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2026年01月20日 03時05分18秒
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<div class="identifier-type">function</div><div class="header"><format></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">vformat</span><span class="cpp cpp20" title="C++20で追加">(C++20)</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="n"><a href="../string/basic_string.html">string</a></span>
<span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="n"><a href="../string_view/basic_string_view.html">string_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="basic_format_args.html">format_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++20</span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n"><a href="../string/basic_string.html">string</a></span>
<span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="n"><a href="../string_view/basic_string_view.html">string_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="basic_format_args.html">format_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++26</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">wstring</a></span>
<span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="n"><a href="../string_view/basic_string_view.html">wstring_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="basic_format_args.html">wformat_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++20</span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n"><a href="../string/basic_string.html">wstring</a></span>
<span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="n"><a href="../string_view/basic_string_view.html">wstring_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="basic_format_args.html">wformat_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++26</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">string</a></span>
<span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../locale/locale.html">locale</a></span><span class="o">&</span><span class="w"> </span><span class="n">loc</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="../string_view/basic_string_view.html">string_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="basic_format_args.html">format_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">);</span><span class="w"> </span><span class="c1">// (3) C++20</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">wstring</a></span>
<span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../locale/locale.html">locale</a></span><span class="o">&</span><span class="w"> </span><span class="n">loc</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="../string_view/basic_string_view.html">wstring_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="basic_format_args.html">wformat_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">);</span><span class="w"> </span><span class="c1">// (4) C++20</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>書式文字列<code>fmt</code>に従ったフォーマットで<code>args</code>の文字列表現を文字列オブジェクトで返す。</p>
<ul>
<li>(1): マルチバイト文字列版</li>
<li>(2): ワイド文字列版</li>
<li>(3): マルチバイト文字列版 (ロケール指定あり)</li>
<li>(4): ワイド文字列版 (ロケール指定あり)</li>
</ul>
<p><code><a href="format.html">std::format()</a></code>関数のフォーマット引数を実行時文字列にしたバージョンであり、<code><a href="format.html">std::format()</a></code>関数の内部で使用される。</p>
<p><code><a href="format.html">std::format()</a></code>のような関数を自作する場合にこの関数を使って実装すると便利であるほか、実行時文字列でフォーマット引数を構築したい場合にも利用できる。</p>
<p>C++26以降は、実行時文字列のフォーマット引数を使用したい場合は、<code><a href="runtime_format.html">std::runtime_format()</a></code>関数を使用できる。</p>
<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><code>args</code>の文字列表現を保持する文字列</p>
<h2><a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a></h2>
<p>フォーマット実行時に失敗した場合、<code><a href="format_error.html">format_error</a></code>を投げる。</p>
<h2>例</h2>
<p><div class="yata" id="aecb4732974ae99fde75697f07409283d005c8a2"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../format.html"><format></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="../string/basic_string.html">std::string</a></span><span class="w"> </span><span class="n">fmt</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"0x{:x} 0b{:04b}"</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">std::string</a></span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::vformat</span></span><span class="p">(</span><span class="n">fmt</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="make_format_args.html">std::make_format_args</a></span><span class="p">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><pre><code>0xa 0b0110
</code></pre></p>
<h2>実装例</h2>
<p><div class="codehilite"><pre><span></span><code><span class="n"><a href="../string/basic_string.html">string</a></span><span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="n"><a href="../string_view/basic_string_view.html">string_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="basic_format_args.html">format_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">string</a></span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="vformat_to.html">vformat_to</a></span><span class="p">(</span><span class="n"><a href="../iterator/back_inserter.html">back_inserter</a></span><span class="p">(</span><span class="n">str</span><span class="p">),</span><span class="w"> </span><span class="n">fmt</span><span class="p">.</span><span class="n">str</span><span class="p">,</span><span class="w"> </span><span class="n">args</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="p">}</span>
<span class="n"><a href="../string/basic_string.html">string</a></span><span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="n"><a href="../string_view/basic_string_view.html">wstring_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="basic_format_args.html">wformat_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">wstring</a></span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="vformat_to.html">vformat_to</a></span><span class="p">(</span><span class="n"><a href="../iterator/back_inserter.html">back_inserter</a></span><span class="p">(</span><span class="n">str</span><span class="p">),</span><span class="w"> </span><span class="n">fmt</span><span class="p">.</span><span class="n">str</span><span class="p">,</span><span class="w"> </span><span class="n">args</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="p">}</span>
<span class="n"><a href="../string/basic_string.html">string</a></span><span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../locale/locale.html">locale</a></span><span class="o">&</span><span class="w"> </span><span class="n">loc</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../string_view/basic_string_view.html">string_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="basic_format_args.html">format_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">string</a></span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="vformat_to.html">vformat_to</a></span><span class="p">(</span><span class="n">loc</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../iterator/back_inserter.html">back_inserter</a></span><span class="p">(</span><span class="n">str</span><span class="p">),</span><span class="w"> </span><span class="n">fmt</span><span class="p">.</span><span class="n">str</span><span class="p">,</span><span class="w"> </span><span class="n">args</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="p">}</span>
<span class="n"><a href="../string/basic_string.html">string</a></span><span class="w"> </span><span class="nf">vformat</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../locale/locale.html">locale</a></span><span class="o">&</span><span class="w"> </span><span class="n">loc</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../string_view/basic_string_view.html">wstring_view</a></span><span class="w"> </span><span class="n">fmt</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="basic_format_args.html">wformat_args</a></span><span class="w"> </span><span class="n">args</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">wstring</a></span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="vformat_to.html">vformat_to</a></span><span class="p">(</span><span class="n">loc</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../iterator/back_inserter.html">back_inserter</a></span><span class="p">(</span><span class="n">str</span><span class="p">),</span><span class="w"> </span><span class="n">fmt</span><span class="p">.</span><span class="n">str</span><span class="p">,</span><span class="w"> </span><span class="n">args</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++20</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: 17</li>
<li><a href="../../implementation.html#gcc">GCC</a>: 13</li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: ??</li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://timsong-cpp.github.io/cppwp/format" target="_blank">Working Draft, Standard for Programming Language C++ [format]</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html" target="_blank">P0645R10 Text Formatting</a></li>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html" target="_blank">P3391R2 <code>constexpr std::format</code></a><ul>
<li>C++26から非ロケール版が<code>constexpr</code>に対応した</li>
</ul>
</li>
</ul></div>
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