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<header data-kunai-mdinfo="{"meta": {"header": ["format"], "id-type": ["class template"], "namespace": ["std"], "cpp": ["cpp20"]}, "sources": [{"id": "f0f1f0a4ab5ebbae12a3bb9c2578b97179eb8305", "source": "#include <iostream>\n#include <format>\n\nenum color { red, green, blue };\n\nconst char* color_names[] = { \"red\", \"green\", \"blue\" };\n\ntemplate<>\nstruct std::formatter<color> : std::formatter<const char*> {\n auto format(color c, std::format_context& ctx) const {\n return std::formatter<const char*>::format(color_names[c], ctx);\n }\n};\n\nint main()\n{\n std::cout << std::format(\"{}\", red) << std::endl;\n}\n"}, {"id": "795293b1e8ac834d0cb3e053df1bcc3f84ab3a64", "source": "#include <iostream>\n#include <format>\n\nenum color { red, green, blue };\n\nconst char* color_names[] = { \"red\", \"green\", \"blue\" };\nconst char* jp_color_names[] = { \"\u8d64\", \"\u7dd1\", \"\u9752\" };\n\ntemplate<>\nstruct std::formatter<color> {\n bool is_jp = false;\n\n // \u30b3\u30f3\u30d1\u30a4\u30eb\u6642\u306e\u66f8\u5f0f\u6587\u5b57\u5217\u306e\u89e3\u6790\u304c\u3042\u308b\u305f\u3081\u3001\n // constexpr\u306b\u3059\u308b\u5fc5\u8981\u304c\u3042\u308b\u3002\n // \u3053\u306e\u95a2\u6570\u306b\u6e21\u3055\u308c\u308b\u30d1\u30e9\u30e1\u30fc\u30bf\u306f\u3001{:%j}\u306e%\u4ee5\u964d\u3002\n // \u89e3\u6790\u304c\u304a\u308f\u3063\u305f\u5834\u6240\u3092\u6307\u3059\u30a4\u30c6\u30ec\u30fc\u30bf\u3092\u8fd4\u3059\u3002\n constexpr auto parse(std::format_parse_context& ctx) {\n auto it = ctx.begin();\n if (*it == '%') {\n ++it;\n if (*it == 'j') {\n is_jp = true;\n }\n else if (*it == 'e') {\n is_jp = false;\n }\n ++it;\n }\n return it;\n }\n\n // format()\u95a2\u6570\u306f\u66f8\u5f0f\u306e\u60c5\u5831\u3092\u3082\u305f\u306a\u3044\u3002\n // parse()\u95a2\u6570\u3067\u89e3\u6790\u3057\u305f\u66f8\u5f0f\u3092\u30e1\u30f3\u30d0\u5909\u6570\u3067\u4fdd\u6301\u3057\u3066\u304a\u3044\u3066\u3001\n // \u305d\u308c\u3092\u3082\u3068\u306b\u66f8\u5f0f\u5316\u3059\u308b\n auto format(color c, std::format_context& ctx) const {\n return std::format_to(ctx.out(), \"{}\",\n is_jp ? jp_color_names[c] : color_names[c]\n );\n }\n};\n\nint main()\n{\n std::cout << std::format(\"{:%j} {:%e}\", red, blue) << std::endl;\n}\n"}, {"id": "d25188a377882c9f6e282ac92bd1f5a4bd0c3fe9", "source": "#include <iostream>\n#include <format>\n\nstruct Point {\n float x, y;\n};\n\ntemplate<>\nstruct std::formatter<Point> : std::formatter<std::string> {\n auto format(Point p, std::format_context& ctx) const {\n return std::formatter<std::string>::format(\n std::format(\"[{}, {}]\", p.x, p.y),\n ctx);\n }\n};\n\nint main()\n{\n std::cout << std::format(\"{}\", Point{1.2f, 3.4f}) << std::endl;\n}\n"}], "page_id": ["reference", "format", "formatter"]}">
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最終更新日時(UTC):
<span itemprop="datePublished" content="2024-09-17T22:26:07">
2024年09月17日 22時26分07秒
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<span itemprop="author" itemscope itemtype="http://schema.org/Person">
<span itemprop="name">Akira Takahashi</span>
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が更新
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<div class="identifier-type">class template</div><div class="header"><format></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">formatter</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="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">charT</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kt">char</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">formatter</span><span class="p">;</span><span class="w"> </span><span class="c1">// (1) C++20</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="n"><a href="../ranges/input_range.html">ranges::input_range</a></span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">charT</span><span class="o">></span>
