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@@ -85,7 +85,7 @@ The class satisfies the following concept requirements:
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- [EqualityComparable](https://en.cppreference.com/w/cpp/named_req/EqualityComparable): JSON values can be compared with
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`==`, see [`operator==`](operator_eq.md).
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- [LessThanComparable](https://en.cppreference.com/w/cpp/named_req/LessThanComparable): JSON values can be compared with
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`<`, see [`operator<`](operator_le.md).
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`<`, see [`operator<`](operator_lt.md).
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- [Swappable](https://en.cppreference.com/w/cpp/named_req/Swappable): Any JSON lvalue or rvalue of can be swapped with
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any lvalue or rvalue of other compatible types, using unqualified function `swap`.
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- [NullablePointer](https://en.cppreference.com/w/cpp/named_req/NullablePointer): JSON values can be compared against
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@@ -27,7 +27,7 @@ To store objects in C++, a type is defined by the template parameters explained
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### Default type
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With the default values for `ArrayType` (`std::vector`) and `AllocatorType` (`std::allocator`), the default value for
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With the default values for `ArrayType` (`std::vector`) and `AllocatorType` (`std::allocator`), the default type for
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`array_t` is:
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```cpp
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@@ -1,5 +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/array_t/" rel="canonical"><link href=../array/ rel=prev><link href=../as_base_class/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> array_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> arrays.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> arrays as follows:</p> <blockquote> <p>An array is an ordered sequence of zero or more values.</p> </blockquote> <p>To store objects in C++, a type is defined by the template parameters explained below.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ArrayType</code></dt> <dd>container type to store arrays. It must be a vector-like container: the library uses <code>operator[]</code>, <code>at()</code>, and <code>resize()</code>, and requires random-access iterators. <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span></code> and <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> qualify; <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span></code> does not. See <a href=../../../features/types/template_parameters/#arraytype>Template Parameter Requirements</a> for the full list of requirements.</dd> <dt><code>AllocatorType</code></dt> <dd>the allocator to use for objects (e.g., <code>std::allocator</code>)</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>ArrayType</code> (<code>std::vector</code>) and <code>AllocatorType</code> (<code>std::allocator</code>), the default value for <code>array_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span>
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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> arrays.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> arrays as follows:</p> <blockquote> <p>An array is an ordered sequence of zero or more values.</p> </blockquote> <p>To store objects in C++, a type is defined by the template parameters explained below.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ArrayType</code></dt> <dd>container type to store arrays. It must be a vector-like container: the library uses <code>operator[]</code>, <code>at()</code>, and <code>resize()</code>, and requires random-access iterators. <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span></code> and <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> qualify; <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span></code> does not. See <a href=../../../features/types/template_parameters/#arraytype>Template Parameter Requirements</a> for the full list of requirements.</dd> <dt><code>AllocatorType</code></dt> <dd>the allocator to use for objects (e.g., <code>std::allocator</code>)</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>ArrayType</code> (<code>std::vector</code>) and <code>AllocatorType</code> (<code>std::allocator</code>), the default type for <code>array_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span>
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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>// value_type</span>
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<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>allocator</span><span class=o><</span><span class=n>basic_json</span><span class=o>></span><span class=w> </span><span class=c1>// allocator_type</span>
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<span class=o>></span>
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@@ -14,4 +14,4 @@
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<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><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>json</span><span class=o>></span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>array_t</span><span class=o>>::</span><span class=n>value</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
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<span class=p>}</span>
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</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../object_t/ >object_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects</li> <li><a href=../binary_t/ >binary_t</a> the type used to store binary values</li> <li><a href=../is_array/ >is_array</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is an array</li> <li><a href=../max_size/ >max_size</a> returns the maximum possible number of elements</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Made <code>capacity()</code> optional, so that array types such as <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> can be used, in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- 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 - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14Line truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../object_t/ >object_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects</li> <li><a href=../binary_t/ >binary_t</a> the type used to store binary values</li> <li><a href=../is_array/ >is_array</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is an array</li> <li><a href=../max_size/ >max_size</a> returns the maximum possible number of elements</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Made <code>capacity()</code> optional, so that array types such as <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> can be used, in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- 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 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 Line truncated
|
||||
@@ -22,7 +22,7 @@ To store objects in C++, a type is defined by the template parameters explained
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `ArrayType` (`std::vector`) and `AllocatorType` (`std::allocator`), the default value for `array_t` is:
|
||||
With the default values for `ArrayType` (`std::vector`) and `AllocatorType` (`std::allocator`), the default type for `array_t` is:
|
||||
|
||||
```
|
||||
std::vector<
|
||||
|
||||
@@ -23,7 +23,7 @@ To store boolean values in C++, a type is defined by the template parameter `Bo
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `BooleanType` (`#!cpp bool`), the default value for `boolean_t` is `#!cpp bool`.
|
||||
With the default values for `BooleanType` (`#!cpp bool`), the default type for `boolean_t` is `#!cpp bool`.
|
||||
|
||||
### Storage
|
||||
|
||||
|
||||
@@ -1,5 +1,5 @@
|
||||
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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></sLine truncated
|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> booleans.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code class=highlight><span class=kc>true</span></code> and <code class=highlight><span class=kc>false</span></code>.</p> <p>To store boolean values in C++, a type is defined by the template parameter <code>BooleanType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>BooleanType</code></dt> <dd>the type to store booleans. As it is stored directly inside a <code>basic_json</code> value (in a union), it must be a trivially default-constructible, trivially copyable, and trivially destructible type that is convertible to and from <code class=highlight><span class=kt>bool</span></code>. See <a href=../../../features/types/template_parameters/#booleantype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>BooleanType</code> (<code class=highlight><span class=kt>bool</span></code>), the default value for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>boolean_t</code> is by default, a typedef to <code class=highlight><span class=kt>bool</span></code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> booleans.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code class=highlight><span class=kc>true</span></code> and <code class=highlight><span class=kc>false</span></code>.</p> <p>To store boolean values in C++, a type is defined by the template parameter <code>BooleanType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>BooleanType</code></dt> <dd>the type to store booleans. As it is stored directly inside a <code>basic_json</code> value (in a union), it must be a trivially default-constructible, trivially copyable, and trivially destructible type that is convertible to and from <code class=highlight><span class=kt>bool</span></code>. See <a href=../../../features/types/template_parameters/#booleantype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>BooleanType</code> (<code class=highlight><span class=kt>bool</span></code>), the default type for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>boolean_t</code> is by default, a typedef to <code class=highlight><span class=kt>bool</span></code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -10,4 +10,4 @@
|
||||
<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><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o><</span><span class=kt>bool</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>boolean_t</span><span class=o>>::</span><span class=n>value</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../is_boolean/ >is_boolean</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a boolean</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 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 - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 384 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/liLine truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../is_boolean/ >is_boolean</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a boolean</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 384 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/Line truncated
|
||||
@@ -18,7 +18,7 @@ To store boolean values in C++, a type is defined by the template parameter `Boo
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `BooleanType` (`bool`), the default value for `boolean_t` is `bool`.
|
||||
With the default values for `BooleanType` (`bool`), the default type for `boolean_t` is `bool`.
|
||||
|
||||
### Storage
|
||||
|
||||
|
||||
@@ -62,6 +62,9 @@ Linear.
|
||||
|
||||
## Notes
|
||||
|
||||
Floating-point numbers are written with the fewest digits that read back as the same value (for `#!cpp double`; see
|
||||
[number handling](../../features/types/number_handling.md#number-serialization)).
|
||||
|
||||
Binary values are serialized as an object containing two keys:
|
||||
|
||||
- "bytes": an array of bytes as integers
|
||||
@@ -200,3 +203,5 @@ Binary values are serialized as an object containing two keys:
|
||||
- Error handlers added in version 3.4.0.
|
||||
- Serialization of binary values added in version 3.8.0.
|
||||
- Error handler `keep` added in version 3.13.0.
|
||||
- Doubles are written with the shortest digits (Żmij instead of Grisu2) since version 3.13.0; about 0.1% of doubles are
|
||||
written differently, most of them with fewer digits.
|
||||
@@ -2,7 +2,7 @@
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=w> </span><span class=n>indent_char</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sc>' '</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ensure_ascii</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>error_handler_t</span><span class=w> </span><span class=n>error_handler</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>error_handler_t</span><span class=o>::</span><span class=n>strict</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
|
||||
</code></pre></div> <p>Serialization function for <abbr title="JavaScript Object Notation">JSON</abbr> values. The function tries to mimic Python's <a href="https://docs.python.org/2/library/json.html#json.dump"><code>json.dumps()</code> function</a>, and currently supports its <code>indent</code> and <code>ensure_ascii</code> parameters.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>indent</code> (in)</dt> <dd>If <code>indent</code> is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of <code>0</code> will only insert newlines. <code>-1</code> (the default) selects the most compact representation.</dd> <dt><code>indent_char</code> (in)</dt> <dd>The character to use for indentation if <code>indent</code> is greater than <code>0</code>. The default is <code></code> (space).</dd> <dt><code>ensure_ascii</code> (in)</dt> <dd>If <code>ensure_ascii</code> is true, all non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters in the output are escaped with <code>\uXXXX</code> sequences, and the result consists of <abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters only.</dd> <dt><code>error_handler</code> (in)</dt> <dd>how to react on decoding errors; there are four possible values (see <a href=../error_handler_t/ ><code>error_handler_t</code></a>: <code>strict</code> (throws an exception in case a decoding error occurs; default), <code>replace</code> (replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD), <code>ignore</code> (ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences during serialization; all valid bytes are copied to the output unchanged, and invalid bytes are dropped), and <code>keep</code> (write the ill-formed bytes to the output as is, without escaping them, even if <code>ensure_ascii</code> is <code class=highlight><span class=nb>true</span></code>; the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, but equals the input bytes exactly, and well-formed characters around the ill-formed bytes are still escaped as usual)).</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>string containing the serialization of the <abbr title="JavaScript Object Notation">JSON</abbr> value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> if a string stored inside the <abbr title="JavaScript Object Notation">JSON</abbr> value is not <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoded and <code>error_handler</code> is set to <code>strict</code></p> <div class="admonition warning"> <p class=admonition-title>Serializing untrusted input</p> <p>When serializing values that may contain invalid or untrusted <abbr title="Unicode Transformation Format">UTF</abbr>-8 (e.g., bytes taken directly from network input), <code>dump()</code> throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> in the default <code>strict</code> mode. To serialize such data without throwing, pass <a href=../error_handler_t/ ><code>error_handler_t::replace</code></a> (substitutes U+FFFD) or <a href=../error_handler_t/ ><code>error_handler_t::ignore</code></a>. Callers that serialize untrusted input on a crash-sensitive path should either choose a non-strict error handler or wrap <code>dump()</code> in a <code class=highlight><span class=k>try</span></code>/<code class=highlight><span class=k>catch</span></code>.</p> <p>See the <a href=../../../home/faq/#serializing-untrusted-or-invalid-utf-8><abbr title="Frequently Asked Questions">FAQ</abbr></a> for details.</p> </div> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Binary values are serialized as an object containing two keys:</p> <ul> <li>"bytes": an array of bytes as integers</li> <li>"subtype": the subtype as integer or <code class=highlight><span class=kc>null</span></code> if the binary has no subtype</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following example shows the effect of different <code>indent</code>, <code>indent_char</code>, and <code>ensure_Line truncated
|
||||
</code></pre></div> <p>Serialization function for <abbr title="JavaScript Object Notation">JSON</abbr> values. The function tries to mimic Python's <a href="https://docs.python.org/2/library/json.html#json.dump"><code>json.dumps()</code> function</a>, and currently supports its <code>indent</code> and <code>ensure_ascii</code> parameters.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>indent</code> (in)</dt> <dd>If <code>indent</code> is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of <code>0</code> will only insert newlines. <code>-1</code> (the default) selects the most compact representation.</dd> <dt><code>indent_char</code> (in)</dt> <dd>The character to use for indentation if <code>indent</code> is greater than <code>0</code>. The default is <code></code> (space).</dd> <dt><code>ensure_ascii</code> (in)</dt> <dd>If <code>ensure_ascii</code> is true, all non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters in the output are escaped with <code>\uXXXX</code> sequences, and the result consists of <abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters only.</dd> <dt><code>error_handler</code> (in)</dt> <dd>how to react on decoding errors; there are four possible values (see <a href=../error_handler_t/ ><code>error_handler_t</code></a>: <code>strict</code> (throws an exception in case a decoding error occurs; default), <code>replace</code> (replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD), <code>ignore</code> (ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences during serialization; all valid bytes are copied to the output unchanged, and invalid bytes are dropped), and <code>keep</code> (write the ill-formed bytes to the output as is, without escaping them, even if <code>ensure_ascii</code> is <code class=highlight><span class=nb>true</span></code>; the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, but equals the input bytes exactly, and well-formed characters around the ill-formed bytes are still escaped as usual)).</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>string containing the serialization of the <abbr title="JavaScript Object Notation">JSON</abbr> value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> if a string stored inside the <abbr title="JavaScript Object Notation">JSON</abbr> value is not <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoded and <code>error_handler</code> is set to <code>strict</code></p> <div class="admonition warning"> <p class=admonition-title>Serializing untrusted input</p> <p>When serializing values that may contain invalid or untrusted <abbr title="Unicode Transformation Format">UTF</abbr>-8 (e.g., bytes taken directly from network input), <code>dump()</code> throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> in the default <code>strict</code> mode. To serialize such data without throwing, pass <a href=../error_handler_t/ ><code>error_handler_t::replace</code></a> (substitutes U+FFFD) or <a href=../error_handler_t/ ><code>error_handler_t::ignore</code></a>. Callers that serialize untrusted input on a crash-sensitive path should either choose a non-strict error handler or wrap <code>dump()</code> in a <code class=highlight><span class=k>try</span></code>/<code class=highlight><span class=k>catch</span></code>.</p> <p>See the <a href=../../../home/faq/#serializing-untrusted-or-invalid-utf-8><abbr title="Frequently Asked Questions">FAQ</abbr></a> for details.</p> </div> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Floating-point numbers are written with the fewest digits that read back as the same value (for <code class=highlight><span class=kt>double</span></code>; see <a href=../../../features/types/number_handling/#number-serialization>number handling</a>).</p> <p>Binary values are serialized as an object containing two keys:</p> <ul> <li>"bytes": an array of bytes as integers</li> <li>"subtype": the subtype as integer or <code class=highlight><span class=kc>null</span></code> if the binary has no subtype</li> </ul> <h2 id=exaLine truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
@@ -105,4 +105,4 @@
|
||||
<span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.</span><span class=kc>t</span><span class=err>ype_error.</span><span class=mi>316</span><span class=p>]</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>UTF</span><span class=mi>-8</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=w> </span><span class=err>a</span><span class=kc>t</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>dex</span><span class=w> </span><span class=mi>2</span><span class=p>:</span><span class=w> </span><span class=mi>0</span><span class=err>xA</span><span class=mi>9</span>
|
||||
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>replaced</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"ä�ü"</span>
|
||||
<span class=err>s</span><span class=kc>tr</span><span class=err>i</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>wi</span><span class=kc>t</span><span class=err>h</span><span class=w> </span><span class=err>ig</span><span class=kc>n</span><span class=err>ored</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>charac</span><span class=kc>ters</span><span class=p>:</span><span class=w> </span><span class=s2>"äü"</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_string/ >to_string</a> returns a string representation of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../operator_ltlt/ >operator<<</a> serialize to stream</li> <li><a href=../../../features/serialization/ >Serialization</a> - the serialization article</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Indentation character <code>indent_char</code>, option <code>ensure_ascii</code> and exceptions added in version 3.0.0.</li> <li>Error handlers added in version 3.4.0.</li> <li>Serialization of binary values added in version 3.8.0.</li> <li>Error handler <code>keep</code> added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 10:13:49 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416cLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../to_string/ >to_string</a> returns a string representation of a <abbr title="JavaScript Object Notation">JSON</abbr> value</li> <li><a href=../../operator_ltlt/ >operator<<</a> serialize to stream</li> <li><a href=../../../features/serialization/ >Serialization</a> - the serialization article</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Indentation character <code>indent_char</code>, option <code>ensure_ascii</code> and exceptions added in version 3.0.0.</li> <li>Error handlers added in version 3.4.0.</li> <li>Serialization of binary values added in version 3.8.0.</li> <li>Error handler <code>keep</code> added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Doubles are written with the shortest digits (Żmij instead of Grisu2) since version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; about 0.1% of doubles are written differently, most of them with fewer digits.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 15:38:37 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 4Line truncated
|
||||
@@ -43,6 +43,8 @@ Linear.
