n>with_object_t</span><span class=o><</span><span class=n>custom_object_type</span><span class=o>></span><span class=p>;</span>
|
||||
|
||||
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
|
||||
<span class=p>{</span>
|
||||
@@ -356,13 +355,12 @@
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=p>};</span>
|
||||
</code></pre></div> </div> <details class=example> <summary>Example: use the custom <code>ArrayType</code></summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><map></span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf>"custom_array_type.hpp"</span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>custom_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>basic_json</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=p>,</span><span class=w> </span><span class=n>custom_array_type</span><span class=o>></span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=n>custom_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=o>::</span><span class=n>with_array_t</span><span class=o><</span><span class=n>custom_array_type</span><span class=o>></span><span class=p>;</span>
|
||||
|
||||
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
|
||||
<span class=p>{</span>
|
||||
@@ -523,14 +521,12 @@
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=p>};</span>
|
||||
</code></pre></div> </div> <details class=example> <summary>Example: use the custom <code>StringType</code></summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><map></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><vector></span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf>"custom_string_type.hpp"</span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>custom_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>basic_json</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=p>,</span><span class=w> </span><span class=n>custom_string_type</span><span class=o>></span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=n>custom_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=o>::</span><span class=n>with_string_t</span><span class=o><</span><span class=n>custom_string_type</span><span class=o>></span><span class=p>;</span>
|
||||
|
||||
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
|
||||
<span class=p>{</span>
|
||||
@@ -665,19 +661,13 @@
|
||||
<span class=w> </span><span class=k>return</span><span class=w> </span><span class=n>lhs</span><span class=p>.</span><span class=n>data_</span><span class=w> </span><span class=o><</span><span class=w> </span><span class=n>rhs</span><span class=p>.</span><span class=n>data_</span><span class=p>;</span>
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=p>};</span>
|
||||
</code></pre></div> </div> <details class=example> <summary>Example: use the custom <code>BinaryType</code></summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><cstdint></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><map></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><string></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><vector></span>
|
||||
</code></pre></div> </div> <details class=example> <summary>Example: use the custom <code>BinaryType</code></summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf>"custom_binary_type.hpp"</span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>custom_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>basic_json</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=p>,</span><span class=w> </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=kt>bool</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span><span class=p>,</span><span class=w> </span><span class=kt>double</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>allocator</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>adl_serializer</span><span class=p>,</span><span class=w> </span><span class=n>custom_binary_type</span><span class=o>></span><span class=p>;</span>
|
||||
<span class=k>using</span><span class=w> </span><span class=n>custom_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=o>::</span><span class=n>with_binary_t</span><span class=o><</span><span class=n>custom_binary_type</span><span class=o>></span><span class=p>;</span>
|
||||
|
||||
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
|
||||
<span class=p>{</span>
|
||||
@@ -688,4 +678,4 @@
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>1</span><span class=p>,</span><span class=mi>2</span><span class=p>,</span><span class=mi>3</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=kc>null</span><span class=p>}</span>
|
||||
<span class=kc>true</span>
|
||||