<span class="w"> </span><span class="k">requires</span><span class="w"> </span><span class="p">(</span><span class="n"><a href="format_kind.html">format_kind</a></span><span class="o"><</span><span class="n">R</span><span class="o">></span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n"><a href="range_format.html">range_format</a></span><span class="o">::</span><span class="n">disabled</span><span class="p">)</span><span class="w"> </span><span class="o">&&</span>
<span class="w"> </span><span class="n"><a href="formattable.html">formattable</a></span><span class="o"><</span><span class="n"><a href="../ranges/range_reference_t.html">ranges::range_reference_t</a></span><span class="o"><</span><span class="n">R</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="n">charT</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">formatter</span><span class="o"><</span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">charT</span><span class="o">></span>
<span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n"><a href="range-default-formatter.html">range-default-formatter</a></span><span class="o"><</span><span class="n"><a href="format_kind.html">format_kind</a></span><span class="o"><</span><span class="n">R</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">charT</span><span class="o">></span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="p">};</span><span class="w"> </span><span class="c1">// (2) C++23</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">charT</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="formattable.html">formattable</a></span><span class="o"><</span><span class="n">charT</span><span class="o">></span><span class="p">...</span><span class="w"> </span><span class="n">Ts</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">formatter</span><span class="o"><</span><span class="n"><a href="../utility/pair.html">pair</a></span><span class="o">-</span><span class="k">or</span><span class="o">-</span><span class="n"><a href="../tuple/tuple.html">tuple</a></span><span class="o"><</span><span class="n">Ts</span><span class="p">...</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="n">charT</span><span class="o">></span><span class="p">;</span><span class="w"> </span><span class="c1">// (3) C++23</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">charT</span><span class="p">,</span>
<span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="formattable.html">formattable</a></span><span class="o"><</span><span class="n">charT</span><span class="o">></span><span class="w"> </span><span class="n">Container</span><span class="p">,</span>
<span class="w"> </span><span class="k">class</span><span class="p">...</span><span class="w"> </span><span class="n">U</span><span class="o">></span>
<span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">formatter</span><span class="o"><</span><span class="n">adaptor</span><span class="o">-</span><span class="n">type</span><span class="o"><</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Container</span><span class="p">,</span><span class="w"> </span><span class="n">U</span><span class="p">...</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="n">charT</span><span class="o">></span><span class="p">;</span><span class="w"> </span><span class="c1">// (4) C++23</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>フォーマット引数の個々の型に対応する書式文字列の解析と値のフォーマットを担うクラス。</p>
<ul>
<li>(1) : デフォルトのフォーマット</li>
<li>(2) : Range用のフォーマット。実装は<code><a href="range-default-formatter.html">range-default-formatter</a></code>クラスが行う</li>
<li>(3) : <code><a href="../utility/pair.html">std::pair</a></code>と<code><a href="../tuple/tuple.html">std::tuple</a></code>に対する特殊化</li>
<li>(4) : <a class="cpprefjp-defined-word" data-desc="コンテナをラップしたクラス。一部のコンテナインタフェースをもたない場合がある">コンテナアダプタ</a>である<code><a href="../queue/queue.html">std::queue</a></code>、<code><a href="../queue/priority_queue.html">std::priority_queue</a></code>、<code><a href="../stack/stack.html">std::stack</a></code>に対する特殊化</li>
</ul>
<p>(1)は、<code>charT</code>を<code>char</code>または<code>wchar_t</code>とすると、標準で以下の特殊化が利用できる。</p>
<ul>
<li><code>template<> struct formatter<charT, charT></code></li>
<li><code>template<> struct formatter<char, wchar_t></code></li>