|
||||
|
||||
## Notes
|
||||
|
||||
Floating-point numbers are written with the fewest digits that read back as the same value (for `double`; see [number handling](https://json.nlohmann.me/features/types/number_handling/#number-serialization)).
|
||||
|
||||
Binary values are serialized as an object containing two keys:
|
||||
|
||||
- "bytes": an array of bytes as integers
|
||||
@@ -178,3 +180,4 @@ string with ignored invalid characters: "äü"
|
||||
- Error handlers added in version 3.4.0.
|
||||
- Serialization of binary values added in version 3.8.0.
|
||||
- Error handler `keep` added in version 3.13.0 unreleased.
|
||||
- Doubles are written with the shortest digits (Żmij instead of Grisu2) since version 3.13.0 unreleased; about 0.1% of doubles are written differently, most of them with fewer digits.
|
||||
@@ -12,7 +12,7 @@
|
||||
<span class=w> </span><span class=k>class</span><span class=w> </span><span class=nc>CustomBaseClass</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=kt>void</span>
|
||||
<span class=o>></span>
|
||||
<span class=k>class</span><span class=w> </span><span class=nc>basic_json</span><span class=p>;</span>
|
||||
</code></pre></div> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <table> <thead> <tr> <th>Template parameter</th> <th>Description</th> <th>Derived type</th> </tr> </thead> <tbody> <tr> <td><code>ObjectType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> objects</td> <td><a href=object_t/ ><code>object_t</code></a></td> </tr> <tr> <td><code>ArrayType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> arrays</td> <td><a href=array_t/ ><code>array_t</code></a></td> </tr> <tr> <td><code>StringType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> strings and object keys</td> <td><a href=string_t/ ><code>string_t</code></a></td> </tr> <tr> <td><code>BooleanType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> booleans</td> <td><a href=boolean_t/ ><code>boolean_t</code></a></td> </tr> <tr> <td><code>NumberIntegerType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> integer numbers</td> <td><a href=number_integer_t/ ><code>number_integer_t</code></a></td> </tr> <tr> <td><code>NumberUnsignedType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> unsigned integer numbers</td> <td><a href=number_unsigned_t/ ><code>number_unsigned_t</code></a></td> </tr> <tr> <td><code>NumberFloatType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> floating-point numbers</td> <td><a href=number_float_t/ ><code>number_float_t</code></a></td> </tr> <tr> <td><code>AllocatorType</code></td> <td>type of the allocator to use</td> <td></td> </tr> <tr> <td><code>JSONSerializer</code></td> <td>the serializer to resolve internal calls to <code>to_json()</code> and <code>from_json()</code></td> <td><a href=json_serializer/ ><code>json_serializer</code></a></td> </tr> <tr> <td><code>BinaryType</code></td> <td>type for binary arrays</td> <td><a href=binary_t/ ><code>binary_t</code></a></td> </tr> <tr> <td><code>CustomBaseClass</code></td> <td>extension point for user code</td> <td><a href=json_base_class_t/ ><code>json_base_class_t</code></a></td> </tr> </tbody> </table> <p>The library imposes a number of requirements on these types that are not expressed as C++ concepts, such as the container operations <code>object_t</code> and <code>array_t</code> must provide, or the fact that <code>StringType</code> must be <code>char</code>-based. They are collected in <a href=../../features/types/template_parameters/ >Template Parameter Requirements</a>.</p> <h2 id=specializations>Specializations<a class=headerlink href=#specializations title="Permanent link">¶</a></h2> <ul> <li><a href=../json/ ><strong>json</strong></a> - default specialization</li> <li><a href=../ordered_json/ ><strong>ordered_json</strong></a> - a specialization that maintains the insertion order of object keys</li> </ul> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">¶</a></h2> <p>All operations that add values to an <strong>array</strong> (<a href=push_back/ ><code>push_back</code></a> , <a href=operator%2B%3D/ ><code>operator+=</code></a>, <a href=emplace_back/ ><code>emplace_back</code></a>, <a href=insert/ ><code>insert</code></a>, and <a href=operator%5B%5D/ ><code>operator[]</code></a> for a non-existing index) can yield a reallocation, in which case all iterators (including the <a href=end/ ><code>end()</code></a> iterator) and all references to the elements are invalidated.</p> <p>For <a href=../ordered_json/ ><code>ordered_json</code></a>, also all operations that add a value to an <strong>object</strong> (<a href=push_back/ ><code>push_back</code></a>, <a href=operator%2B%3D/ ><code>operator+=</code></a>, <a href=emplace/ ><code>emplace</code></a>, <a href=insert/ ><code>insert</code></a>, <a href=update/ ><code>update</code></a>, and <a href=operator%5B%5D/ ><code>operator[]</code></a> for a non-existing key) can yield a reallocation, in which case all iterators (including the <a href=end/ ><code>end()</code></a> iterator) and all references to the elements are invalidated.</p> <h2 id=requirements>Requirements<a class=headerlink href=#requirements title="Permanent link">¶</a></h2> <p>The class satisfies the following concept requirements:</p> <h3 id=basic>Basic<a class=headerlink href=#basic title="Permanent link">¶</a></h3> <ul> <li><a href="https://en.cppreference.com/w/cpp/named_req/DefaultConstructible">DefaultConstructible</a>: <abbr title="JavaScript Object Notation">JSON</abbr> values can be default-constructed. The result will be a <abbr title="JavaScript Object Notation">JSON</abbr> null value.</li> <li><a href="https://en.cppreference.com/w/cpp/named_req/MoveConstructible">MoveConstructible</a>: A <abbr title="JavaScript Object Notation">JSON</abbr> value can be constructed from an rvalue arLine truncated
|
||||
</code></pre></div> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <table> <thead> <tr> <th>Template parameter</th> <th>Description</th> <th>Derived type</th> </tr> </thead> <tbody> <tr> <td><code>ObjectType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> objects</td> <td><a href=object_t/ ><code>object_t</code></a></td> </tr> <tr> <td><code>ArrayType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> arrays</td> <td><a href=array_t/ ><code>array_t</code></a></td> </tr> <tr> <td><code>StringType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> strings and object keys</td> <td><a href=string_t/ ><code>string_t</code></a></td> </tr> <tr> <td><code>BooleanType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> booleans</td> <td><a href=boolean_t/ ><code>boolean_t</code></a></td> </tr> <tr> <td><code>NumberIntegerType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> integer numbers</td> <td><a href=number_integer_t/ ><code>number_integer_t</code></a></td> </tr> <tr> <td><code>NumberUnsignedType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> unsigned integer numbers</td> <td><a href=number_unsigned_t/ ><code>number_unsigned_t</code></a></td> </tr> <tr> <td><code>NumberFloatType</code></td> <td>type for <abbr title="JavaScript Object Notation">JSON</abbr> floating-point numbers</td> <td><a href=number_float_t/ ><code>number_float_t</code></a></td> </tr> <tr> <td><code>AllocatorType</code></td> <td>type of the allocator to use</td> <td></td> </tr> <tr> <td><code>JSONSerializer</code></td> <td>the serializer to resolve internal calls to <code>to_json()</code> and <code>from_json()</code></td> <td><a href=json_serializer/ ><code>json_serializer</code></a></td> </tr> <tr> <td><code>BinaryType</code></td> <td>type for binary arrays</td> <td><a href=binary_t/ ><code>binary_t</code></a></td> </tr> <tr> <td><code>CustomBaseClass</code></td> <td>extension point for user code</td> <td><a href=json_base_class_t/ ><code>json_base_class_t</code></a></td> </tr> </tbody> </table> <p>The library imposes a number of requirements on these types that are not expressed as C++ concepts, such as the container operations <code>object_t</code> and <code>array_t</code> must provide, or the fact that <code>StringType</code> must be <code>char</code>-based. They are collected in <a href=../../features/types/template_parameters/ >Template Parameter Requirements</a>.</p> <h2 id=specializations>Specializations<a class=headerlink href=#specializations title="Permanent link">¶</a></h2> <ul> <li><a href=../json/ ><strong>json</strong></a> - default specialization</li> <li><a href=../ordered_json/ ><strong>ordered_json</strong></a> - a specialization that maintains the insertion order of object keys</li> </ul> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">¶</a></h2> <p>All operations that add values to an <strong>array</strong> (<a href=push_back/ ><code>push_back</code></a> , <a href=operator%2B%3D/ ><code>operator+=</code></a>, <a href=emplace_back/ ><code>emplace_back</code></a>, <a href=insert/ ><code>insert</code></a>, and <a href=operator%5B%5D/ ><code>operator[]</code></a> for a non-existing index) can yield a reallocation, in which case all iterators (including the <a href=end/ ><code>end()</code></a> iterator) and all references to the elements are invalidated.</p> <p>For <a href=../ordered_json/ ><code>ordered_json</code></a>, also all operations that add a value to an <strong>object</strong> (<a href=push_back/ ><code>push_back</code></a>, <a href=operator%2B%3D/ ><code>operator+=</code></a>, <a href=emplace/ ><code>emplace</code></a>, <a href=insert/ ><code>insert</code></a>, <a href=update/ ><code>update</code></a>, and <a href=operator%5B%5D/ ><code>operator[]</code></a> for a non-existing key) can yield a reallocation, in which case all iterators (including the <a href=end/ ><code>end()</code></a> iterator) and all references to the elements are invalidated.</p> <h2 id=requirements>Requirements<a class=headerlink href=#requirements title="Permanent link">¶</a></h2> <p>The class satisfies the following concept requirements:</p> <h3 id=basic>Basic<a class=headerlink href=#basic title="Permanent link">¶</a></h3> <ul> <li><a href="https://en.cppreference.com/w/cpp/named_req/DefaultConstructible">DefaultConstructible</a>: <abbr title="JavaScript Object Notation">JSON</abbr> values can be default-constructed. The result will be a <abbr title="JavaScript Object Notation">JSON</abbr> null value.</li> <li><a href="https://en.cppreference.com/w/cpp/named_req/MoveConstructible">MoveConstructible</a>: A <abbr title="JavaScript Object Notation">JSON</abbr> value can be constructed from an rvalue arLine truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -78,4 +78,4 @@
|
||||
<span class=w> </span><span class=nt>"pi"</span><span class=p>:</span><span class=w> </span><span class=mf>3.141</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"size"</span><span class=p>:</span><span class=w> </span><span class=mi>8</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259: The JavaScript Object Notation (<abbr title="JavaScript Object Notation">JSON</abbr>) Data Interchange Format</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 12, 2026 07:33:43 UTC">October 12, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 384 512"><!-- Font Awesome Free Line truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259: The JavaScript Object Notation (<abbr title="JavaScript Object Notation">JSON</abbr>) Data Interchange Format</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 15:40:55 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29.2h.9c8.9-16.8 30.6-34.5 62.9-34.5 67.2 0 79.7 44.3 79.7 101.9z"/></svg> </a> <a href="https://www.xing.com/profile/Niels_Lohmann" target="_blank" rel="noopener" title="www.xing.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 384 512"><!-- Font Awesome Free Line truncated
|
||||
@@ -68,7 +68,7 @@ The class satisfies the following concept requirements:
|
||||
### Library-wide
|
||||
|
||||
- [EqualityComparable](https://en.cppreference.com/w/cpp/named_req/EqualityComparable): JSON values can be compared with `==`, see [`operator==`](https://json.nlohmann.me/api/basic_json/operator_eq/index.md).
|
||||
- [LessThanComparable](https://en.cppreference.com/w/cpp/named_req/LessThanComparable): JSON values can be compared with `<`, see [`operator<`](https://json.nlohmann.me/api/basic_json/operator_le/index.md).
|
||||
- [LessThanComparable](https://en.cppreference.com/w/cpp/named_req/LessThanComparable): JSON values can be compared with `<`, see [`operator<`](https://json.nlohmann.me/api/basic_json/operator_lt/index.md).
|
||||
- [Swappable](https://en.cppreference.com/w/cpp/named_req/Swappable): Any JSON lvalue or rvalue of can be swapped with any lvalue or rvalue of other compatible types, using unqualified function `swap`.
|
||||
- [NullablePointer](https://en.cppreference.com/w/cpp/named_req/NullablePointer): JSON values can be compared against `std::nullptr_t` objects which are used to model the `null` value.
|
||||
|
||||
|
||||
@@ -11,7 +11,7 @@ added members with their new values, and removed members with the value `#!json
|
||||
member by member; any other value that differs, including an array, is replaced as a whole.
|
||||
|
||||
For two JSON values `source` and `target`, where `target` contains no object member whose value is `#!json null`, the
|
||||
following code always yields `#!cpp true`:
|
||||
following code always yields `#!cpp true` (for [`ordered_json`](../ordered_json.md), see the notes below):
|
||||
```cpp
|
||||
basic_json patched = source;
|
||||
patched.merge_patch(merge_diff(source, target));
|
||||
|
||||
@@ -1,6 +1,6 @@
|
||||
<!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/merge_diff/" rel="canonical"><link href=../meta/ rel=prev><link href=../merge_patch/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>merge_diff - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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|
||||
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json</span><span class=o>&</span><span class=w> </span><span class=n>target</span><span class=p>);</span>
|
||||
</code></pre></div> <p>Creates a <a href="https://tools.ietf.org/html/rfc7396"><abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</a> so that value <code>source</code> can be changed into the value <code>target</code> by calling the <a href=../merge_patch/ ><code>merge_patch</code></a> function. The patch contains only what differs: changed and added members with their new values, and removed members with the value <code class=highlight><span class=kc>null</span></code>. Nested objects are compared member by member; any other value that differs, including an array, is replaced as a whole.</p> <p>For two <abbr title="JavaScript Object Notation">JSON</abbr> values <code>source</code> and <code>target</code>, where <code>target</code> contains no object member whose value is <code class=highlight><span class=kc>null</span></code>, the following code always yields <code class=highlight><span class=nb>true</span></code>: <div class=highlight><pre><span></span><code><span class=n>basic_json</span><span class=w> </span><span class=n>patched</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>source</span><span class=p>;</span>
|
||||
</code></pre></div> <p>Creates a <a href="https://tools.ietf.org/html/rfc7396"><abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</a> so that value <code>source</code> can be changed into the value <code>target</code> by calling the <a href=../merge_patch/ ><code>merge_patch</code></a> function. The patch contains only what differs: changed and added members with their new values, and removed members with the value <code class=highlight><span class=kc>null</span></code>. Nested objects are compared member by member; any other value that differs, including an array, is replaced as a whole.</p> <p>For two <abbr title="JavaScript Object Notation">JSON</abbr> values <code>source</code> and <code>target</code>, where <code>target</code> contains no object member whose value is <code class=highlight><span class=kc>null</span></code>, the following code always yields <code class=highlight><span class=nb>true</span></code> (for <a href=../../ordered_json/ ><code>ordered_json</code></a>, see the notes below): <div class=highlight><pre><span></span><code><span class=n>basic_json</span><span class=w> </span><span class=n>patched</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>source</span><span class=p>;</span>
|
||||
<span class=n>patched</span><span class=p>.</span><span class=n>merge_patch</span><span class=p>(</span><span class=n>merge_diff</span><span class=p>(</span><span class=n>source</span><span class=p>,</span><span class=w> </span><span class=n>target</span><span class=p>));</span>
|
||||
<span class=n>patched</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>target</span><span class=p>;</span>
|
||||
</code></pre></div></p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>source</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to compare from</dd> <dt><code>target</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to compare against</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch to convert the <code>source</code> to <code>target</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: <code>source</code> and <code>target</code> are never modified.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the total number of values (including nested ones) in <code>source</code> and <code>target</code>, times the cost of a key-based object operation (looking up a key, or adding one to the patch): logarithmic for <a href=../../json/ ><code>json</code></a>, and linear for <a href=../../ordered_json/ ><code>ordered_json</code></a> (see <a href=../../ordered_map/#complexity><code>ordered_map</code> complexity</a>). For <code>ordered_json</code>, diffing two objects with <code>n</code> and <code>m</code> members therefore takes O((n+m)²).</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <ul> <li>A merge patch uses <code class=highlight><span class=kc>null</span></code> to remove a member, so it cannot set a member to <code class=highlight><span class=kc>null</span></code>. As in <abbr title="Request for Comments">RFC</abbr> 7396, a <code class=highlight><span class=kc>null</span></code> member of <code>target</code> is treated as absent: the patch removes the member from <code>source</code> instead of setting it to <code class=highlight><span class=kc>null</span></code>. A member that is <code class=highlight><span class=kc>null</span></code> in both <code>source</code> and <code>target</code> is unchanged and left out of the patch, so <code>source</code> keeps it.</li> <li>A merge patch cannot reorder object members, and <a href=../merge_patch/ ><code>merge_patch</code></a> appends added members at the end. For <a href=../../ordered_json/ ><code>ordered_json</code></a>, the patched value therefore has the same members as <code>target</code>, but not necessarily in the same order, and may compare unequal to it. The patch lists changed and removed members in the order of <code>source</code>, followed by added members in the order of <code>target</code>.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch is created as a diff for two <abbr title="JavaScript Object Notation">JSON</abbr> values.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
@@ -76,4 +76,4 @@
|
||||
<span class=w> </span><span class=p>],</span>
|
||||
<span class=w> </span><span class=nt>"title"</span><span class=p>:</span><span class=w> </span><span class=s2>"Hello!"</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc7396"><abbr title="Request for Comments">RFC</abbr> 7396 (<abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch)</a></li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../diff/ >diff</a> creates a diff as a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 12, 2026 07:33:43 UTC">October 12, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416Line truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc7396"><abbr title="Request for Comments">RFC</abbr> 7396 (<abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch)</a></li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../diff/ >diff</a> creates a diff as a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- 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 14, 2026 15:40:55 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416Line truncated
|
||||
@@ -7,7 +7,7 @@ static basic_json merge_diff(const basic_json& source,
|
||||
|
||||
Creates a [JSON Merge Patch](https://tools.ietf.org/html/rfc7396) so that value `source` can be changed into the value `target` by calling the [`merge_patch`](https://json.nlohmann.me/api/basic_json/merge_patch/index.md) function. The patch contains only what differs: changed and added members with their new values, and removed members with the value `null`. Nested objects are compared member by member; any other value that differs, including an array, is replaced as a whole.