</code></pre></div> </details> <h3 id=compatible-containers_2>Compatible containers<a class=headerlink href=#compatible-containers_2 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Container</th> <th>Notes</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code> (default)</td> <td></td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=kt>char</span><span class=o>></span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>></span></code></td> <td><code>dump()</code> writes the bytes as 0..255 whichever is used</td> </tr> <tr> <td><code>boost::container::vector<std::uint8_t></code>, <code>boost::container::small_vector<std::uint8_t, N></code></td> <td></td> </tr> <tr> <td><code>absl::InlinedVector<std::uint8_t, N></code></td> <td>usable here, unlike as an <code>ArrayType</code>, because the value type is complete</td> </tr> <tr> <td><code>eastl::vector<std::uint8_t></code></td> <td>usable here, unlike as an <code>ArrayType</code>, because <code>max_size()</code> is not needed</td> </tr> <tr> <td><code>folly::fbvector<std::uint8_t></code></td> <td>requires C++20, see the note above</td> </tr> </tbody> </table> <h3 id=containers-that-cannot-be-used_2>Containers that cannot be used<a class=headerlink href=#containers-that-cannot-be-used_2 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Container</th> <th>Reason</th> </tr> </thead> <tbody> <tr> <td><code>QByteArray</code></td> <td>no <code>empty()</code> (it spells that <code>isEmpty()</code>); its <code>insert</code> takes an index rather than an iterator; and it converts to <code>string_t</code>, which makes <code>to_json</code> ambiguous between a string and a binary value</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code></td> <td><code>binary_t::container_type</code> and <code>string_t</code> would be the same type, so the two <a href=../../../api/basic_json/swap/ ><code>swap</code></a> overloads collide and <code>basic_json</code> cannot be instantiated at all</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code></td> <td>storage is not contiguous, so there is no <code>data()</code></td> </tr> <tr> <td>containers whose <code>value_type</code> is wider than one byte</td> <td>see above -- accepted by the compiler, wrong at runtime</td> </tr> </tbody> </table> <h2 id=custombaseclass><code>CustomBaseClass</code><a class=headerlink href=#custombaseclass title="Permanent link">¶</a></h2> <p><code>CustomBaseClass</code> is an extension point: unless it is <code class=highlight><span class=kt>void</span></code> (the default, which selects the empty <code>nlohmann::json_default_base</code>), <code>basic_json</code> publicly derives from it.</p> <h3 id=always-required_9>Always required<a class=headerlink href=#always-required_9 title="Permanent link">¶</a></h3> <ul> <li>A non-<code>final</code>, default-constructible class type.</li> <li><code>basic_json</code> is copy-/move-constructible and copy-/move-assignable only if <code>CustomBaseClass</code> is.</li> </ul> <h3 id=notes_2>Notes<a class=headerlink href=#notes_2 title="Permanent link">¶</a></h3> <p><code>basic_json</code> is documented to be a <a href="https://en.cppreference.com/w/cpp/named_req/StandardLayoutType">StandardLayoutType</a>. Because <code>basic_json</code> has non-static data members of its own, a <code>CustomBaseClass</code> with non-static data members forfeits this guarantee.</p> <p>Note the namespace of <code>CustomBaseClass</code> becomes an associated namespace of <code>basic_json</code> for the purpose of argument-dependent lookup.</p> <p>See <a href=../../../api/basic_json/json_base_class_t/ ><code>json_base_class_t</code></a> for an example.</p> <h3 id=compatible-types_6>Compatible types<a class=headerlink href=#compatible-types_6 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Type</th> <th>Support</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=kt>void</span></code> (default)</td> <td>an empty base class is used; no effect on <code>basic_json</code></td> </tr> <tr> <td>any default-constructible, non-<code>final</code> class</td> <td>full; see <a href=../../../api/basic_json/json_base_class_t/ ><code>json_base_class_t</code></a></td> </tr>Line truncated
|
||||