<li><code>template<> struct formatter<charT*, charT></code></li>
<li><code>template<> struct formatter<const charT*, charT></code></li>
<li><code>template<size_t N> struct formatter<const charT[N], charT></code></li>
<li><code>template<class traits, class Allocator> struct formatter<<a href="../string/basic_string.html">basic_string</a><charT, traits, Allocator>, charT></code></li>
<li><code>template<class traits> struct formatter<<a href="../string_view/basic_string_view.html">basic_string_view</a><charT, traits>, charT></code></li>
<li>第1テンプレート引数が<code>nullptr_t</code>, <code>void*</code>, <code>const void*</code>, <code>bool</code>, すべての<a class="cpprefjp-defined-word" data-desc="型をconstおよび・もしくはvolatileで修飾すること">CV修飾</a>されない標準の整数型, 拡張整数型, 浮動小数点数型であり、第2テンプレート引数が<code>charT</code>であるもの。</li>
</ul>
<p>さらに、ユーザーが<code>formatter</code>を特殊化した場合、それも有効である。</p>
<p>標準でも<a class="cpprefjp-defined-word" data-desc="プログラム定義。ユーザー（プログラマ）によって定義されること（標準ライブラリで定義されるものを除く）">ユーザー定義</a>でも特殊化されない場合、その型に対する<code>formatter</code>は無効であり、そのような型はフォーマット関数の引数にできない。</p>
<p>ワイド文字列とマルチバイト文字列を相互に変換するような特殊化は意図的に用意されていないが、ユーザーが用意することは禁止していない。</p>
<h2>ユーザーの型で<code>formatter</code>を特殊化する場合の要件</h2>
<p><code>formatter</code>の有効な特殊化はFormatter要件を満たす必要がある。</p>
<p>型<code>F</code>がFormatter要件を満たすとは、次のことをいう。</p>
<ul>
<li><code>F</code>は<code>Cpp17DefaultConstructible</code>、<code>Cpp17CopyConstructible</code>、<code>Cpp17CopyAssignable</code>、<code>Cpp17Destructible</code>であること</li>
</ul>
<p>さらに、以下の条件を満たすこと</p>
<ol>
<li>式 <code>f.parse(pc)</code> が有効であり、<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>の型が<code>PC::iterator</code>である</li>
<li><a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[pc.begin(), pc.end())</code>を解析して<code>format_error</code>を投げるか、解析が終わった位置を指すイテレータを返す</li>
</ul>
</li>
<li>式 <code>cf.format(t, fc)</code> が有効であり、<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>の型が<code>FC::iterator</code>である</li>
<li>フォーマット結果を<code>fc.out()</code>へ出力し、出力後のイテレータを返す</li>
<li>出力は<code>t</code>、<code>fc.locale()</code>、最後に呼び出された<code>f.parse(pc)</code>の<a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[pc.begin(), pc.end())</code>以外に依存しない</li>
</ul>
</li>
<li>式 <code>cf.format(u, fc)</code> が有効であり、<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>が<code>FC::iterator</code>である</li>
<li>フォーマット結果を<code>fc.out()</code>へ出力し、出力後のイテレータを返す</li>
<li>出力は<code>u</code>、<code>fc.locale()</code>、最後に呼び出された<code>f.parse(pc)</code>の<a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[pc.begin(), pc.end())</code>以外に依存しない</li>
<li><code>u</code>を変更しない</li>
</ul>
</li>
</ol>
<p>条件内の各要素を、以下のように定義する。</p>
<ul>
<li>文字の型を<code>charT</code></li>
<li>出力イテレータの型を<code>Out</code></li>
<li>フォーマット引数の型を<code>T</code></li>
<li><code>f</code>を<code>F</code>のオブジェクト</li>
<li><code>cf</code>を<code>F</code>の<code>const</code>オブジェクト</li>
<li><code>u</code>を<code>T</code>のlvalue</li>
<li><code>t</code>を<code>T</code>または<code>const T</code>へ変換できる型のオブジェクト</li>
<li><code>PC</code>を<code><a href="basic_format_parse_context.html">basic_format_parse_context</a><charT></code></li>
<li><code>FC</code>を<code><a href="basic_format_context.html">basic_format_context</a><Out, charT></code></li>
<li><code>pc</code>を<code>PC</code>のlvalue</li>
<li><code>fc</code>を<code>FC</code>のlvalue</li>
</ul>
<p>ただし、<code><a href="formatter/parse.html">parse</a></code>の呼び出し前の状態で、<code>pc.begin()</code>は書式文字列中の対応する置換フィールドのオプションの先頭を指す。</p>
<ul>
<li>オプションが空でなければ、<code>*pc.begin()</code>は<code>:</code>の次の文字</li>
<li>オプションが空なら、<code>pc.begin() == pc.end()</code>または<code>*pc.begin() == '}'</code>である</li>
</ul>
<p><code><a href="formattable.html">std::formattable</a></code>コンセプトも参照。</p>
<p>フォーマッターは、書式文字列中に置換フィールドが見つかるたびに次のコードと近い形で呼び出される。</p>
<p><div class="codehilite"><pre><span></span><code><span class="k">typename</span><span class="w"> </span><span class="nc">FC</span><span class="o">::</span><span class="k">template</span><span class="w"> </span><span class="n">formatter_type</span><span class="o"><</span><span class="n">T</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="p">;</span>