|
||||
|
||||
For two JSON values `source` and `target`, where `target` contains no object member whose value is `null`, the following code always yields `true`:
|
||||
For two JSON values `source` and `target`, where `target` contains no object member whose value is `null`, the following code always yields `true` (for [`ordered_json`](https://json.nlohmann.me/api/ordered_json/index.md), see the notes below):
|
||||
|
||||
```
|
||||
basic_json patched = source;
|
||||
|
||||
@@ -23,9 +23,10 @@ type to use.
|
||||
## Template parameters
|
||||
|
||||
`NumberFloatType`
|
||||
: the type to store floating-point numbers. Parsing and serialization are implemented in terms of
|
||||
`#!cpp std::strtof`/`#!cpp std::strtod`/`#!cpp std::strtold` and `#!cpp std::snprintf`, so the type must be
|
||||
`#!cpp float`, `#!cpp double`, or `#!cpp long double`. The
|
||||
: the type to store floating-point numbers. The type must be `#!cpp float`, `#!cpp double`, or
|
||||
`#!cpp long double`. The parser converts `#!cpp float`, `#!cpp double`, and a `#!cpp long double` that is IEEE 754
|
||||
binary64 itself. It converts other `#!cpp long double` formats with `#!cpp std::from_chars` where available, or
|
||||
with `#!cpp std::strtold` otherwise. Serialization falls back to `#!cpp std::snprintf`. The
|
||||
[binary formats](../../features/binary_formats/index.md) additionally require `#!cpp float` or `#!cpp double`,
|
||||
because they have no encoding for `#!cpp long double`. See
|
||||
[Template Parameter Requirements](../../features/types/template_parameters.md#numberfloattype).
|
||||
@@ -34,7 +35,7 @@ type to use.
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `NumberFloatType` (`double`), the default value for `number_float_t` is `#!cpp double`.
|
||||
With the default values for `NumberFloatType` (`double`), the default type for `number_float_t` is `#!cpp double`.
|
||||
|
||||
### Default behavior
|
||||
|
||||
@@ -51,9 +52,11 @@ With the default values for `NumberFloatType` (`double`), the default value for
|
||||
> interoperability can be achieved by implementations that expect no more precision or range than these provide, in the
|
||||
> sense that implementations will approximate JSON numbers within the expected precision.
|
||||
|
||||
This implementation does exactly follow this approach, as it uses double precision floating-point numbers. Note values
|
||||
smaller than `-1.79769313486232e+308` and values greater than `1.79769313486232e+308` will be stored as NaN internally
|
||||
and be serialized to `null`.
|
||||
This implementation does exactly follow this approach, as it uses double precision floating-point numbers by default.
|
||||
Note that with the default `double`, numbers smaller than `-1.79769313486232e+308` or greater than
|
||||
`1.79769313486232e+308` are rejected during parsing with
|
||||
[`out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406). Non-finite values (NaN and infinity) can
|
||||
only be stored by assigning them directly and are serialized to `null`.
|
||||
|
||||
During deserialization (from JSON text or any of the binary formats), a finite number that does not fit into
|
||||
`number_float_t` is rejected with [`out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406), for
|
||||
|
||||
@@ -1,5 +1,5 @@
|
||||
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||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> numbers (floating-point).</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and <abbr title="Not a Number">NaN</abbr>) are not permitted.</p> </blockquote> <p>This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer, or a floating-point number. Therefore, three different types, <a href=../number_integer_t/ ><code>number_integer_t</code></a>, <a href=../number_unsigned_t/ ><code>number_unsigned_t</code></a> and <code>number_float_t</code> are used.</p> <p>To store floating-point numbers in C++, a type is defined by the template parameter <code>NumberFloatType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>NumberFloatType</code></dt> <dd>the type to store floating-point numbers. Parsing and serialization are implemented in terms of <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>strtof</span></code>/<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>strtod</span></code>/<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>strtold</span></code> and <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>snprintf</span></code>, so the type must be <code class=highlight><span class=kt>float</span></code>, <code class=highlight><span class=kt>double</span></code>, or <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>. The <a href=../../../features/binary_formats/ >binary formats</a> additionally require <code class=highlight><span class=kt>float</span></code> or <code class=highlight><span class=kt>double</span></code>, because they have no encoding for <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>. See <a href=../../../features/types/template_parameters/#numberfloattype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>NumberFloatType</code> (<code>double</code>), the default value for <code>number_float_t</code> is <code class=highlight><span class=kt>double</span></code>.</p> <h3 id=default-behavior>Default behavior<a class=headerlink href=#default-behavior title="Permanent link">¶</a></h3> <ul> <li>The restrictions about leading zeros are not enforced in C++. Instead, leading zeros in floating-point literals will be ignored. Internally, the value will be stored as a decimal number. For instance, the C++ floating-point literal <code>01.2</code> will be serialized to <code>1.2</code>. During deserialization, leading zeros yield an error.</li> <li>Not-a-number (<abbr title="Not a Number">NaN</abbr>) values will be serialized to <code>null</code>.</li> </ul> <h3 id=limits>Limits<a class=headerlink href=#limits title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> states:</p> <blockquote> <p>This specification allows implementations to set limits on the range and precision of numbers accepted. Since software that implements <abbr title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 754-2008 binary64 (double precision) numbers is generally available and widely used, good interoperability can be achieved by implementations that expect no more precision or range than these provide, in the sense that implementations will approximate <abbr title="JavaScript Object Notation">JSON</abbr> numbers within the expected precision.</p> </blockquote> <p>This implementation does exactly follow this approach, as it uses double precision floating-point numbers. Note values smaller than <code>-1.79769313486232e+308</code> and values greater than <code>1.79769313486232e+308</code> will be stored as <abbr title="Not a Number">NaN</abbr> internally and be serialized to <code>null</code>.</p> <p>During deserialization (from <abbr title="JavaScript Object Notation">JSON</abbr> text or any of the bLine truncated
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||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> numbers (floating-point).</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and <abbr title="Not a Number">NaN</abbr>) are not permitted.</p> </blockquote> <p>This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer, or a floating-point number. Therefore, three different types, <a href=../number_integer_t/ ><code>number_integer_t</code></a>, <a href=../number_unsigned_t/ ><code>number_unsigned_t</code></a> and <code>number_float_t</code> are used.</p> <p>To store floating-point numbers in C++, a type is defined by the template parameter <code>NumberFloatType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>NumberFloatType</code></dt> <dd>the type to store floating-point numbers. The type must be <code class=highlight><span class=kt>float</span></code>, <code class=highlight><span class=kt>double</span></code>, or <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>. The parser converts <code class=highlight><span class=kt>float</span></code>, <code class=highlight><span class=kt>double</span></code>, and a <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code> that is <abbr title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 754 binary64 itself. It converts other <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code> formats with <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>from_chars</span></code> where available, or with <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>strtold</span></code> otherwise. Serialization falls back to <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>snprintf</span></code>. The <a href=../../../features/binary_formats/ >binary formats</a> additionally require <code class=highlight><span class=kt>float</span></code> or <code class=highlight><span class=kt>double</span></code>, because they have no encoding for <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>. See <a href=../../../features/types/template_parameters/#numberfloattype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>NumberFloatType</code> (<code>double</code>), the default type for <code>number_float_t</code> is <code class=highlight><span class=kt>double</span></code>.</p> <h3 id=default-behavior>Default behavior<a class=headerlink href=#default-behavior title="Permanent link">¶</a></h3> <ul> <li>The restrictions about leading zeros are not enforced in C++. Instead, leading zeros in floating-point literals will be ignored. Internally, the value will be stored as a decimal number. For instance, the C++ floating-point literal <code>01.2</code> will be serialized to <code>1.2</code>. During deserialization, leading zeros yield an error.</li> <li>Not-a-number (<abbr title="Not a Number">NaN</abbr>) values will be serialized to <code>null</code>.</li> </ul> <h3 id=limits>Limits<a class=headerlink href=#limits title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> states:</p> <blockquote> <p>This specification allows implementations to set limits on the range and precision of numbers accepted. Since software that implements <abbr title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 754-2008 binary64 (double precision) numbers is generally available and widely used, good interoperability can be achieved by implementations that expect no more precision or range than these provide, in the sense that implementations will approximate <abbr title="JavaScript Object Notation">JSON</abbr> numbers within the expected precision.</p> </blockquote> <p>This implementation does exactly follow this approLine truncated
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||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
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||||
@@ -10,4 +10,4 @@
|
||||
<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><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o><</span><span class=kt>double</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>number_float_t</span><span class=o>>::</span><span class=n>value</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../number_integer_t/ >number_integer_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> integer numbers</li> <li><a href=../number_unsigned_t/ >number_unsigned_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> unsigned integer numbers</li> <li><a href=../is_number_float/ >is_number_float</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a floating-point number</li> <li><a href=../../../features/types/number_handling/ >Number Handling</a> - the article on number handling</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 15:53:29 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V3Line truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../number_integer_t/ >number_integer_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> integer numbers</li> <li><a href=../number_unsigned_t/ >number_unsigned_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> unsigned integer numbers</li> <li><a href=../is_number_float/ >is_number_float</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a floating-point number</li> <li><a href=../../../features/types/number_handling/ >Number Handling</a> - the article on number handling</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4Line truncated
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@@ -16,13 +16,13 @@ To store floating-point numbers in C++, a type is defined by the template parame
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## Template parameters
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`NumberFloatType` : the type to store floating-point numbers. Parsing and serialization are implemented in terms of `std::strtof`/`std::strtod`/`std::strtold` and `std::snprintf`, so the type must be `float`, `double`, or `long double`. The [binary formats](https://json.nlohmann.me/features/binary_formats/index.md) additionally require `float` or `double`, because they have no encoding for `long double`. See [Template Parameter Requirements](https://json.nlohmann.me/features/types/template_parameters/#numberfloattype).
|
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`NumberFloatType` : the type to store floating-point numbers. The type must be `float`, `double`, or `long double`. The parser converts `float`, `double`, and a `long double` that is IEEE 754 binary64 itself. It converts other `long double` formats with `std::from_chars` where available, or with `std::strtold` otherwise. Serialization falls back to `std::snprintf`. The [binary formats](https://json.nlohmann.me/features/binary_formats/index.md) additionally require `float` or `double`, because they have no encoding for `long double`. See [Template Parameter Requirements](https://json.nlohmann.me/features/types/template_parameters/#numberfloattype).
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## Notes
|
||||
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### Default type
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||||
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With the default values for `NumberFloatType` (`double`), the default value for `number_float_t` is `double`.
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With the default values for `NumberFloatType` (`double`), the default type for `number_float_t` is `double`.
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### Default behavior
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@@ -35,7 +35,7 @@ With the default values for `NumberFloatType` (`double`), the default value for
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> This specification allows implementations to set limits on the range and precision of numbers accepted. Since software that implements IEEE 754-2008 binary64 (double precision) numbers is generally available and widely used, good interoperability can be achieved by implementations that expect no more precision or range than these provide, in the sense that implementations will approximate JSON numbers within the expected precision.
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This implementation does exactly follow this approach, as it uses double precision floating-point numbers. Note values smaller than `-1.79769313486232e+308` and values greater than `1.79769313486232e+308` will be stored as NaN internally and be serialized to `null`.
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This implementation does exactly follow this approach, as it uses double precision floating-point numbers by default. Note that with the default `double`, numbers smaller than `-1.79769313486232e+308` or greater than `1.79769313486232e+308` are rejected during parsing with [`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406). Non-finite values (NaN and infinity) can only be stored by assigning them directly and are serialized to `null`.
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During deserialization (from JSON text or any of the binary formats), a finite number that does not fit into `number_float_t` is rejected with [`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406), for example a double-precision number in a binary format when `number_float_t` is `float`.
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@@ -31,7 +31,7 @@ to use.
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### Default type
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With the default values for `NumberIntegerType` (`std::int64_t`), the default value for `number_integer_t` is
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With the default values for `NumberIntegerType` (`std::int64_t`), the default type for `number_integer_t` is
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`#!cpp std::int64_t`.