</code></pre></div> </details> <h3 id=compatible-containers_2>Compatible containers<a class=headerlink href=#compatible-containers_2 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Container</th> <th>Notes</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code> (default)</td> <td></td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=kt>char</span><span class=o>></span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>></span></code></td> <td><code>dump()</code> writes the bytes as 0..255 whichever is used</td> </tr> <tr> <td><code>boost::container::vector<std::uint8_t></code>, <code>boost::container::small_vector<std::uint8_t, N></code></td> <td></td> </tr> <tr> <td><code>absl::InlinedVector<std::uint8_t, N></code></td> <td>usable here, unlike as an <code>ArrayType</code>, because the value type is complete</td> </tr> <tr> <td><code>eastl::vector<std::uint8_t></code></td> <td>usable here, unlike as an <code>ArrayType</code>, because <code>max_size()</code> is not needed</td> </tr> <tr> <td><code>folly::fbvector<std::uint8_t></code></td> <td>requires C++20, see the note above</td> </tr> </tbody> </table> <h3 id=containers-that-cannot-be-used_2>Containers that cannot be used<a class=headerlink href=#containers-that-cannot-be-used_2 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Container</th> <th>Reason</th> </tr> </thead> <tbody> <tr> <td><code>QByteArray</code></td> <td>no <code>empty()</code> (it spells that <code>isEmpty()</code>); its <code>insert</code> takes an index rather than an iterator; and it converts to <code>string_t</code>, which makes <code>to_json</code> ambiguous between a string and a binary value</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code></td> <td><code>binary_t::container_type</code> and <code>string_t</code> would be the same type, so the two <a href=../../../api/basic_json/swap/ ><code>swap</code></a> overloads collide and <code>basic_json</code> cannot be instantiated at all</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code></td> <td>storage is not contiguous, so there is no <code>data()</code></td> </tr> <tr> <td>containers whose <code>value_type</code> is wider than one byte</td> <td>see above -- accepted by the compiler, wrong at runtime</td> </tr> </tbody> </table> <h2 id=custombaseclass><code>CustomBaseClass</code><a class=headerlink href=#custombaseclass title="Permanent link">¶</a></h2> <p><code>CustomBaseClass</code> is an extension point: unless it is <code class=highlight><span class=kt>void</span></code> (the default, which selects the empty <code>nlohmann::json_default_base</code>), <code>basic_json</code> publicly derives from it.</p> <h3 id=always-required_9>Always required<a class=headerlink href=#always-required_9 title="Permanent link">¶</a></h3> <ul> <li>A non-<code>final</code>, default-constructible class type.</li> <li><code>basic_json</code> is copy-/move-constructible and copy-/move-assignable only if <code>CustomBaseClass</code> is.</li> </ul> <h3 id=notes_2>Notes<a class=headerlink href=#notes_2 title="Permanent link">¶</a></h3> <p><code>basic_json</code> is documented to be a <a href="https://en.cppreference.com/w/cpp/named_req/StandardLayoutType">StandardLayoutType</a>. Because <code>basic_json</code> has non-static data members of its own, a <code>CustomBaseClass</code> with non-static data members forfeits this guarantee.</p> <p>Note the namespace of <code>CustomBaseClass</code> becomes an associated namespace of <code>basic_json</code> for the purpose of argument-dependent lookup.</p> <p>See <a href=../../../api/basic_json/json_base_class_t/ ><code>json_base_class_t</code></a> for an example.</p> <h3 id=compatible-types_6>Compatible types<a class=headerlink href=#compatible-types_6 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Type</th> <th>Support</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=kt>void</span></code> (default)</td> <td>an empty base class is used; no effect on <code>basic_json</code></td> </tr> <tr> <td>any default-constructible, non-<code>final</code> class</td> <td>full; see <a href=../../../api/basic_json/json_base_class_t/ ><code>json_base_class_t</code></a></td> </tr>Line truncated
|
||||
@@ -2,6 +2,8 @@
|
||||
|
||||
Class [`basic_json`](https://json.nlohmann.me/api/basic_json/index.md) is configurable through eleven template parameters. The library never formally states what a type passed for one of these parameters has to provide -- the requirements are implied by the way the library uses the resulting [`object_t`](https://json.nlohmann.me/api/basic_json/object_t/index.md), [`array_t`](https://json.nlohmann.me/api/basic_json/array_t/index.md), [`string_t`](https://json.nlohmann.me/api/basic_json/string_t/index.md), etc. This page collects these requirements so they do not have to be discovered by trial and error. Each section lists the concrete types that are known to work for that parameter and the ones that do not, checked against Boost 1.83, Abseil 20250127.0, Folly, EASTL 3.21, `ankerl::unordered_dense`, `phmap`, `gtl`, `robin_hood`, `tsl::ordered_map`, and Qt 6.
|
||||
|
||||
To change a single template parameter and keep the others, use the member alias templates [`with_*_t`](https://json.nlohmann.me/api/basic_json/with_t/index.md); for instance, `nlohmann::json::with_float_t<long double>` is `json` with `long double` as [`number_float_t`](https://json.nlohmann.me/api/basic_json/number_float_t/index.md).