<span class="n"><a href="basic_format_parse_context/advance_to.html">pc.advance_to</a></span><span class="p">(</span><span class="n"><a href="formatter/parse.html">f.parse</a></span><span class="p">(</span><span class="n">pc</span><span class="p">));</span><span class="w"> </span><span class="c1">// オプションを解析し状態を保存する</span>
<span class="n"><a href="basic_format_context/advance_to.html">fc.advance_to</a></span><span class="p">(</span><span class="n"><a href="formatter/format.html">f.format</a></span><span class="p">(</span><span class="n">u</span><span class="p">,</span><span class="w"> </span><span class="n">fc</span><span class="p">));</span><span class="w"> </span><span class="c1">// 状態をもとにフォーマットを行う</span>
</code></pre></div>
</p>
<p><a href="basic_format_arg/handle.html">handle</a>も参照。</p>
<h2>メンバ関数</h2>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>メンバ関数</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="formatter/parse.html">parse</a></code></td>
<td>書式の解析を行う</td>
<td>C++20</td>
</tr>
<tr>
<td><code><a href="formatter/format.html">format</a></code></td>
<td>書式化を行う</td>
<td>C++20</td>
</tr>
</tbody>
</table>
<h3>文字・文字列に対する特殊化</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>メンバ関数</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="formatter/set_debug_format.html">set_debug_format</a></code></td>
<td>デバッグ出力を有効にする</td>
<td>C++23</td>
</tr>
</tbody>
</table>
<h3>pair / tuple向けの特殊化</h3>
<table border="1" bordercolor="#888" style="border-collapse:collapse">
<thead>
<tr>
<th>メンバ関数</th>
<th>説明</th>
<th>対応バージョン</th>
</tr>
</thead>
<tbody>
<tr>
<td><code><a href="formatter/set_separator.html">set_separator</a></code></td>
<td>要素の区切り文字を設定する</td>
<td>C++23</td>
</tr>
<tr>
<td><code><a href="formatter/set_brackets.html">set_brackets</a></code></td>
<td>全体の囲み文字を設定する</td>
<td>C++23</td>
</tr>
</tbody>
</table>
<h2>例</h2>
<h3>オリジナル書式なし、型変換のみの場合</h3>
<p><div class="yata" id="f0f1f0a4ab5ebbae12a3bb9c2578b97179eb8305"><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="k">enum</span><span class="w"> </span><span class="nc">color</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">red</span><span class="p">,</span><span class="w"> </span><span class="n">green</span><span class="p">,</span><span class="w"> </span><span class="n">blue</span><span class="w"> </span><span class="p">};</span>
<span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">color_names</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="s">"red"</span><span class="p">,</span><span class="w"> </span><span class="s">"green"</span><span class="p">,</span><span class="w"> </span><span class="s">"blue"</span><span class="w"> </span><span class="p">};</span>
<span class="k">template</span><span class="o"><></span>
<span class="k">struct</span><span class="w"> </span><span class="nc">std</span><span class="o">::</span><span class="n">formatter</span><span class="o"><</span><span class="n">color</span><span class="o">></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">formatter</span><span class="o"><</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">format</span><span class="p">(</span><span class="n">color</span><span class="w"> </span><span class="n">c</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="basic_format_context.html">std::format_context</a></span><span class="o">&</span><span class="w"> </span><span class="n">ctx</span><span class="p">)</span><span class="w"> </span><span class="k">const</span><span class="w"> </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">formatter</span><span class="o"><</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*>::</span><span class="n">format</span><span class="p">(</span><span class="n">color_names</span><span class="p">[</span><span class="n">c</span><span class="p">],</span><span class="w"> </span><span class="n">ctx</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<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"><a href="format.html">std::format</a></span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="n">red</span><span class="p">)</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>