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### Default behavior
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@@ -1,5 +1,5 @@
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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> numbers (integers).</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and <abbr title="Not a Number">NaN</abbr>) are not permitted.</p> </blockquote> <p>This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer, or a floating-point number. Therefore, three different types, <code>number_integer_t</code>, <a href=../number_unsigned_t/ ><code>number_unsigned_t</code></a> and <a href=../number_float_t/ ><code>number_float_t</code></a> are used.</p> <p>To store integer numbers in C++, a type is defined by the template parameter <code>NumberIntegerType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>NumberIntegerType</code></dt> <dd>the type to store signed integers. It must be a <strong>signed integral</strong> type (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_integral</span></code>) with a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>numeric_limits</span></code> specialization, and it is stored directly inside a <code>basic_json</code> value. See <a href=../../../features/types/template_parameters/#numberintegertype-and-numberunsignedtype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>NumberIntegerType</code> (<code>std::int64_t</code>), the default value for <code>number_integer_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span></code>.</p> <h3 id=default-behavior>Default behavior<a class=headerlink href=#default-behavior title="Permanent link">¶</a></h3> <ul> <li>The restrictions about leading zeros are not enforced in C++. Instead, leading zeros in integer literals lead to an interpretation as an octal number. Internally, the value will be stored as a decimal number. For instance, the C++ integer literal <code>010</code> will be serialized to <code>8</code>. During deserialization, leading zeros yield an error.</li> </ul> <h3 id=limits>Limits<a class=headerlink href=#limits title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the range and precision of numbers.</p> </blockquote> <p>When the default type is used, the maximal integer number that can be stored is <code>9223372036854775807</code> (INT64_MAX) and the minimal integer number that can be stored is <code>-9223372036854775808</code> (INT64_MIN). Integer numbers that are out of range will yield over/underflow when used in a constructor. During deserialization (from <abbr title="JavaScript Object Notation">JSON</abbr> text or any of the binary formats), too large or small integer numbers will automatically be stored as <a href=../number_unsigned_t/ ><code>number_unsigned_t</code></a> or <a href=../number_float_t/ ><code>number_float_t</code></a>.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> further states:</p> <blockquote> <p>Note that when such software is used, numbers that are integers and are in the range [-2<sup>53</sup>+1, 2<sup>53</sup>-1] are interoperable in the sense that implementations will agree exactly on their numeric values.</p> </blockquote> <p>As this range is a subrange of the exactly supported range [INT64_MIN, INT64_MAX], this class's integer type is interoperable.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>Integer number values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>number_integer_t</code> is by default, a typedef to <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</spLine truncated
|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> numbers (integers).</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and <abbr title="Not a Number">NaN</abbr>) are not permitted.</p> </blockquote> <p>This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer, or a floating-point number. Therefore, three different types, <code>number_integer_t</code>, <a href=../number_unsigned_t/ ><code>number_unsigned_t</code></a> and <a href=../number_float_t/ ><code>number_float_t</code></a> are used.</p> <p>To store integer numbers in C++, a type is defined by the template parameter <code>NumberIntegerType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>NumberIntegerType</code></dt> <dd>the type to store signed integers. It must be a <strong>signed integral</strong> type (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_integral</span></code>) with a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>numeric_limits</span></code> specialization, and it is stored directly inside a <code>basic_json</code> value. See <a href=../../../features/types/template_parameters/#numberintegertype-and-numberunsignedtype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>NumberIntegerType</code> (<code>std::int64_t</code>), the default type for <code>number_integer_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span></code>.</p> <h3 id=default-behavior>Default behavior<a class=headerlink href=#default-behavior title="Permanent link">¶</a></h3> <ul> <li>The restrictions about leading zeros are not enforced in C++. Instead, leading zeros in integer literals lead to an interpretation as an octal number. Internally, the value will be stored as a decimal number. For instance, the C++ integer literal <code>010</code> will be serialized to <code>8</code>. During deserialization, leading zeros yield an error.</li> </ul> <h3 id=limits>Limits<a class=headerlink href=#limits title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the range and precision of numbers.</p> </blockquote> <p>When the default type is used, the maximal integer number that can be stored is <code>9223372036854775807</code> (INT64_MAX) and the minimal integer number that can be stored is <code>-9223372036854775808</code> (INT64_MIN). Integer numbers that are out of range will yield over/underflow when used in a constructor. During deserialization (from <abbr title="JavaScript Object Notation">JSON</abbr> text or any of the binary formats), too large or small integer numbers will automatically be stored as <a href=../number_unsigned_t/ ><code>number_unsigned_t</code></a> or <a href=../number_float_t/ ><code>number_float_t</code></a>.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> further states:</p> <blockquote> <p>Note that when such software is used, numbers that are integers and are in the range [-2<sup>53</sup>+1, 2<sup>53</sup>-1] are interoperable in the sense that implementations will agree exactly on their numeric values.</p> </blockquote> <p>As this range is a subrange of the exactly supported range [INT64_MIN, INT64_MAX], this class's integer type is interoperable.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>Integer number values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>number_integer_t</code> is by default, a typedef to <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</spaLine truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -10,4 +10,4 @@
|
||||
<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><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o><</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>json</span><span class=o>::</span><span class=n>number_integer_t</span><span class=o>>::</span><span class=n>value</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../number_unsigned_t/ >number_unsigned_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> unsigned integer numbers</li> <li><a href=../number_float_t/ >number_float_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> floating-point numbers</li> <li><a href=../is_number_integer/ >is_number_integer</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a signed integer number</li> <li><a href=../../../features/types/number_handling/ >Number Handling</a> - the article on number handling</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 15:53:29 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320hLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../number_unsigned_t/ >number_unsigned_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> unsigned integer numbers</li> <li><a href=../number_float_t/ >number_float_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> floating-point numbers</li> <li><a href=../is_number_integer/ >is_number_integer</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a signed integer number</li> <li><a href=../../../features/types/number_handling/ >Number Handling</a> - the article on number handling</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 32Line truncated
|
||||
@@ -22,7 +22,7 @@ To store integer numbers in C++, a type is defined by the template parameter `Nu
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `NumberIntegerType` (`std::int64_t`), the default value for `number_integer_t` is `std::int64_t`.
|
||||
With the default values for `NumberIntegerType` (`std::int64_t`), the default type for `number_integer_t` is `std::int64_t`.
|
||||
|
||||
### Default behavior
|
||||
|
||||
|
||||
@@ -32,7 +32,7 @@ the type to use.
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `NumberUnsignedType` (`std::uint64_t`), the default value for `number_unsigned_t` is
|
||||
With the default values for `NumberUnsignedType` (`std::uint64_t`), the default type for `number_unsigned_t` is
|
||||
`#!cpp std::uint64_t`.
|
||||
|
||||
### Default behavior
|
||||
|
||||
@@ -1,5 +1,5 @@
|
||||
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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> numbers (unsigned).</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and <abbr title="Not a Number">NaN</abbr>) are not permitted.</p> </blockquote> <p>This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer, or a floating-point number. Therefore, three different types, <a href=../number_integer_t/ ><code>number_integer_t</code></a>, <code>number_unsigned_t</code> and <a href=../number_float_t/ ><code>number_float_t</code></a> are used.</p> <p>To store unsigned integer numbers in C++, a type is defined by the template parameter <code>NumberUnsignedType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>NumberUnsignedType</code></dt> <dd>the type to store unsigned integers. It must be an <strong>unsigned integral</strong> type (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_integral</span></code>) with a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>numeric_limits</span></code> specialization, and it must be able to represent the absolute value of every <a href=../number_integer_t/ ><code>number_integer_t</code></a> value. See <a href=../../../features/types/template_parameters/#numberintegertype-and-numberunsignedtype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>NumberUnsignedType</code> (<code>std::uint64_t</code>), the default value for <code>number_unsigned_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span></code>.</p> <h3 id=default-behavior>Default behavior<a class=headerlink href=#default-behavior title="Permanent link">¶</a></h3> <ul> <li>The restrictions about leading zeros are not enforced in C++. Instead, leading zeros in integer literals lead to an interpretation as an octal number. Internally, the value will be stored as a decimal number. For instance, the C++ integer literal <code>010</code> will be serialized to <code>8</code>. During deserialization, leading zeros yield an error.</li> </ul> <h3 id=limits>Limits<a class=headerlink href=#limits title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the range and precision of numbers.</p> </blockquote> <p>When the default type is used, the maximal integer number that can be stored is <code>18446744073709551615</code> (UINT64_MAX) and the minimal integer number that can be stored is <code>0</code>. Integer numbers that are out of range will yield over/underflow when used in a constructor. During deserialization (from <abbr title="JavaScript Object Notation">JSON</abbr> text or any of the binary formats), too large or small integer numbers will automatically be stored as <a href=../number_integer_t/ ><code>number_integer_t</code></a> or <a href=../number_float_t/ ><code>number_float_t</code></a>.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> further states:</p> <blockquote> <p>Note that when such software is used, numbers that are integers and are in the range [-2<sup>53</sup>+1, 2<sup>53</sup>-1] are interoperable in the sense that implementations will agree exactly on their numeric values.</p> </blockquote> <p>As this range is a subrange (when considered in conjunction with the <code>number_integer_t</code> type) of the exactly supported range [0, UINT64_MAX], this class's integer type is interoperable.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>Integer number values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>number_unsigned_t</codeLine truncated
|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> numbers (unsigned).</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and <abbr title="Not a Number">NaN</abbr>) are not permitted.</p> </blockquote> <p>This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer, or a floating-point number. Therefore, three different types, <a href=../number_integer_t/ ><code>number_integer_t</code></a>, <code>number_unsigned_t</code> and <a href=../number_float_t/ ><code>number_float_t</code></a> are used.</p> <p>To store unsigned integer numbers in C++, a type is defined by the template parameter <code>NumberUnsignedType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>NumberUnsignedType</code></dt> <dd>the type to store unsigned integers. It must be an <strong>unsigned integral</strong> type (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_integral</span></code>) with a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>numeric_limits</span></code> specialization, and it must be able to represent the absolute value of every <a href=../number_integer_t/ ><code>number_integer_t</code></a> value. See <a href=../../../features/types/template_parameters/#numberintegertype-and-numberunsignedtype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>NumberUnsignedType</code> (<code>std::uint64_t</code>), the default type for <code>number_unsigned_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span></code>.</p> <h3 id=default-behavior>Default behavior<a class=headerlink href=#default-behavior title="Permanent link">¶</a></h3> <ul> <li>The restrictions about leading zeros are not enforced in C++. Instead, leading zeros in integer literals lead to an interpretation as an octal number. Internally, the value will be stored as a decimal number. For instance, the C++ integer literal <code>010</code> will be serialized to <code>8</code>. During deserialization, leading zeros yield an error.</li> </ul> <h3 id=limits>Limits<a class=headerlink href=#limits title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the range and precision of numbers.</p> </blockquote> <p>When the default type is used, the maximal integer number that can be stored is <code>18446744073709551615</code> (UINT64_MAX) and the minimal integer number that can be stored is <code>0</code>. Integer numbers that are out of range will yield over/underflow when used in a constructor. During deserialization (from <abbr title="JavaScript Object Notation">JSON</abbr> text or any of the binary formats), too large or small integer numbers will automatically be stored as <a href=../number_integer_t/ ><code>number_integer_t</code></a> or <a href=../number_float_t/ ><code>number_float_t</code></a>.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> further states:</p> <blockquote> <p>Note that when such software is used, numbers that are integers and are in the range [-2<sup>53</sup>+1, 2<sup>53</sup>-1] are interoperable in the sense that implementations will agree exactly on their numeric values.</p> </blockquote> <p>As this range is a subrange (when considered in conjunction with the <code>number_integer_t</code> type) of the exactly supported range [0, UINT64_MAX], this class's integer type is interoperable.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>Integer number values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>number_unsigned_t</code>Line truncated
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<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
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@@ -10,4 +10,4 @@
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<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><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o><</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=n>json</span><span class=o>::</span><span class=n>number_unsigned_t</span><span class=o>>::</span><span class=n>value</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
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||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
|
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../number_integer_t/ >number_integer_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> integer numbers</li> <li><a href=../number_float_t/ >number_float_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> floating-point numbers</li> <li><a href=../is_number_unsigned/ >is_number_unsigned</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is an unsigned integer number</li> <li><a href=../../../features/types/number_handling/ >Number Handling</a> - the article on number handling</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 15:53:29 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4VLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../number_integer_t/ >number_integer_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> integer numbers</li> <li><a href=../number_float_t/ >number_float_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> floating-point numbers</li> <li><a href=../is_number_unsigned/ >is_number_unsigned</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is an unsigned integer number</li> <li><a href=../../../features/types/number_handling/ >Number Handling</a> - the article on number handling</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.Line truncated
|
||||
@@ -22,7 +22,7 @@ To store unsigned integer numbers in C++, a type is defined by the template para
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `NumberUnsignedType` (`std::uint64_t`), the default value for `number_unsigned_t` is `std::uint64_t`.
|
||||
With the default values for `NumberUnsignedType` (`std::uint64_t`), the default type for `number_unsigned_t` is `std::uint64_t`.
|
||||
|
||||
### Default behavior
|
||||
|
||||
|
||||
@@ -36,7 +36,7 @@ To store objects in C++, a type is defined by the template parameters described
|
||||
### Default type
|
||||
|
||||
With the default values for `ObjectType` (`std::map`), `StringType` (`std::string`), and `AllocatorType`
|
||||
(`std::allocator`), the default value for `object_t` is:
|
||||
(`std::allocator`), the default type for `object_t` is:
|
||||
|
||||
```cpp
|
||||
// until C++14
|
||||
|
||||
@@ -2,7 +2,7 @@
|
||||
<span class=w> </span><span class=n>basic_json</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=n>default_object_comparator_t</span><span class=p>,</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><span class=w> </span><span class=n>basic_json</span><span class=o>>>></span><span class=p>;</span>
|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> objects as follows:</p> <blockquote> <p>An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.</p> </blockquote> <p>To store objects in C++, a type is defined by the template parameters described below.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ObjectType</code></dt> <dd>the container to store objects. Its template parameters must have the same order and meaning as those of <code>std::map</code>; in particular, the third parameter is a comparator. <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>unordered_map</span></code>, whose third parameter is a hash function, therefore needs an adapter -- see <a href=../../../features/types/template_parameters/#objecttype>Template Parameter Requirements</a> for the full list of requirements, an adapter example, and the containers that are known to work.</dd> <dt><code>StringType</code></dt> <dd>the type of the keys or names (e.g., <code>std::string</code>). The comparison function <code>std::less<StringType></code> is used to order elements inside the container.</dd> <dt><code>AllocatorType</code></dt> <dd>the allocator to use for objects (e.g., <code>std::allocator</code>)</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>ObjectType</code> (<code>std::map</code>), <code>StringType</code> (<code>std::string</code>), and <code>AllocatorType</code> (<code>std::allocator</code>), the default value for <code>object_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=c1>// until C++14</span>
|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> objects as follows:</p> <blockquote> <p>An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.</p> </blockquote> <p>To store objects in C++, a type is defined by the template parameters described below.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ObjectType</code></dt> <dd>the container to store objects. Its template parameters must have the same order and meaning as those of <code>std::map</code>; in particular, the third parameter is a comparator. <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>unordered_map</span></code>, whose third parameter is a hash function, therefore needs an adapter -- see <a href=../../../features/types/template_parameters/#objecttype>Template Parameter Requirements</a> for the full list of requirements, an adapter example, and the containers that are known to work.</dd> <dt><code>StringType</code></dt> <dd>the type of the keys or names (e.g., <code>std::string</code>). The comparison function <code>std::less<StringType></code> is used to order elements inside the container.</dd> <dt><code>AllocatorType</code></dt> <dd>the allocator to use for objects (e.g., <code>std::allocator</code>)</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>ObjectType</code> (<code>std::map</code>), <code>StringType</code> (<code>std::string</code>), and <code>AllocatorType</code> (<code>std::allocator</code>), the default type for <code>object_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=c1>// until C++14</span>
|
||||
<span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o><</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=c1>// key_type</span>
|
||||
<span class=w> </span><span class=n>basic_json</span><span class=p>,</span><span class=w> </span><span class=c1>// value_type</span>
|
||||
@@ -28,4 +28,4 @@
|
||||
<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><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=n>map</span><span class=o><</span><span class=n>json</span><span class=o>::</span><span class=n>string_t</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>></span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>object_t</span><span class=o>>::</span><span class=n>value</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../array_t/ >array_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> arrays</li> <li><a href=../string_t/ >string_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> strings</li> <li><a href=../object_comparator_t/ >object_comparator_t</a> the comparator used to order object keys</li> <li><a href=../../../features/object_order/ >Object Order</a> - the article on object key ordering</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Allowed object types whose <code>erase(iterator)</code> returns <code class=highlight><span class=kt>void</span></code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:24:31 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14Line truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../array_t/ >array_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> arrays</li> <li><a href=../string_t/ >string_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> strings</li> <li><a href=../object_comparator_t/ >object_comparator_t</a> the comparator used to order object keys</li> <li><a href=../../../features/object_order/ >Object Order</a> - the article on object key ordering</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Allowed object types whose <code>erase(iterator)</code> returns <code class=highlight><span class=kt>void</span></code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14Line truncated
|
||||
@@ -27,7 +27,7 @@ To store objects in C++, a type is defined by the template parameters described
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `ObjectType` (`std::map`), `StringType` (`std::string`), and `AllocatorType` (`std::allocator`), the default value for `object_t` is:
|
||||
With the default values for `ObjectType` (`std::map`), `StringType` (`std::string`), and `AllocatorType` (`std::allocator`), the default type for `object_t` is:
|
||||
|
||||
```
|
||||
// until C++14
|
||||
|
||||
@@ -20,7 +20,8 @@ bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
|
||||
1. Compares two JSON values for equality according to the following rules:
|
||||
- Two JSON values are equal if (1) neither value is discarded, and (2) they are of the same type and their stored
|
||||
values are the same according to their respective `operator==`.
