mirror of
https://github.com/nlohmann/json.git
synced 2026-10-16 03:07:12 +00:00
deploy: 4e294f4b18
This commit is contained in:
1 parent
dcc7a74a18
commit
98c9bea1d1
105 files changed
+537
-508
No files matched your search
@@ -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/number_float_t/" rel="canonical"><link href=../merge_patch/ rel=prev><link href=../number_integer_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>number_float_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonnumber_float_t class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> number_float_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5Line truncated
|
||||
</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
|
||||
</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
|
||||
<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>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
|
||||
</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
|
||||
@@ -16,13 +16,13 @@ To store floating-point numbers in C++, a type is defined by the template parame
|
||||
|
||||
## Template parameters
|
||||
|
||||
`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).
|
||||
`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).
|
||||
|
||||
## Notes
|
||||
|
||||
### Default type
|
||||
|
||||
With the default values for `NumberFloatType` (`double`), the default value for `number_float_t` is `double`.
|
||||
With the default values for `NumberFloatType` (`double`), the default type for `number_float_t` is `double`.
|
||||
|
||||
### Default behavior
|
||||
|
||||
@@ -35,7 +35,7 @@ With the default values for `NumberFloatType` (`double`), the default value for
|
||||
|
||||
> 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.
|
||||
|
||||
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`](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`.
|
||||
|
||||
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`.
|
||||
|
||||
|
||||
Reference in new issue
Block a user