<h4>出力</h4>
<p><pre><code>red
</code></pre></p>
<h3>オリジナル書式を定義する例</h3>
<p><div class="yata" id="795293b1e8ac834d0cb3e053df1bcc3f84ab3a64"><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="k">enum</span><span class="w"> </span><span class="nc">color</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">red</span><span class="p">,</span><span class="w"> </span><span class="n">green</span><span class="p">,</span><span class="w"> </span><span class="n">blue</span><span class="w"> </span><span class="p">};</span>
<span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">color_names</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="s">"red"</span><span class="p">,</span><span class="w"> </span><span class="s">"green"</span><span class="p">,</span><span class="w"> </span><span class="s">"blue"</span><span class="w"> </span><span class="p">};</span>
<span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">jp_color_names</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="s">"赤"</span><span class="p">,</span><span class="w"> </span><span class="s">"緑"</span><span class="p">,</span><span class="w"> </span><span class="s">"青"</span><span class="w"> </span><span class="p">};</span>
<span class="k">template</span><span class="o"><></span>
<span class="k">struct</span><span class="w"> </span><span class="nc">std</span><span class="o">::</span><span class="n">formatter</span><span class="o"><</span><span class="n">color</span><span class="o">></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">is_jp</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="c1">// コンパイル時の書式文字列の解析があるため、</span>
<span class="w"> </span><span class="c1">// constexprにする必要がある。</span>
<span class="w"> </span><span class="c1">// この関数に渡されるパラメータは、{:%j}の%以降。</span>
<span class="w"> </span><span class="c1">// 解析がおわった場所を指すイテレータを返す。</span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">parse</span><span class="p">(</span><span class="n"><a href="basic_format_parse_context.html">std::format_parse_context</a></span><span class="o">&</span><span class="w"> </span><span class="n">ctx</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">it</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="basic_format_parse_context/begin.html">ctx.begin()</a></span><span class="p">;</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">it</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="p">{</span>
<span class="w"> </span><span class="o">++</span><span class="n">it</span><span class="p">;</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">it</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">'j'</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">is_jp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">it</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">'e'</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">is_jp</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="p">}</span>
<span class="w"> </span><span class="o">++</span><span class="n">it</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">it</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">// format()関数は書式の情報をもたない。</span>
<span class="w"> </span><span class="c1">// parse()関数で解析した書式をメンバ変数で保持しておいて、</span>
<span class="w"> </span><span class="c1">// それをもとに書式化する</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">format</span><span class="p">(</span><span class="n">color</span><span class="w"> </span><span class="n">c</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="basic_format_context.html">std::format_context</a></span><span class="o">&</span><span class="w"> </span><span class="n">ctx</span><span class="p">)</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n"><a href="format_to.html">std::format_to</a></span><span class="p">(</span><span class="n"><a href="basic_format_context/out.html">ctx.out()</a></span><span class="p">,</span><span class="w"> </span><span class="s">"{}"</span><span class="p">,</span>