|
||||
|
||||
## How to read this page
|
||||
|
||||
Requirements are split into two groups:
|
||||
@@ -94,7 +96,7 @@ struct unordered_map_object
|
||||
using base_t::base_t;
|
||||
};
|
||||
|
||||
using unordered_json = nlohmann::basic_json<unordered_map_object>;
|
||||
using unordered_json = nlohmann::json::with_object_t<unordered_map_object>;
|
||||
```
|
||||
|
||||
Whether `std::unordered_map` can be instantiated at all depends on the standard library: `object_t` is formed while `basic_json` is still incomplete (see the warning above), and libstdc++ 9 needs the size of the mapped type to instantiate the hash map's node type, so the adapter does not compile there. Newer libstdc++ versions, and the hash maps listed below, do not have that problem.
|
||||
@@ -119,7 +121,7 @@ struct flat_hash_object
|
||||
using base_t::base_t;
|
||||
};
|
||||
|
||||
using flat_hash_json = nlohmann::basic_json<flat_hash_object>;
|
||||
using flat_hash_json = nlohmann::json::with_object_t<flat_hash_object>;
|
||||
```
|
||||
|
||||
`absl::node_hash_map` keeps references to the mapped values valid across insertions; `absl::flat_hash_map` does not, which makes it behave like [`ordered_json`](https://json.nlohmann.me/api/ordered_json/index.md) with respect to [iterator invalidation](https://json.nlohmann.me/api/basic_json/#iterator-invalidation). Both expose a `capacity()` member function, so [`JSON_DIAGNOSTICS`](https://json.nlohmann.me/api/macros/json_diagnostics/index.md) treats them conservatively and keeps the parent pointers correct either way.
|
||||
@@ -292,13 +294,12 @@ Example: use the custom `ObjectType`
|
||||
```
|
||||
#include <iostream>
|
||||
#include <type_traits>
|
||||
#include <vector>
|
||||
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
#include "custom_object_type.hpp"
|
||||
|
||||
using custom_json = nlohmann::basic_json<custom_object_type, std::vector>;
|
||||
using custom_json = nlohmann::json::with_object_t<custom_object_type>;
|
||||
|
||||
int main()
|
||||
{
|
||||
@@ -553,13 +554,12 @@ Example: use the custom `ArrayType`
|
||||
|
||||
```
|
||||
#include <iostream>
|
||||
#include <map>
|
||||
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
#include "custom_array_type.hpp"
|
||||
|
||||
using custom_json = nlohmann::basic_json<std::map, custom_array_type>;
|
||||
using custom_json = nlohmann::json::with_array_t<custom_array_type>;
|
||||
|
||||
int main()
|
||||
{
|
||||
@@ -828,14 +828,12 @@ Example: use the custom `StringType`
|
||||
|
||||
```
|
||||
#include <iostream>
|
||||
#include <map>
|
||||
#include <vector>
|
||||
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
#include "custom_string_type.hpp"
|
||||
|
||||
using custom_json = nlohmann::basic_json<std::map, std::vector, custom_string_type>;
|
||||
using custom_json = nlohmann::json::with_string_t<custom_string_type>;
|
||||
|
||||
int main()
|
||||
{
|
||||
@@ -1128,19 +1126,13 @@ class custom_binary_type
|
||||
Example: use the custom `BinaryType`
|
||||
|
||||
```
|
||||
#include <cstdint>
|
||||
#include <iostream>
|
||||
#include <map>
|
||||
#include <string>
|
||||
#include <vector>
|
||||
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
#include "custom_binary_type.hpp"
|
||||
|
||||
using custom_json = nlohmann::basic_json<std::map, std::vector, std::string, bool,
|
||||
std::int64_t, std::uint64_t, double, std::allocator,
|
||||
nlohmann::adl_serializer, custom_binary_type>;
|
||||
using custom_json = nlohmann::json::with_binary_t<custom_binary_type>;
|
||||
|
||||
int main()
|
||||
{
|
||||
|
||||
Reference in new issue
Block a user