|
||||
- Integer and floating-point numbers are automatically converted before comparison.
|
||||
- Integer and floating-point numbers are compared by their exact values, without converting the integer to
|
||||
floating-point. For instance, `9007199254740993` and `9007199254740992.0` are not equal.
|
||||
|
||||
2. Compares a JSON value and a scalar or a scalar and a JSON value for equality by converting the
|
||||
scalar to a JSON value and comparing both JSON values according to 1.
|
||||
|
||||
@@ -12,7 +12,7 @@
|
||||
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>ScalarType</span><span class=o>></span>
|
||||
<span class=kt>bool</span><span class=w> </span><span class=k>operator</span><span class=o>==</span><span class=p>(</span><span class=n>ScalarType</span><span class=w> </span><span class=n>rhs</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=cm>/* see below */</span><span class=p>);</span><span class=w> </span><span class=c1>// (2)</span>
|
||||
</code></pre></div> <ol> <li> <p>Compares two <abbr title="JavaScript Object Notation">JSON</abbr> values for equality according to the following rules:</p> <ul> <li>Two <abbr title="JavaScript Object Notation">JSON</abbr> values are equal if (1) neither value is discarded, and (2) they are of the same type and their stored values are the same according to their respective <code>operator==</code>.</li> <li>Integer and floating-point numbers are automatically converted before comparison.</li> </ul> </li> <li> <p>Compares a <abbr title="JavaScript Object Notation">JSON</abbr> value and a scalar or a scalar and a <abbr title="JavaScript Object Notation">JSON</abbr> value for equality by converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value and comparing both <abbr title="JavaScript Object Notation">JSON</abbr> values according to 1.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ScalarType</code></dt> <dd>a scalar type according to <code>std::is_scalar<ScalarType>::value</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>lhs</code> (in)</dt> <dd>first value to consider </dd> <dt><code>rhs</code> (in)</dt> <dd>second value to consider </dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>whether the values <code>lhs</code>/<code>*this</code> and <code>rhs</code> are equal</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <ol> <li>No-throw guarantee: this function never throws exceptions.</li> <li>No-throw guarantee if converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value cannot throw, as for numbers, Booleans, and <code class=highlight><span class=nb>nullptr</span></code>; the function is <code class=highlight><span class=k>noexcept</span></code> exactly in that case. Otherwise, it throws what the conversion throws, for example <code>std::bad_alloc</code> when converting a string, or <a href=../../../home/exceptions/#jsonexceptionout_of_range410><code>out_of_range.410</code></a> for an enum value not mapped by <a href=../../macros/nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a>.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition note"> <p class=admonition-title>Comparing special values</p> <ul> <li><code>NaN</code> values are unordered within the domain of numbers. The following comparisons all yield <code class=highlight><span class=nb>false</span></code>:<ol> <li>Comparing a <code>NaN</code> with itself.</li> <li>Comparing a <code>NaN</code> with another <code>NaN</code>.</li> <li>Comparing a <code>NaN</code> and any other number.</li> </ol> </li> <li><abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=n>null</span></code> values are all equal.</li> <li>Discarded values never compare equal to themselves.</li> </ul> </div> <div class="admonition note"> <p class=admonition-title>Comparing floating-point numbers</p> <p>Floating-point numbers inside <abbr title="JavaScript Object Notation">JSON</abbr> values numbers are compared with <code>json::number_float_t::operator==</code> which is <code>double::operator==</code> by default. To compare floating-point while respecting an epsilon, an alternative <a href="https://github.com/mariokonrad/marnav/blob/master/include/marnav/math/floatingpoint.hpp#L34-#L39">comparison function</a> could be used, for instance</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>std</span><span class=o>::</span><span class=n>enable_if</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=n>is_floating_point</span><span class=o><</span><span class=n>T</span><span class=o>>::</span><span class=n>value</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=o>>::</span><span class=n>type</span><span class=o>></span>
|
||||
</code></pre></div> <ol> <li> <p>Compares two <abbr title="JavaScript Object Notation">JSON</abbr> values for equality according to the following rules:</p> <ul> <li>Two <abbr title="JavaScript Object Notation">JSON</abbr> values are equal if (1) neither value is discarded, and (2) they are of the same type and their stored values are the same according to their respective <code>operator==</code>.</li> <li>Integer and floating-point numbers are compared by their exact values, without converting the integer to floating-point. For instance, <code>9007199254740993</code> and <code>9007199254740992.0</code> are not equal.</li> </ul> </li> <li> <p>Compares a <abbr title="JavaScript Object Notation">JSON</abbr> value and a scalar or a scalar and a <abbr title="JavaScript Object Notation">JSON</abbr> value for equality by converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value and comparing both <abbr title="JavaScript Object Notation">JSON</abbr> values according to 1.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ScalarType</code></dt> <dd>a scalar type according to <code>std::is_scalar<ScalarType>::value</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>lhs</code> (in)</dt> <dd>first value to consider </dd> <dt><code>rhs</code> (in)</dt> <dd>second value to consider </dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>whether the values <code>lhs</code>/<code>*this</code> and <code>rhs</code> are equal</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <ol> <li>No-throw guarantee: this function never throws exceptions.</li> <li>No-throw guarantee if converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value cannot throw, as for numbers, Booleans, and <code class=highlight><span class=nb>nullptr</span></code>; the function is <code class=highlight><span class=k>noexcept</span></code> exactly in that case. Otherwise, it throws what the conversion throws, for example <code>std::bad_alloc</code> when converting a string, or <a href=../../../home/exceptions/#jsonexceptionout_of_range410><code>out_of_range.410</code></a> for an enum value not mapped by <a href=../../macros/nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a>.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition note"> <p class=admonition-title>Comparing special values</p> <ul> <li><code>NaN</code> values are unordered within the domain of numbers. The following comparisons all yield <code class=highlight><span class=nb>false</span></code>:<ol> <li>Comparing a <code>NaN</code> with itself.</li> <li>Comparing a <code>NaN</code> with another <code>NaN</code>.</li> <li>Comparing a <code>NaN</code> and any other number.</li> </ol> </li> <li><abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=n>null</span></code> values are all equal.</li> <li>Discarded values never compare equal to themselves.</li> </ul> </div> <div class="admonition note"> <p class=admonition-title>Comparing floating-point numbers</p> <p>Floating-point numbers inside <abbr title="JavaScript Object Notation">JSON</abbr> values numbers are compared with <code>json::number_float_t::operator==</code> which is <code>double::operator==</code> by default. To compare floating-point while respecting an epsilon, an alternative <a href="https://github.com/mariokonrad/marnav/blob/master/include/marnav/math/floatingpoint.hpp#L34-#L39">comparison function</a> could be used, for instance</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>std</span><span class=o>::</span><span class=n>enable_if</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=n>is_floating_point</span><span class=o><</span><span class=n>T</span><span class=o>>::</span><span class=n>value</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=o>>::</span><span class=n>type</span><span class=o>></span>
|
||||
<span class=kr>inline</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>is_same</span><span class=p>(</span><span class=n>T</span><span class=w> </span><span class=n>a</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=w> </span><span class=n>b</span><span class=p>,</span><span class=w> </span><span class=n>T</span><span class=w> </span><span class=n>epsilon</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>numeric_limits</span><span class=o><</span><span class=n>T</span><span class=o>>::</span><span class=n>epsilon</span><span class=p>())</span><span class=w> </span><span class=k>noexcept</span>
|
||||
<span class=p>{</span>
|
||||
<span class=w> </span><span class=k>return</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>abs</span><span class=p>(</span><span class=n>a</span><span class=w> </span><span class=o>-</span><span class=w> </span><span class=n>b</span><span class=p>)</span><span class=w> </span><span class=o><=</span><span class=w> </span><span class=n>epsilon</span><span class=p>;</span>
|
||||
@@ -113,4 +113,4 @@
|
||||
<span class=mi>17</span><span class=w> </span><span class=err>==</span><span class=w> </span><span class=kc>null</span><span class=err>p</span><span class=kc>tr</span><span class=w> </span><span class=kc>false</span>
|
||||
<span class=s2>"foo"</span><span class=w> </span><span class=err>==</span><span class=w> </span><span class=kc>null</span><span class=err>p</span><span class=kc>tr</span><span class=w> </span><span class=kc>false</span>
|
||||
<span class=kc>null</span><span class=w> </span><span class=err>==</span><span class=w> </span><span class=kc>null</span><span class=err>p</span><span class=kc>tr</span><span class=w> </span><span class=kc>true</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../operator_ne/ >operator!=</a> compare for inequality</li> <li><a href=../operator_spaceship/ >operator<=></a> comparison: 3-way (C++20)</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 1.0.0. Added C++20 member functions in version 3.11.0.</li> <li>Added in version 1.0.0. Added C++20 member functions in version 3.11.0. Made conditionally <code class=highlight><span class=k>noexcept</span></code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; before, a throwing conversion called <code>std::terminate</code>.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 13, 2026 18:06:14 UTC">October 13, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.Line truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../operator_ne/ >operator!=</a> compare for inequality</li> <li><a href=../operator_spaceship/ >operator<=></a> comparison: 3-way (C++20)</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 1.0.0. Added C++20 member functions in version 3.11.0.</li> <li>Added in version 1.0.0. Added C++20 member functions in version 3.11.0. Made conditionally <code class=highlight><span class=k>noexcept</span></code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; before, a throwing conversion called <code>std::terminate</code>.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 15:40:55 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.Line truncated
|
||||
@@ -20,7 +20,7 @@ bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
|
||||
1. Compares two JSON values for equality according to the following rules:
|
||||
|
||||
- Two JSON values are equal if (1) neither value is discarded, and (2) they are of the same type and their stored values are the same according to their respective `operator==`.
|
||||
- Integer and floating-point numbers are automatically converted before comparison.
|
||||
- Integer and floating-point numbers are compared by their exact values, without converting the integer to floating-point. For instance, `9007199254740993` and `9007199254740992.0` are not equal.
|
||||
|
||||
1. Compares a JSON value and a scalar or a scalar and a JSON value for equality by converting the scalar to a JSON value and comparing both JSON values according to 1.
|
||||
|
||||
|
||||
@@ -15,7 +15,8 @@ bool operator<(ScalarType lhs, const const_reference rhs) noexcept(/* see below
|
||||
following rules:
|
||||
- If either operand is discarded, the comparison yields `#!cpp false`.
|
||||
- If both operands have the same type, the values are compared using their respective `operator<`.
|
||||
- Integer and floating-point numbers are automatically converted before comparison.
|
||||
- Integer and floating-point numbers are compared by their exact values, without converting the integer to
|
||||
floating-point. For instance, `9007199254740992.0` is less than `9007199254740993`.
|
||||
- In case `lhs` and `rhs` have different types, the values are ignored and the order of the types
|
||||
is considered, which is:
|
||||
1. null
|
||||
|
||||
@@ -6,7 +6,7 @@
|
||||
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>ScalarType</span><span class=o>></span>
|
||||
<span class=kt>bool</span><span class=w> </span><span class=k>operator</span><span class=o><</span><span class=p>(</span><span class=n>ScalarType</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>const_reference</span><span class=w> </span><span class=n>rhs</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=cm>/* see below */</span><span class=p>);</span><span class=w> </span><span class=c1>// (2)</span>
|
||||
</code></pre></div> <ol> <li> <p>Compares whether one <abbr title="JavaScript Object Notation">JSON</abbr> value <code>lhs</code> is less than another <abbr title="JavaScript Object Notation">JSON</abbr> value <code>rhs</code> according to the following rules:</p> <ul> <li>If either operand is discarded, the comparison yields <code class=highlight><span class=nb>false</span></code>.</li> <li>If both operands have the same type, the values are compared using their respective <code>operator<</code>.</li> <li>Integer and floating-point numbers are automatically converted before comparison.</li> <li>In case <code>lhs</code> and <code>rhs</code> have different types, the values are ignored and the order of the types is considered, which is:<ol> <li>null</li> <li>boolean</li> <li>number (all types)</li> <li>object</li> <li>array</li> <li>string</li> <li>binary For instance, any boolean value is considered less than any string.</li> </ol> </li> </ul> </li> <li> <p>Compares whether a <abbr title="JavaScript Object Notation">JSON</abbr> value is less than a scalar or a scalar is less than a <abbr title="JavaScript Object Notation">JSON</abbr> value by converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value and comparing both <abbr title="JavaScript Object Notation">JSON</abbr> values according to 1.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ScalarType</code></dt> <dd>a scalar type according to <code>std::is_scalar<ScalarType>::value</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>lhs</code> (in)</dt> <dd>first value to consider </dd> <dt><code>rhs</code> (in)</dt> <dd>second value to consider </dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>whether <code>lhs</code> is less than <code>rhs</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <ol> <li>No-throw guarantee: this function never throws exceptions.</li> <li>No-throw guarantee if converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value cannot throw, as for numbers, Booleans, and <code class=highlight><span class=nb>nullptr</span></code>; the function is <code class=highlight><span class=k>noexcept</span></code> exactly in that case. Otherwise, it throws what the conversion throws, for example <code>std::bad_alloc</code> when converting a string, or <a href=../../../home/exceptions/#jsonexceptionout_of_range410><code>out_of_range.410</code></a> for an enum value not mapped by <a href=../../macros/nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a>.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition note"> <p class=admonition-title>Comparing <code>NaN</code></p> <p><code>NaN</code> values are unordered within the domain of numbers. The following comparisons all yield <code class=highlight><span class=nb>false</span></code>: 1. Comparing a <code>NaN</code> with itself. 2. Comparing a <code>NaN</code> with another <code>NaN</code>. 3. Comparing a <code>NaN</code> and any other number.</p> </div> <div class="admonition note"> <p class=admonition-title>Operator overload resolution</p> <p>Since C++20 overload resolution will consider the <em>rewritten candidate</em> generated from <a href=../operator_spaceship/ ><code>operator<=></code></a>.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example demonstrates comparing several <abbr title="JavaScript Object Notation">JSON</abbr> types.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
</code></pre></div> <ol> <li> <p>Compares whether one <abbr title="JavaScript Object Notation">JSON</abbr> value <code>lhs</code> is less than another <abbr title="JavaScript Object Notation">JSON</abbr> value <code>rhs</code> according to the following rules:</p> <ul> <li>If either operand is discarded, the comparison yields <code class=highlight><span class=nb>false</span></code>.</li> <li>If both operands have the same type, the values are compared using their respective <code>operator<</code>.</li> <li>Integer and floating-point numbers are compared by their exact values, without converting the integer to floating-point. For instance, <code>9007199254740992.0</code> is less than <code>9007199254740993</code>.</li> <li>In case <code>lhs</code> and <code>rhs</code> have different types, the values are ignored and the order of the types is considered, which is:<ol> <li>null</li> <li>boolean</li> <li>number (all types)</li> <li>object</li> <li>array</li> <li>string</li> <li>binary For instance, any boolean value is considered less than any string.</li> </ol> </li> </ul> </li> <li> <p>Compares whether a <abbr title="JavaScript Object Notation">JSON</abbr> value is less than a scalar or a scalar is less than a <abbr title="JavaScript Object Notation">JSON</abbr> value by converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value and comparing both <abbr title="JavaScript Object Notation">JSON</abbr> values according to 1.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ScalarType</code></dt> <dd>a scalar type according to <code>std::is_scalar<ScalarType>::value</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>lhs</code> (in)</dt> <dd>first value to consider </dd> <dt><code>rhs</code> (in)</dt> <dd>second value to consider </dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>whether <code>lhs</code> is less than <code>rhs</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <ol> <li>No-throw guarantee: this function never throws exceptions.</li> <li>No-throw guarantee if converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value cannot throw, as for numbers, Booleans, and <code class=highlight><span class=nb>nullptr</span></code>; the function is <code class=highlight><span class=k>noexcept</span></code> exactly in that case. Otherwise, it throws what the conversion throws, for example <code>std::bad_alloc</code> when converting a string, or <a href=../../../home/exceptions/#jsonexceptionout_of_range410><code>out_of_range.410</code></a> for an enum value not mapped by <a href=../../macros/nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a>.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition note"> <p class=admonition-title>Comparing <code>NaN</code></p> <p><code>NaN</code> values are unordered within the domain of numbers. The following comparisons all yield <code class=highlight><span class=nb>false</span></code>: 1. Comparing a <code>NaN</code> with itself. 2. Comparing a <code>NaN</code> with another <code>NaN</code>. 3. Comparing a <code>NaN</code> and any other number.</p> </div> <div class="admonition note"> <p class=admonition-title>Operator overload resolution</p> <p>Since C++20 overload resolution will consider the <em>rewritten candidate</em> generated from <a href=../operator_spaceship/ ><code>operator<=></code></a>.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The example demonstrates comparing several <abbr title="JavaScript Object Notation">JSON</abbr> types.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><iostream></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
|
||||
@@ -34,4 +34,4 @@
|
||||
<span class=p>{</span><span class=nt>"A"</span><span class=p>:</span><span class=s2>"a"</span><span class=p>,</span><span class=nt>"B"</span><span class=p>:</span><span class=s2>"b"</span><span class=p>}</span><span class=w> </span><span class=err>==</span><span class=w> </span><span class=p>{</span><span class=nt>"A"</span><span class=p>:</span><span class=s2>"a"</span><span class=p>,</span><span class=nt>"B"</span><span class=p>:</span><span class=s2>"b"</span><span class=p>}</span><span class=w> </span><span class=kc>false</span>
|
||||
<span class=mi>17</span><span class=w> </span><span class=err>==</span><span class=w> </span><span class=mf>17.0000000000001</span><span class=w> </span><span class=kc>true</span>
|
||||
<span class=s2>"foo"</span><span class=w> </span><span class=err>==</span><span class=w> </span><span class=s2>"bar"</span><span class=w> </span><span class=kc>false</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../operator_spaceship/ ><strong>operator<=></strong></a> comparison: 3-way</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.</li> <li>Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0. Made conditionally <code class=highlight><span class=k>noexcept</span></code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; before, a throwing conversion called <code>std::terminate</code>.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 2, 2026 15:25:17 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 - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7v29Line truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../operator_spaceship/ ><strong>operator<=></strong></a> comparison: 3-way</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.</li> <li>Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0. Made conditionally <code class=highlight><span class=k>noexcept</span></code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; before, a throwing conversion called <code>std::terminate</code>.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 15:40:55 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-39.9 54.9V416h-66.4V202.2h63.7vLine truncated
|
||||
@@ -15,7 +15,7 @@ bool operator<(ScalarType lhs, const const_reference rhs) noexcept(/* see below
|
||||
|
||||
- If either operand is discarded, the comparison yields `false`.