<span class="w"> </span><span class="n">is_jp</span><span class="w"> </span><span class="o">?</span><span class="w"> </span><span class="n">jp_color_names</span><span class="p">[</span><span class="n">c</span><span class="p">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">color_names</span><span class="p">[</span><span class="n">c</span><span class="p">]</span>
<span class="w"> </span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<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"><a href="format.html">std::format</a></span><span class="p">(</span><span class="s">"{:%j} {:%e}"</span><span class="p">,</span><span class="w"> </span><span class="n">red</span><span class="p">,</span><span class="w"> </span><span class="n">blue</span><span class="p">)</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>
<h4>出力</h4>
<p><pre><code>赤 blue
</code></pre></p>
<h3>複数のメンバ変数を含むクラスの場合</h3>
<p><div class="yata" id="d25188a377882c9f6e282ac92bd1f5a4bd0c3fe9"><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="k">struct</span><span class="w"> </span><span class="nc">Point</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">y</span><span class="p">;</span>
<span class="p">};</span>
<span class="k">template</span><span class="o"><></span>
<span class="k">struct</span><span class="w"> </span><span class="nc">std</span><span class="o">::</span><span class="n">formatter</span><span class="o"><</span><span class="n">Point</span><span class="o">></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">formatter</span><span class="o"><</span><span class="n"><a href="../string/basic_string.html">std::string</a></span><span class="o">></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">format</span><span class="p">(</span><span class="n">Point</span><span class="w"> </span><span class="n">p</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="basic_format_context.html">std::format_context</a></span><span class="o">&</span><span class="w"> </span><span class="n">ctx</span><span class="p">)</span><span class="w"> </span><span class="k">const</span><span class="w"> </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">formatter</span><span class="o"><</span><span class="n"><a href="../string/basic_string.html">std::string</a></span><span class="o">>::</span><span class="n">format</span><span class="p">(</span>
<span class="w"> </span><span class="n"><a href="format.html">std::format</a></span><span class="p">(</span><span class="s">"[{}, {}]"</span><span class="p">,</span><span class="w"> </span><span class="n">p</span><span class="p">.</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">p</span><span class="p">.</span><span class="n">y</span><span class="p">),</span>
<span class="w"> </span><span class="n">ctx</span><span class="p">);</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<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"><a href="format.html">std::format</a></span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="n">Point</span><span class="p">{</span><span class="mf">1.2f</span><span class="p">,</span><span class="w"> </span><span class="mf">3.4f</span><span class="p">})</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>
<h4>出力</h4>
<p><pre><code>[1.2, 3.4]
</code></pre></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 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#gcc">GCC</a>: 13 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: 2022 Update 2 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
</ul>
<h2>関連項目</h2>
<ul>
<li><code><a href="../vector/vector.html">vector<bool></a></code></li>
</ul>
<h2>参照</h2>
<ul>
<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://github.com/fmtlib/fmt" target="_blank">{fmt}</a></li>
<li><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2286r8.html" target="_blank">P2286R8 Formatting Ranges</a></li>
<li><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2585r1.html" target="_blank">P2585R1 Improve default container formatting</a><ul>
<li>C++23から、Range・コンテナ、<code>pair</code>、<code>tuple</code>のフォーマット出力、および文字・文字列のデバッグ指定 (<code>"?"</code>) が追加された</li>
</ul>
</li>
</ul></div>
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