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<div class="identifier-type">function</div><div class="header"><cmath></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">fmaximum_num</span><span class="cpp cpp26" title="C++26で追加">(C++26)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n"><i>floating-point-type</i></span>
<span class="w"> </span><span class="nf">fmaximum_num</span><span class="p">(</span><span class="n"><i>floating-point-type</i></span><span class="w"> </span><span class="n">x</span><span class="p">,</span>
<span class="w"> </span><span class="n"><i>floating-point-type</i></span><span class="w"> </span><span class="n">y</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++26</span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n"><i>Promoted</i></span>
<span class="w"> </span><span class="nf">fmaximum_num</span><span class="p">(</span><span class="n"><i>Arithmetic1</i></span><span class="w"> </span><span class="n">x</span><span class="p">,</span>
<span class="w"> </span><span class="n"><i>Arithmetic2</i></span><span class="w"> </span><span class="n">y</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++26</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>浮動小数点数型の最大値を求める。</p>
<ul>
<li>(1) : 浮動小数点数型に対する<a class="cpprefjp-defined-word" data-desc="同名の関数を異なる引数・テンプレート・制約などで複数定義すること。または同名の関数の集合">オーバーロード</a></li>
<li>(2) : 算術型に対する<a class="cpprefjp-defined-word" data-desc="同名の関数を異なる引数・テンプレート・制約などで複数定義すること。または同名の関数の集合">オーバーロード</a> (大きい精度にキャストして計算される。整数は<code>double</code>で計算される)</li>
</ul>
<p>同じ目的のほかの関数との比較は以下。</p>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>関数名</th>
<th>-0.0 と +0.0 の比較</th>
<th>NaN を含む場合の挙動</th>
<th>備考</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="fmax.html">fmax</a></code></td>
<td><a class="cpprefjp-defined-word" data-desc="未規定の動作。事前の断りなく処理系によって異なる動作をする" href="../../implementation-compliance.html#dfn-unspecified-behavior">未規定</a></td>
<td>NaN でない方を返す</td>
<td></td>
</tr>
<tr>
<td><code><a href="fmaximum.html">fmaximum</a></code></td>
<td>+0.0 を返す</td>
<td>NaN を返す</td>
<td>エラー伝播を優先</td>
</tr>
<tr>
<td><code><a href="">fmaximum_num</a></code></td>
<td>+0.0 を返す</td>
<td>NaN でない方を返す</td>
<td>数値を優先</td>
</tr>
</tbody>
</table>
<h2><a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a></h2>
<p>引数の最大値を返す。</p>
<h2>備考</h2>
<ul>
<li><a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a>は正確で、現在の丸めモードに依存しない。</li>
<li>処理系が IEC 60559 に準拠している場合（<code><a href="../limits/numeric_limits.html">std::numeric_limits</a><T>::<a href="../limits/numeric_limits/is_iec559.html">is_iec559</a>() != false</code>）、以下の規定が追加される。<ul>
<li>引数の1つが NaN の場合 NaN でない方を返す。</li>
<li>引数が2つとも NaN の場合 NaN を返す。</li>
</ul>
</li>
<li><code>-0.0</code>と<code>+0.0</code>の比較では、<code>+0.0</code>を返す。</li>
<li>IEEE 754 の <code>maximumNum</code> に対応する。</li>
</ul>
<h2>例</h2>
<p><div class="yata" id="a99af6f4be4c69888e51dfb6951a1ade0ffd2939"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../print.html"><print></a></span>
<span class="cp">#include <a href="../cmath.html"><cmath></a></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"fmaximum_num( 0.0, -1.0) = {:+}"</span><span class="p">,</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::fmaximum_num</span></span><span class="p">(</span><span class="mf">0.0</span><span class="p">,</span><span class="w"> </span><span class="mf">-1.0</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"fmaximum_num(-0.0, +0.0) = {:+}"</span><span class="p">,</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::fmaximum_num</span></span><span class="p">(</span><span class="mf">-0.0</span><span class="p">,</span><span class="w"> </span><span class="o">+</span><span class="mf">0.0</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"fmaximum_num( 0.0, +1.0) = {:+}"</span><span class="p">,</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::fmaximum_num</span></span><span class="p">(</span><span class="mf">0.0</span><span class="p">,</span><span class="w"> </span><span class="o">+</span><span class="mf">1.0</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"fmaximum_num( 0.0, nan) = {:+}"</span><span class="p">,</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::fmaximum_num</span></span><span class="p">(</span><span class="mf">0.0</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="nanf.html">std::nan</a></span><span class="p">(</span><span class="s">""</span><span class="p">)));</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"fmaximum_num( nan, nan) = {:+}"</span><span class="p">,</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::fmaximum_num</span></span><span class="p">(</span><span class="n"><a href="nanf.html">std::nan</a></span><span class="p">(</span><span class="s">""</span><span class="p">),</span><span class="w"> </span><span class="n"><a href="nanf.html">std::nan</a></span><span class="p">(</span><span class="s">""</span><span class="p">)));</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力例</h3>
<p><pre><code>fmaximum_num( 0.0, -1.0) = +0
fmaximum_num(-0.0, +0.0) = +0
fmaximum_num( 0.0, +1.0) = +1
fmaximum_num( 0.0, nan) = +0
fmaximum_num( nan, nan) = +nan
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++26</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: 21.0 <span aria-label="未実装" role="img" title="未実装">❌</span></li>
<li><a href="../../implementation.html#gcc">GCC</a>: 15 <span aria-label="未実装" role="img" title="未実装">❌</span></li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: 2022 Update 14 <span aria-label="未実装" role="img" title="未実装">❌</span></li>
</ul>
<h2>関連項目</h2>
<ul>
<li><code><a href="fmax.html">fmax</a></code></li>
<li><code><a href="fmaximum.html">fmaximum</a></code></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3008r6.html" target="_blank">P3008R6 Atomic floating-point min/max</a></li>
</ul></div>
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