|
||||
- If both operands have the same type, the values are compared using their respective `operator<`.
|
||||
- Integer and floating-point numbers are automatically converted before comparison.
|
||||
- Integer and floating-point numbers are compared by their exact values, without converting the integer to floating-point. For instance, `9007199254740992.0` is less than `9007199254740993`.
|
||||
- In case `lhs` and `rhs` have different types, the values are ignored and the order of the types is considered, which is:
|
||||
1. null
|
||||
1. boolean
|
||||
|
||||
@@ -12,10 +12,8 @@ std::partial_ordering operator<=>(const ScalarType rhs) const noexcept(/* see be
|
||||
- Two JSON values compare with a result of `std::partial_ordering::unordered` if either value is discarded.
|
||||
- If both JSON values are of the same type, the result is produced by 3-way comparing their stored values using
|
||||
their respective `operator<=>`.
|
||||
- Integer and floating-point numbers are converted to their common type and then 3-way compared using their
|
||||
respective `operator<=>`.
|
||||
For instance, comparing an integer and a floating-point value will 3-way compare the first value converted to
|
||||
floating-point with the second value.
|
||||
- Integer and floating-point numbers are 3-way compared by their exact values, without converting the integer to
|
||||
floating-point. For instance, `9007199254740993` compares greater than `9007199254740992.0`.
|
||||
- Otherwise, yields a result by comparing the type (see [`value_t`](value_t.md)).
|
||||
|
||||
2. 3-way compares a JSON value and a scalar or a scalar and a JSON value by converting the scalar to a JSON value and
|
||||
|
||||
@@ -3,7 +3,7 @@
|
||||
|
||||
<span class=k>template</span><span class=o><</span><span class=k>typename</span><span class=w> </span><span class=nc>ScalarType</span><span class=o>></span>
|
||||
<span class=n>std</span><span class=o>::</span><span class=n>partial_ordering</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>ScalarType</span><span class=w> </span><span class=n>rhs</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=cm>/* see below */</span><span class=p>);</span><span class=w> </span><span class=c1>// (2)</span>
|
||||
</code></pre></div> <ol> <li> <p>3-way compares two <abbr title="JavaScript Object Notation">JSON</abbr> values producing a result of type <code>std::partial_ordering</code> according to the following rules:</p> <ul> <li>Two <abbr title="JavaScript Object Notation">JSON</abbr> values compare with a result of <code>std::partial_ordering::unordered</code> if either value is discarded.</li> <li>If both <abbr title="JavaScript Object Notation">JSON</abbr> values are of the same type, the result is produced by 3-way comparing their stored values using their respective <code>operator<=></code>.</li> <li>Integer and floating-point numbers are converted to their common type and then 3-way compared using their respective <code>operator<=></code>. For instance, comparing an integer and a floating-point value will 3-way compare the first value converted to floating-point with the second value.</li> <li>Otherwise, yields a result by comparing the type (see <a href=../value_t/ ><code>value_t</code></a>).</li> </ul> </li> <li> <p>3-way compares a <abbr title="JavaScript Object Notation">JSON</abbr> value and a scalar or a scalar and a <abbr title="JavaScript Object Notation">JSON</abbr> value by converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value and 3-way comparing both <abbr title="JavaScript Object Notation">JSON</abbr> values (see 1).</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ScalarType</code></dt> <dd>a scalar type according to <code>std::is_scalar<ScalarType>::value</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>rhs</code> (in)</dt> <dd>second value to consider </dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>the <code>std::partial_ordering</code> of the 3-way comparison of <code>*this</code> and <code>rhs</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <ol> <li>No-throw guarantee: this function never throws exceptions.</li> <li>No-throw guarantee if converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value cannot throw, as for numbers, Booleans, and <code class=highlight><span class=nb>nullptr</span></code>; the function is <code class=highlight><span class=k>noexcept</span></code> exactly in that case. Otherwise, it throws what the conversion throws, for example <code>std::bad_alloc</code> when converting a string, or <a href=../../../home/exceptions/#jsonexceptionout_of_range410><code>out_of_range.410</code></a> for an enum value not mapped by <a href=../../macros/nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a>.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition note"> <p class=admonition-title>Comparing <code>NaN</code></p> <ul> <li><code>NaN</code> values are unordered within the domain of numbers. The following comparisons all yield <code>std::partial_ordering::unordered</code>:<ol> <li>Comparing a <code>NaN</code> with itself.</li> <li>Comparing a <code>NaN</code> with another <code>NaN</code>.</li> <li>Comparing a <code>NaN</code> and any other number.</li> </ol> </li> </ul> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: (1) comparing <abbr title="JavaScript Object Notation">JSON</abbr> values</summary> <p>The example demonstrates comparing several <abbr title="JavaScript Object Notation">JSON</abbr> values.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><compare></span>
|
||||
</code></pre></div> <ol> <li> <p>3-way compares two <abbr title="JavaScript Object Notation">JSON</abbr> values producing a result of type <code>std::partial_ordering</code> according to the following rules:</p> <ul> <li>Two <abbr title="JavaScript Object Notation">JSON</abbr> values compare with a result of <code>std::partial_ordering::unordered</code> if either value is discarded.</li> <li>If both <abbr title="JavaScript Object Notation">JSON</abbr> values are of the same type, the result is produced by 3-way comparing their stored values using their respective <code>operator<=></code>.</li> <li>Integer and floating-point numbers are 3-way compared by their exact values, without converting the integer to floating-point. For instance, <code>9007199254740993</code> compares greater than <code>9007199254740992.0</code>.</li> <li>Otherwise, yields a result by comparing the type (see <a href=../value_t/ ><code>value_t</code></a>).</li> </ul> </li> <li> <p>3-way compares a <abbr title="JavaScript Object Notation">JSON</abbr> value and a scalar or a scalar and a <abbr title="JavaScript Object Notation">JSON</abbr> value by converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value and 3-way comparing both <abbr title="JavaScript Object Notation">JSON</abbr> values (see 1).</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>ScalarType</code></dt> <dd>a scalar type according to <code>std::is_scalar<ScalarType>::value</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>rhs</code> (in)</dt> <dd>second value to consider </dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>the <code>std::partial_ordering</code> of the 3-way comparison of <code>*this</code> and <code>rhs</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <ol> <li>No-throw guarantee: this function never throws exceptions.</li> <li>No-throw guarantee if converting the scalar to a <abbr title="JavaScript Object Notation">JSON</abbr> value cannot throw, as for numbers, Booleans, and <code class=highlight><span class=nb>nullptr</span></code>; the function is <code class=highlight><span class=k>noexcept</span></code> exactly in that case. Otherwise, it throws what the conversion throws, for example <code>std::bad_alloc</code> when converting a string, or <a href=../../../home/exceptions/#jsonexceptionout_of_range410><code>out_of_range.410</code></a> for an enum value not mapped by <a href=../../macros/nlohmann_json_serialize_enum_strict/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM_STRICT</code></a>.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition note"> <p class=admonition-title>Comparing <code>NaN</code></p> <ul> <li><code>NaN</code> values are unordered within the domain of numbers. The following comparisons all yield <code>std::partial_ordering::unordered</code>:<ol> <li>Comparing a <code>NaN</code> with itself.</li> <li>Comparing a <code>NaN</code> with another <code>NaN</code>.</li> <li>Comparing a <code>NaN</code> and any other number.</li> </ol> </li> </ul> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example: (1) comparing <abbr title="JavaScript Object Notation">JSON</abbr> values</summary> <p>The example demonstrates comparing several <abbr title="JavaScript Object Notation">JSON</abbr> values.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf><compare></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><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -91,4 +91,4 @@
|
||||
<span class=mi>17</span><span class=w> </span><span class=err><=></span><span class=w> </span><span class=mf>17.000000</span><span class=w> </span><span class=p>:</span><span class=err>=</span><span class=w> </span><span class=err>equivale</span><span class=kc>nt</span>
|
||||
<span class=mi>17</span><span class=w> </span><span class=err><=></span><span class=w> </span><span class=kc>nan</span><span class=w> </span><span class=p>:</span><span class=err>=</span><span class=w> </span><span class=err>u</span><span class=kc>n</span><span class=err>ordered</span>
|
||||
<span class=s2>"17"</span><span class=w> </span><span class=err><=></span><span class=w> </span><span class=mi>17</span><span class=w> </span><span class=p>:</span><span class=err>=</span><span class=w> </span><span class=err>grea</span><span class=kc>ter</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../operator_eq/ ><strong>operator==</strong></a> - comparison: equal</li> <li><a href=../operator_ne/ ><strong>operator!=</strong></a> - comparison: not equal</li> <li><a href=../operator_lt/ ><strong>operator<</strong></a> - comparison: less than</li> <li><a href=../operator_le/ ><strong>operator<=</strong></a> - comparison: less than or equal</li> <li><a href=../operator_gt/ ><strong>operator></strong></a> - comparison: greater than</li> <li><a href=../operator_ge/ ><strong>operator>=</strong></a> - comparison: greater than or equal</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.0. Made conditionally <code class=highlight><span class=k>noexcept</span></code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; before, a throwing conversion called <code>std::terminate</code>.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 13, 2026 18:06:14 UTC">October 13, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SLine truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../operator_eq/ ><strong>operator==</strong></a> - comparison: equal</li> <li><a href=../operator_ne/ ><strong>operator!=</strong></a> - comparison: not equal</li> <li><a href=../operator_lt/ ><strong>operator<</strong></a> - comparison: less than</li> <li><a href=../operator_le/ ><strong>operator<=</strong></a> - comparison: less than or equal</li> <li><a href=../operator_gt/ ><strong>operator></strong></a> - comparison: greater than</li> <li><a href=../operator_ge/ ><strong>operator>=</strong></a> - comparison: greater than or equal</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 3.11.0. Made conditionally <code class=highlight><span class=k>noexcept</span></code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; before, a throwing conversion called <code>std::terminate</code>.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 15:40:55 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SLine truncated
|
||||
@@ -12,7 +12,7 @@ std::partial_ordering operator<=>(const ScalarType rhs) const noexcept(/* see be
|
||||
|
||||
- Two JSON values compare with a result of `std::partial_ordering::unordered` if either value is discarded.
|
||||
- If both JSON values are of the same type, the result is produced by 3-way comparing their stored values using their respective `operator<=>`.
|
||||
- Integer and floating-point numbers are converted to their common type and then 3-way compared using their respective `operator<=>`. For instance, comparing an integer and a floating-point value will 3-way compare the first value converted to floating-point with the second value.
|
||||
- Integer and floating-point numbers are 3-way compared by their exact values, without converting the integer to floating-point. For instance, `9007199254740993` compares greater than `9007199254740992.0`.
|
||||
- Otherwise, yields a result by comparing the type (see [`value_t`](https://json.nlohmann.me/api/basic_json/value_t/index.md)).
|
||||
|
||||
1. 3-way compares a JSON value and a scalar or a scalar and a JSON value by converting the scalar to a JSON value and 3-way comparing both JSON values (see 1).
|
||||
|
||||
@@ -45,7 +45,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
|
||||
pointer inside the patch cannot be resolved, e.g., `-` in a "remove" operation or `1a` for an array; example:
|
||||
`"unresolved reference token '-'"`.
|
||||
- Throws [`out_of_range.405`](../../home/exceptions.md#jsonexceptionout_of_range405) if JSON pointer has no parent
|
||||
("add", "remove", "move")
|
||||
("remove", "move")
|
||||
- Throws [`out_of_range.411`](../../home/exceptions.md#jsonexceptionout_of_range411) if an "add" operation's target
|
||||
location has a parent that is neither an object nor an array.
|
||||
- Throws [`out_of_range.413`](../../home/exceptions.md#jsonexceptionout_of_range413) if a "remove" operation's target
|
||||
|
||||
@@ -1,5 +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/patch/" rel="canonical"><link href=../parser_callback_t/ rel=prev><link href=../patch_inplace/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>patch - 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><a href="http://jsonpatch.com"><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a> defines a <abbr title="JavaScript Object Notation">JSON</abbr> document structure for expressing a sequence of operations to apply to a <abbr title="JavaScript Object Notation">JSON</abbr> document. With this function, a <abbr title="JavaScript Object Notation">JSON</abbr> Patch is applied to the current <abbr title="JavaScript Object Notation">JSON</abbr> value by executing all operations from the patch.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>json_patch</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> patch document</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>patched document</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error104><code>parse_error.104</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> patch does not consist of an array of objects.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error105><code>parse_error.105</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> patch is malformed (e.g., mandatory attributes are missing); example: <code>"operation 'add' must have member 'path'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if an array index is out of range.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error106><code>parse_error.106</code></a> if an array index in a "path" or "from" member begins with '0'; example: <code>"array index '01' must not begin with '0'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error107><code>parse_error.107</code></a> if a "path" or "from" member is not empty and does not begin with a slash (<code>/</code>); example: <code>"JSON pointer must be empty or begin with '/' - was: 'a'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error108><code>parse_error.108</code></a> if a tilde (<code>~</code>) in a "path" or "from" member is not followed by <code>0</code> or <code>1</code>; example: <code>"escape character '~' must be followed with '0' or '1'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> if an array index in a "path" or "from" member is not a number; example: <code>"array index 'foo' is not a number"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range402><code>out_of_range.402</code></a> if the array index <code>-</code> is used where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example: <code>"array index '-' (3) is out of range"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if a <abbr title="JavaScript Object Notation">JSON</abbr> pointer inside the patch could not be resolved successfully in the current <abbr title="JavaScript Object Notation">JSON</abbr> value; example: <code>"key baz not found"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> if a reference token of a <abbr title="JavaScript Object Notation">JSON</abbr> pointer inside the patch cannot be resolved, e.g., <code>-</code> in a "remove" operation or <code>1a</code> for an array; example: <code>"unresolved reference token '-'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range405><code>out_of_range.405</code></a> if <abbr title="JavaScript Object Notation">JSON</abbr> pointer has no parent ("add", "remove", "move")</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range411><code>out_of_range.411</code></a> if an "add" operation's target location has a parent that is neither an object nor an array.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range413><code>out_of_range.413</code></a> if a "remove" operation's target location has a parent that is neither an object nor an array.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range414><code>out_of_range.414</code></a> if a "move" operation's "from" location is a proper prefix of its "path" location.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionother_error501><code>other_error.501</code></a> if "test" operation was unsuccessful.</li> </Line truncated
|
||||
</code></pre></div> <p><a href="http://jsonpatch.com"><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a> defines a <abbr title="JavaScript Object Notation">JSON</abbr> document structure for expressing a sequence of operations to apply to a <abbr title="JavaScript Object Notation">JSON</abbr> document. With this function, a <abbr title="JavaScript Object Notation">JSON</abbr> Patch is applied to the current <abbr title="JavaScript Object Notation">JSON</abbr> value by executing all operations from the patch.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>json_patch</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> patch document</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>patched document</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error104><code>parse_error.104</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> patch does not consist of an array of objects.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error105><code>parse_error.105</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> patch is malformed (e.g., mandatory attributes are missing); example: <code>"operation 'add' must have member 'path'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if an array index is out of range.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error106><code>parse_error.106</code></a> if an array index in a "path" or "from" member begins with '0'; example: <code>"array index '01' must not begin with '0'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error107><code>parse_error.107</code></a> if a "path" or "from" member is not empty and does not begin with a slash (<code>/</code>); example: <code>"JSON pointer must be empty or begin with '/' - was: 'a'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error108><code>parse_error.108</code></a> if a tilde (<code>~</code>) in a "path" or "from" member is not followed by <code>0</code> or <code>1</code>; example: <code>"escape character '~' must be followed with '0' or '1'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> if an array index in a "path" or "from" member is not a number; example: <code>"array index 'foo' is not a number"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range402><code>out_of_range.402</code></a> if the array index <code>-</code> is used where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example: <code>"array index '-' (3) is out of range"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if a <abbr title="JavaScript Object Notation">JSON</abbr> pointer inside the patch could not be resolved successfully in the current <abbr title="JavaScript Object Notation">JSON</abbr> value; example: <code>"key baz not found"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> if a reference token of a <abbr title="JavaScript Object Notation">JSON</abbr> pointer inside the patch cannot be resolved, e.g., <code>-</code> in a "remove" operation or <code>1a</code> for an array; example: <code>"unresolved reference token '-'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range405><code>out_of_range.405</code></a> if <abbr title="JavaScript Object Notation">JSON</abbr> pointer has no parent ("remove", "move")</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range411><code>out_of_range.411</code></a> if an "add" operation's target location has a parent that is neither an object nor an array.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range413><code>out_of_range.413</code></a> if a "remove" operation's target location has a parent that is neither an object nor an array.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range414><code>out_of_range.414</code></a> if a "move" operation's "from" location is a proper prefix of its "path" location.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionother_error501><code>other_error.501</code></a> if "test" operation was unsuccessful.</li> </ul> <h2Line truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -85,4 +85,4 @@
|
||||
<span class=w> </span><span class=nt>"b"</span><span class=p>:</span><span class=w> </span><span class=mi>1</span>
|
||||
<span class=w> </span><span class=p>}</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a></li> <li><a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901 (<abbr title="JavaScript Object Notation">JSON</abbr> Pointer)</a></li> <li><a href=../patch_inplace/ >patch_inplace</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch without creating a copy of the document</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.0.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range411><code>out_of_range.411</code></a> and stopped relying on an internal assertion when an "add" operation's target location has a non-object/non-array parent in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range413><code>out_of_range.413</code></a> and stopped silently ignoring a "remove" operation whose target location has a non-object/non-array parent in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range414><code>out_of_range.414</code></a> and rejected a "move" operation whose "from" location is a proper prefix of its "path" location instead of silently producing a corrupted result in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> instead of <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> for a one-character array index that is not a digit (e.g., <code>/x</code>) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, as it already did for longer ones.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:41 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69Line truncated
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a></li> <li><a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901 (<abbr title="JavaScript Object Notation">JSON</abbr> Pointer)</a></li> <li><a href=../patch_inplace/ >patch_inplace</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch without creating a copy of the document</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 2.0.0.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range411><code>out_of_range.411</code></a> and stopped relying on an internal assertion when an "add" operation's target location has a non-object/non-array parent in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range413><code>out_of_range.413</code></a> and stopped silently ignoring a "remove" operation whose target location has a non-object/non-array parent in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range414><code>out_of_range.414</code></a> and rejected a "move" operation whose "from" location is a proper prefix of its "path" location instead of silently producing a corrupted result in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> instead of <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> for a one-character array index that is not a digit (e.g., <code>/x</code>) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, as it already did for longer ones.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 15:40:55 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69Line truncated
|
||||
@@ -30,7 +30,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
|
||||
- Throws [`out_of_range.402`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range402) if the array index `-` is used where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example: `"array index '-' (3) is out of range"`.
|
||||
- Throws [`out_of_range.403`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range403) if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example: `"key baz not found"`.
|
||||
- Throws [`out_of_range.404`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range404) if a reference token of a JSON pointer inside the patch cannot be resolved, e.g., `-` in a "remove" operation or `1a` for an array; example: `"unresolved reference token '-'"`.
|
||||
- Throws [`out_of_range.405`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range405) if JSON pointer has no parent ("add", "remove", "move")
|
||||
- Throws [`out_of_range.405`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range405) if JSON pointer has no parent ("remove", "move")
|
||||
- Throws [`out_of_range.411`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range411) if an "add" operation's target location has a parent that is neither an object nor an array.
|
||||
- Throws [`out_of_range.413`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range413) if a "remove" operation's target location has a parent that is neither an object nor an array.
|
||||
- Throws [`out_of_range.414`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range414) if a "move" operation's "from" location is a proper prefix of its "path" location.
|
||||
|
||||
@@ -41,7 +41,7 @@ No guarantees, value may be corrupted by an unsuccessful patch operation.
|
||||
pointer inside the patch cannot be resolved, e.g., `-` in a "remove" operation or `1a` for an array; example:
|
||||
`"unresolved reference token '-'"`.
|
||||
- Throws [`out_of_range.405`](../../home/exceptions.md#jsonexceptionout_of_range405) if JSON pointer has no parent
|
||||
("add", "remove", "move")
|
||||
("remove", "move")
|
||||
- Throws [`out_of_range.411`](../../home/exceptions.md#jsonexceptionout_of_range411) if an "add" operation's target
|
||||
location has a parent that is neither an object nor an array.
|
||||
- Throws [`out_of_range.413`](../../home/exceptions.md#jsonexceptionout_of_range413) if a "remove" operation's target
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||||
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||||
@@ -1,5 +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/patch_inplace/" rel="canonical"><link href=../patch/ rel=prev><link href=../push_back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>patch_inplace - 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> patch_inplace </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 Line truncated
|
||||
</code></pre></div> <p><a href="http://jsonpatch.com"><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a> defines a <abbr title="JavaScript Object Notation">JSON</abbr> document structure for expressing a sequence of operations to apply to a <abbr title="JavaScript Object Notation">JSON</abbr> document. With this function, a <abbr title="JavaScript Object Notation">JSON</abbr> Patch is applied to the current <abbr title="JavaScript Object Notation">JSON</abbr> value by executing all operations from the patch. This function applies a <abbr title="JavaScript Object Notation">JSON</abbr> patch in place and returns void.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>json_patch</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> patch document</dd> </dl> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No guarantees, value may be corrupted by an unsuccessful patch operation.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error104><code>parse_error.104</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> patch does not consist of an array of objects.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error105><code>parse_error.105</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> patch is malformed (e.g., mandatory attributes are missing); example: <code>"operation 'add' must have member 'path'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if an array index is out of range.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error106><code>parse_error.106</code></a> if an array index in a "path" or "from" member begins with '0'; example: <code>"array index '01' must not begin with '0'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error107><code>parse_error.107</code></a> if a "path" or "from" member is not empty and does not begin with a slash (<code>/</code>); example: <code>"JSON pointer must be empty or begin with '/' - was: 'a'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error108><code>parse_error.108</code></a> if a tilde (<code>~</code>) in a "path" or "from" member is not followed by <code>0</code> or <code>1</code>; example: <code>"escape character '~' must be followed with '0' or '1'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> if an array index in a "path" or "from" member is not a number; example: <code>"array index 'foo' is not a number"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range402><code>out_of_range.402</code></a> if the array index <code>-</code> is used where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example: <code>"array index '-' (3) is out of range"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if a <abbr title="JavaScript Object Notation">JSON</abbr> pointer inside the patch could not be resolved successfully in the current <abbr title="JavaScript Object Notation">JSON</abbr> value; example: <code>"key baz not found"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> if a reference token of a <abbr title="JavaScript Object Notation">JSON</abbr> pointer inside the patch cannot be resolved, e.g., <code>-</code> in a "remove" operation or <code>1a</code> for an array; example: <code>"unresolved reference token '-'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range405><code>out_of_range.405</code></a> if <abbr title="JavaScript Object Notation">JSON</abbr> pointer has no parent ("add", "remove", "move")</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range411><code>out_of_range.411</code></a> if an "add" operation's target location has a parent that is neither an object nor an array.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range413><code>out_of_range.413</code></a> if a "remove" operation's target location has a parent that is neither an object nor an array.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range414><code>out_of_range.414</code></a> if a "move" operation's "from" location is a proper prefix of its "path" location.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionother_error501><code>other_error.501</code></a> if "test" operation was unsuccessful.</li> </ul> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="PermaneLine truncated
|
||||
</code></pre></div> <p><a href="http://jsonpatch.com"><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a> defines a <abbr title="JavaScript Object Notation">JSON</abbr> document structure for expressing a sequence of operations to apply to a <abbr title="JavaScript Object Notation">JSON</abbr> document. With this function, a <abbr title="JavaScript Object Notation">JSON</abbr> Patch is applied to the current <abbr title="JavaScript Object Notation">JSON</abbr> value by executing all operations from the patch. This function applies a <abbr title="JavaScript Object Notation">JSON</abbr> patch in place and returns void.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>json_patch</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> patch document</dd> </dl> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>No guarantees, value may be corrupted by an unsuccessful patch operation.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error104><code>parse_error.104</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> patch does not consist of an array of objects.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error105><code>parse_error.105</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> patch is malformed (e.g., mandatory attributes are missing); example: <code>"operation 'add' must have member 'path'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if an array index is out of range.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error106><code>parse_error.106</code></a> if an array index in a "path" or "from" member begins with '0'; example: <code>"array index '01' must not begin with '0'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error107><code>parse_error.107</code></a> if a "path" or "from" member is not empty and does not begin with a slash (<code>/</code>); example: <code>"JSON pointer must be empty or begin with '/' - was: 'a'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error108><code>parse_error.108</code></a> if a tilde (<code>~</code>) in a "path" or "from" member is not followed by <code>0</code> or <code>1</code>; example: <code>"escape character '~' must be followed with '0' or '1'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> if an array index in a "path" or "from" member is not a number; example: <code>"array index 'foo' is not a number"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range402><code>out_of_range.402</code></a> if the array index <code>-</code> is used where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example: <code>"array index '-' (3) is out of range"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if a <abbr title="JavaScript Object Notation">JSON</abbr> pointer inside the patch could not be resolved successfully in the current <abbr title="JavaScript Object Notation">JSON</abbr> value; example: <code>"key baz not found"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> if a reference token of a <abbr title="JavaScript Object Notation">JSON</abbr> pointer inside the patch cannot be resolved, e.g., <code>-</code> in a "remove" operation or <code>1a</code> for an array; example: <code>"unresolved reference token '-'"</code>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range405><code>out_of_range.405</code></a> if <abbr title="JavaScript Object Notation">JSON</abbr> pointer has no parent ("remove", "move")</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range411><code>out_of_range.411</code></a> if an "add" operation's target location has a parent that is neither an object nor an array.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range413><code>out_of_range.413</code></a> if a "remove" operation's target location has a parent that is neither an object nor an array.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range414><code>out_of_range.414</code></a> if a "move" operation's "from" location is a proper prefix of its "path" location.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionother_error501><code>other_error.501</code></a> if "test" operation was unsuccessful.</li> </ul> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent linkLine truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -90,4 +90,4 @@
|
||||
<span class=w> </span><span class=nt>"a"</span><span class=p>:</span><span class=w> </span><span class=mi>99</span><span class=p>,</span>
|
||||
<span class=w> </span><span class=nt>"b"</span><span class=p>:</span><span class=w> </span><span class=mi>2</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a></li> <li><a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901 (<abbr title="JavaScript Object Notation">JSON</abbr> Pointer)</a></li> <li><a href=../patch/ >patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.11.0.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range411><code>out_of_range.411</code></a> and stopped relying on an internal assertion when an "add" operation's target location has a non-object/non-array parent in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range413><code>out_of_range.413</code></a> and stopped silently ignoring a "remove" operation whose target location has a non-object/non-array parent in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range414><code>out_of_range.414</code></a> and rejected a "move" operation whose "from" location is a proper prefix of its "path" location instead of silently producing a corrupted result in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> instead of <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> for a one-character array index that is not a digit (e.g., <code>/x</code>) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, as it already did for longer ones.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 11, 2026 06:21:41 UTC">October 11, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-Line truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a></li> <li><a href="https://tools.ietf.org/html/rfc6901"><abbr title="Request for Comments">RFC</abbr> 6901 (<abbr title="JavaScript Object Notation">JSON</abbr> Pointer)</a></li> <li><a href=../patch/ >patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.11.0.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range411><code>out_of_range.411</code></a> and stopped relying on an internal assertion when an "add" operation's target location has a non-object/non-array parent in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range413><code>out_of_range.413</code></a> and stopped silently ignoring a "remove" operation whose target location has a non-object/non-array parent in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Added <a href=../../../home/exceptions/#jsonexceptionout_of_range414><code>out_of_range.414</code></a> and rejected a "move" operation whose "from" location is a proper prefix of its "path" location instead of silently producing a corrupted result in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> instead of <a href=../../../home/exceptions/#jsonexceptionout_of_range404><code>out_of_range.404</code></a> for a one-character array index that is not a digit (e.g., <code>/x</code>) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, as it already did for longer ones.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 15:40:55 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-Line truncated
|
||||
@@ -26,7 +26,7 @@ No guarantees, value may be corrupted by an unsuccessful patch operation.
|
||||
- Throws [`out_of_range.402`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range402) if the array index `-` is used where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example: `"array index '-' (3) is out of range"`.
|
||||
- Throws [`out_of_range.403`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range403) if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example: `"key baz not found"`.
|
||||
- Throws [`out_of_range.404`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range404) if a reference token of a JSON pointer inside the patch cannot be resolved, e.g., `-` in a "remove" operation or `1a` for an array; example: `"unresolved reference token '-'"`.
|
||||
- Throws [`out_of_range.405`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range405) if JSON pointer has no parent ("add", "remove", "move")
|
||||
- Throws [`out_of_range.405`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range405) if JSON pointer has no parent ("remove", "move")
|
||||
- Throws [`out_of_range.411`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range411) if an "add" operation's target location has a parent that is neither an object nor an array.
|
||||
- Throws [`out_of_range.413`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range413) if a "remove" operation's target location has a parent that is neither an object nor an array.
|
||||
- Throws [`out_of_range.414`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range414) if a "move" operation's "from" location is a proper prefix of its "path" location.
|
||||
|
||||
@@ -32,7 +32,7 @@ JSON class into byte-sized characters during deserialization.
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `StringType` (`std::string`), the default value for `string_t` is `#!cpp std::string`.
|
||||
With the default values for `StringType` (`std::string`), the default type for `string_t` is `#!cpp std::string`.
|
||||
|
||||
### Encoding
|
||||
|
||||
|
||||
@@ -1,5 +1,5 @@
|
||||
<!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/string_t/" rel="canonical"><link href=../start_pos/ rel=prev><link href=../swap/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>string_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> strings.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> strings as follows:</p> <blockquote> <p>A string is a sequence of zero or more Unicode characters.</p> </blockquote> <p>To store strings in C++, a type is defined by the template parameter described below. Unicode values are split by the <abbr title="JavaScript Object Notation">JSON</abbr> class into byte-sized characters during deserialization.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>StringType</code></dt> <dd> <p>the container to store strings (e.g., <code>std::string</code>). Note this container is used for keys/names in objects, see <a href=../object_t/ >object_t</a>.</p> <p><code>StringType</code> must have a <code>char</code>-compatible <code>value_type</code>: the library relies on <abbr title="Unicode Transformation Format">UTF</abbr>-8/<code>char</code>-based storage and processing internally, so <code>std::wstring</code>, <code>std::u16string</code>, and <code>std::u32string</code> are <strong>not</strong> valid choices for <code>StringType</code>. To work with wide-character data, convert it to/from <abbr title="Unicode Transformation Format">UTF</abbr>-8 at the boundary instead -- see the <abbr title="Frequently Asked Questions">FAQ</abbr>'s <a href=../../../home/faq/#wide-string-handling>wide string handling</a> section for a conversion recipe.</p> <p>Beyond the character type, the library expects a substantial part of the <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> interface (contiguous null-terminated <code>data()</code>, <code>substr()</code>, <code>find()</code>, <code>append()</code>, ...). See <a href=../../../features/types/template_parameters/#stringtype>Template Parameter Requirements</a> for the full list and for the string types that are known to work.</p> </dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>StringType</code> (<code>std::string</code>), the default value for <code>string_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>.</p> <h3 id=encoding>Encoding<a class=headerlink href=#encoding title="Permanent link">¶</a></h3> <p>Strings are stored in <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoding. Therefore, functions like <code>std::string::size()</code> or <code>std::string::length()</code> return the number of bytes in the string rather than the number of characters or glyphs.</p> <h3 id=string-comparison>String comparison<a class=headerlink href=#string-comparison title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> states:</p> <blockquote> <p>Software implementations are typically required to test names of object members for equality. Implementations that transform the textual representation into sequences of Unicode code units and then perform the comparison numerically, code unit by code unit, are interoperable in the sense that implementations will agree in all cases on equality or inequality of two strings. For example, implementations that compare strings with escaped characters unconverted may incorrectly find that <code>"a\\b"</code> and <code>"a\u005Cb"</code> are not equal.</p> </blockquote> <p>This implementation is interoperable as it does compare strings code unit by code unit.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>String values are stored as pointers in a <code>basic_json</code> type. That is, for any access to string values, a pointer of type <code>string_t*</code> must be dereferenced.</p> <h3 id=cross-basic_json-conversion-requirements>Cross-<code>basic_json</code> conversion requirements<a class=headerlink href=#cross-basic_json-conversion-requirements title="Permanent link">¶</a></h3> <p>When converting a string value from one <code>basic_json</code> specialization to another via the <a href=../basic_json/ >converting constructor</a> (overload 4), the target <code>string_t</code> must be directly constructible from the source <code>basic_json</code>'s <code>string_t</code> type. If this requirement is not met, the conversion does not fail; instead, the string is silently converted as an array of character codes, which is incorrect. See <a href="https://github.com/nlohmann/json/issues/3425">issue #3425</a> for details and an example.</p> <h2 id=examples>Examples<a class=headerliLine truncated
|
||||
</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> strings.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> strings as follows:</p> <blockquote> <p>A string is a sequence of zero or more Unicode characters.</p> </blockquote> <p>To store strings in C++, a type is defined by the template parameter described below. Unicode values are split by the <abbr title="JavaScript Object Notation">JSON</abbr> class into byte-sized characters during deserialization.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">¶</a></h2> <dl> <dt><code>StringType</code></dt> <dd> <p>the container to store strings (e.g., <code>std::string</code>). Note this container is used for keys/names in objects, see <a href=../object_t/ >object_t</a>.</p> <p><code>StringType</code> must have a <code>char</code>-compatible <code>value_type</code>: the library relies on <abbr title="Unicode Transformation Format">UTF</abbr>-8/<code>char</code>-based storage and processing internally, so <code>std::wstring</code>, <code>std::u16string</code>, and <code>std::u32string</code> are <strong>not</strong> valid choices for <code>StringType</code>. To work with wide-character data, convert it to/from <abbr title="Unicode Transformation Format">UTF</abbr>-8 at the boundary instead -- see the <abbr title="Frequently Asked Questions">FAQ</abbr>'s <a href=../../../home/faq/#wide-string-handling>wide string handling</a> section for a conversion recipe.</p> <p>Beyond the character type, the library expects a substantial part of the <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> interface (contiguous null-terminated <code>data()</code>, <code>substr()</code>, <code>find()</code>, <code>append()</code>, ...). See <a href=../../../features/types/template_parameters/#stringtype>Template Parameter Requirements</a> for the full list and for the string types that are known to work.</p> </dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">¶</a></h3> <p>With the default values for <code>StringType</code> (<code>std::string</code>), the default type for <code>string_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>.</p> <h3 id=encoding>Encoding<a class=headerlink href=#encoding title="Permanent link">¶</a></h3> <p>Strings are stored in <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoding. Therefore, functions like <code>std::string::size()</code> or <code>std::string::length()</code> return the number of bytes in the string rather than the number of characters or glyphs.</p> <h3 id=string-comparison>String comparison<a class=headerlink href=#string-comparison title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> states:</p> <blockquote> <p>Software implementations are typically required to test names of object members for equality. Implementations that transform the textual representation into sequences of Unicode code units and then perform the comparison numerically, code unit by code unit, are interoperable in the sense that implementations will agree in all cases on equality or inequality of two strings. For example, implementations that compare strings with escaped characters unconverted may incorrectly find that <code>"a\\b"</code> and <code>"a\u005Cb"</code> are not equal.</p> </blockquote> <p>This implementation is interoperable as it does compare strings code unit by code unit.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">¶</a></h3> <p>String values are stored as pointers in a <code>basic_json</code> type. That is, for any access to string values, a pointer of type <code>string_t*</code> must be dereferenced.</p> <h3 id=cross-basic_json-conversion-requirements>Cross-<code>basic_json</code> conversion requirements<a class=headerlink href=#cross-basic_json-conversion-requirements title="Permanent link">¶</a></h3> <p>When converting a string value from one <code>basic_json</code> specialization to another via the <a href=../basic_json/ >converting constructor</a> (overload 4), the target <code>string_t</code> must be directly constructible from the source <code>basic_json</code>'s <code>string_t</code> type. If this requirement is not met, the conversion does not fail; instead, the string is silently converted as an array of character codes, which is incorrect. See <a href="https://github.com/nlohmann/json/issues/3425">issue #3425</a> for details and an example.</p> <h2 id=examples>Examples<a class=headerlinLine truncated
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><iomanip></span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
@@ -10,4 +10,4 @@
|
||||
<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><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o><</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>json</span><span class=o>::</span><span class=n>string_t</span><span class=o>>::</span><span class=n>value</span><span class=w> </span><span class=o><<</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../object_t/ >object_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects (and their keys, which are also <code>string_t</code>)</li> <li><a href=../binary_t/ >binary_t</a> the type used to store binary values</li> <li><a href=../get_ptr/ >get_ptr</a> returns a pointer to the stored string value</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Removed the requirement that <code>string_t</code> be implicitly convertible from <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>, which the <abbr title="Binary JSON">BSON</abbr> writer and the <abbr title="Universal Binary JSON">UBJSON</abbr> reader relied on, in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- 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 - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="Line truncated
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||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../object_t/ >object_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects (and their keys, which are also <code>string_t</code>)</li> <li><a href=../binary_t/ >binary_t</a> the type used to store binary values</li> <li><a href=../get_ptr/ >get_ptr</a> returns a pointer to the stored string value</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Removed the requirement that <code>string_t</code> be implicitly convertible from <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>, which the <abbr title="Binary JSON">BSON</abbr> writer and the <abbr title="Universal Binary JSON">UBJSON</abbr> reader relied on, in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- 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 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path dLine truncated
|
||||
@@ -32,7 +32,7 @@ for the string types that are known to work.
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `StringType` (`std::string`), the default value for `string_t` is `std::string`.
|
||||
With the default values for `StringType` (`std::string`), the default type for `string_t` is `std::string`.
|
||||
|
||||
### Encoding
|
||||
|
||||
|
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@@ -18,7 +18,8 @@ When enabled, comparisons involving at least one discarded JSON value yield resu
|
||||
| `>=` | `#!cpp true` |
|
||||
| `>` | `#!cpp false` |
|
||||
|
||||
Otherwise, comparisons involving at least one discarded JSON value always yield `#!cpp false`.
|
||||
Otherwise, comparisons involving at least one discarded JSON value yield `#!cpp false`, except for `!=`, which is the
|
||||
negation of `==` and yields `#!cpp true`.
|
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|
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## Default definition
|
||||
|
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|
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@@ -1,7 +1,7 @@
|
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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/macros/json_use_legacy_discarded_value_comparison/" rel="canonical"><link href=../json_use_implicit_conversions/ rel=prev><link href=../json_use_objects_for_enum_keyed_maps/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON - 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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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> JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON </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 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1.61-.59 3.09-1.56 4.23l.2Line truncated
|
||||
</code></pre></div> <p>This macro enables the (incorrect) legacy comparison behavior of discarded <abbr title="JavaScript Object Notation">JSON</abbr> values. Possible values are <code>1</code> to enable or <code>0</code> to disable (default).</p> <p>When enabled, comparisons involving at least one discarded <abbr title="JavaScript Object Notation">JSON</abbr> value yield results as follows:</p> <table> <thead> <tr> <th><strong>Operator</strong></th> <th><strong>Result</strong></th> </tr> </thead> <tbody> <tr> <td><code>==</code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><code>!=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code><</code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><code><=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code>>=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code>></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> </tbody> </table> <p>Otherwise, comparisons involving at least one discarded <abbr title="JavaScript Object Notation">JSON</abbr> value always yield <code class=highlight><span class=nb>false</span></code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">¶</a></h2> <p>The default value is <code>0</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 0</span>
|
||||
</code></pre></div> <p>This macro enables the (incorrect) legacy comparison behavior of discarded <abbr title="JavaScript Object Notation">JSON</abbr> values. Possible values are <code>1</code> to enable or <code>0</code> to disable (default).</p> <p>When enabled, comparisons involving at least one discarded <abbr title="JavaScript Object Notation">JSON</abbr> value yield results as follows:</p> <table> <thead> <tr> <th><strong>Operator</strong></th> <th><strong>Result</strong></th> </tr> </thead> <tbody> <tr> <td><code>==</code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><code>!=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code><</code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><code><=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code>>=</code></td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td><code>></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> </tbody> </table> <p>Otherwise, comparisons involving at least one discarded <abbr title="JavaScript Object Notation">JSON</abbr> value yield <code class=highlight><span class=nb>false</span></code>, except for <code>!=</code>, which is the negation of <code>==</code> and yields <code class=highlight><span class=nb>true</span></code>.</p> <h2 id=default-definition>Default definition<a class=headerlink href=#default-definition title="Permanent link">¶</a></h2> <p>The default value is <code>0</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 0</span>
|
||||
</code></pre></div> <p>When the macro is not defined, the library will define it to its default value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <div class="admonition warning"> <p class=admonition-title>Inconsistent behavior in C++20 and beyond</p> <p>When targeting C++20 or above, enabling the legacy comparison behavior is <em>strongly</em> discouraged.</p> <ul> <li>The 3-way comparison operator (<code><=></code>) will always give the correct result (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>partial_ordering</span><span class=o>::</span><span class=n>unordered</span></code>) regardless of the value of <code>JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON</code>.</li> <li>Overloads for the equality and relational operators emulate the legacy behavior.</li> </ul> <p>Code outside your control may use either 3-way comparison or the equality and relational operators, resulting in inconsistent and unpredictable behavior.</p> <p>See <a href=../../basic_json/operator_spaceship/ ><code>operator<=></code></a> for more information on 3-way comparison.</p> </div> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <p>The legacy comparison behavior is deprecated and may be removed in a future major version release.</p> <p>New code should not depend on it and existing code should try to remove or rewrite expressions relying on it.</p> <p>See the <a href=../../../integration/migration_guide/#miscellaneous-functions>migration guide</a> for how to update existing code.</p> </div> <div class="admonition hint"> <p class=admonition-title>CMake option</p> <p>Legacy comparison can also be controlled with the CMake option <a href=../../../integration/cmake/#json_legacydiscardedvaluecomparison><code>JSON_LegacyDiscardedValueComparison</code></a> (<code>OFF</code> by default) which defines <code>JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON</code> accordingly.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <details class=example> <summary>Example</summary> <p>The code below switches on the legacy discarded value comparison behavior in the library.</p> <div class=highlight><pre><span></span><code><span class=cp>#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 1</span>
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json.hpp></span>
|
||||
|
||||
<span class=p>...</span>
|
||||
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../../../integration/cmake/#json_legacydiscardedvaluecomparison><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_LegacyDiscardedValueComparison</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.11.0.</li> <li>Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> so <code><=</code> and <code>>=</code> also emulate the legacy behavior in C++20 when the <abbr title="JavaScript Object Notation">JSON</abbr> value is the right-hand operand of a scalar comparison; before, only the 3-way-comparison-rewritten candidate was found, which yielded <code class=highlight><span class=nb>false</span></code> instead of <code class=highlight><span class=nb>true</span></code>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 4, 2026 09:46:21 UTC">October 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesomLine truncated
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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li><a href=../../../integration/cmake/#json_legacydiscardedvaluecomparison><span class=twemoji><svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M11.769.066.067 23.206l12.76-10.843zm11.438 23.868L7.471 17.587 0 23.934zm.793-.198L12.298.463l1.719 19.24zM12.893 12.959l-5.025 4.298 5.62 2.248z"/></svg></span> JSON_LegacyDiscardedValueComparison</a> - CMake option to control the macro</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">¶</a></h2> <ul> <li>Added in version 3.11.0.</li> <li>Fixed in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> so <code><=</code> and <code>>=</code> also emulate the legacy behavior in C++20 when the <abbr title="JavaScript Object Notation">JSON</abbr> value is the right-hand operand of a scalar comparison; before, only the 3-way-comparison-rewritten candidate was found, which yielded <code class=highlight><span class=nb>false</span></code> instead of <code class=highlight><span class=nb>true</span></code>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 15:40:55 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesLine truncated
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||||
@@ -17,7 +17,7 @@ When enabled, comparisons involving at least one discarded JSON value yield resu
|
||||
| `>=` | `true` |
|
||||
| `>` | `false` |
|
||||
|
||||
Otherwise, comparisons involving at least one discarded JSON value always yield `false`.
|
||||
Otherwise, comparisons involving at least one discarded JSON value yield `false`, except for `!=`, which is the negation of `==` and yields `true`.
|
||||
|
||||
## Default definition
|
||||
|
||||
|
||||
Reference in new issue
Block a user