150 lines
13 KiB
HTML
150 lines
13 KiB
HTML
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<title>std::vformat_to</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_format_vformat_to skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>vformat_to</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-format.html">format</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<div>定义于头文件 <code><a href="cpp-header-format.html"><format></a></code></div>
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<td></td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> OutputIt <span class="sy1">></span><br />
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OutputIt vformat_to<span class="br0">(</span> OutputIt out, <a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> fmt, std<span class="sy4">::</span><span class="me2">format_args</span> args <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> OutputIt <span class="sy1">></span><br />
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OutputIt vformat_to<span class="br0">(</span> OutputIt out, <a href="cpp-string-basic_string_view.html"><span class="kw1250">std::<span class="me2">wstring_view</span></span></a> fmt, std<span class="sy4">::</span><span class="me2">wformat_args</span> args <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> OutputIt <span class="sy1">></span><br /></span>
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<p>OutputIt vformat_to<span class="br0">(</span> OutputIt out, <span class="kw4">const</span> <a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="sy3">&</span> loc,<br /></p>
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<a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> fmt, std<span class="sy4">::</span><span class="me2">format_args</span> args <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx20">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> OutputIt <span class="sy1">></span><br /></span>
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<p>OutputIt vformat_to<span class="br0">(</span> OutputIt out, <span class="kw4">const</span> <a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="sy3">&</span> loc,<br /></p>
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<a href="cpp-string-basic_string_view.html"><span class="kw1250">std::<span class="me2">wstring_view</span></span></a> fmt, std<span class="sy4">::</span><span class="me2">wformat_args</span> args <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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<p>按照格式字符串 <code>fmt</code> 格式化 <code>args</code> ，并写结果到输出迭代器 <code>out</code> 。 <code>loc</code> 若存在则用于本地环境特定的格式化。</p>
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<p>令 <code>CharT</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp">decltype<span class="br0">(</span>fmt<span class="br0">)</span><span class="sy4">::</span><span class="me2">char_type</span></span></span> （对重载 <span class="t-v">(1,3)</span> 为 <code>char</code> ，对重载 <code>wchar_t</code> 为 <span class="t-v">(2,4)</span> ）。</p>
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<p>这些重载仅若 <code>OutputIt</code> 满足概念 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">output_iterator</span><span class="sy1"><</span><span class="kw4">const</span> CharT<span class="sy3">&</span><span class="sy1">></span></span></span> 才参与重载决议。若 <code>OutputIt</code> 不实现（满足其语义要求）概念 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">output_iterator</span><span class="sy1"><</span><span class="kw4">const</span> CharT<span class="sy3">&</span><span class="sy1">></span></span></span> ，或若对 <code>Args</code> 中任何 <code>Ti</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">formatter</span><span class="sy1"><</span>Ti, CharT<span class="sy1">></span></span></span> 不满足<a href="cpp-named_req-Formatter.html"><span style="font-style:italic">格式化器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Formatter)</span></a> 要求则行为未定义。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>out</td>
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<td>-</td>
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<td>指向输出缓冲区的迭代器</td>
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</tr>
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<tr class="t-par">
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<td>fmt</td>
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<td>-</td>
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<td>
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<div class="t-template-editlink" style=""></div>
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表示格式字符串的字符串视图。格式字符串由以下内容组成：
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<ul>
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<li>通常字符（除了 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">{</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">}</span></span></span> ），它们被不加修改地复制到输出，</li>
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<li>转义序列 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">{</span><span class="br0">{</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">}</span><span class="br0">}</span></span></span> ，它们在输出中被分别替换成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">{</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">}</span></span></span> ，以及</li>
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<li>替换域。</li>
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</ul>
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<p>每个替换域拥有下列格式：</p>
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<ul>
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<li>引入的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">{</span></span></span> 字符；</li>
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<li><span class="t-mark">(可选)</span> <span class="t-spar">arg-id</span> ，一个非负数；</li>
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<li><span class="t-mark">(可选)</span> 冒号（ <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy4">:</span></span></span> ）后随格式说明；</li>
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<li>终止的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">}</span></span></span> 字符。</li>
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</ul>
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<p><span class="t-spar">arg-id</span> 指定用于格式化其值的 <code>args</code> 中的参数的下标；若省略 <span class="t-spar">arg-id</span> ，则按顺序使用参数。格式字符串中的 <span class="t-spar">arg-id</span> 必须全部存在或全部被省略。混合手动和自动指定下标是错误。</p>
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<p>格式说明由对应参数特化的 <span class="t-lc">std::formatter</span> 定义。</p>
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<ul>
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<li>对于基本类型和标准字符串类型，格式说明为<a href="cpp-utility-format-formatter.html#.E6.A0.87.E5.87.86.E6.A0.BC.E5.BC.8F.E8.AF.B4.E6.98.8E">标准格式说明</a>；</li>
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<li>对于标准日期和时间类型，格式说明为 <a href="cpp-chrono-system_clock-formatter.html#.E6.A0.BC.E5.BC.8F.E8.AF.B4.E6.98.8E">chrono 格式说明</a>；</li>
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<li>对于用户定义类型，格式说明由用户定义的 <span class="t-lc">std::formatter</span> 特化决定。</li>
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</ul>
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</td>
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</tr>
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<tr class="t-par">
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<td>args...</td>
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<td>-</td>
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<td>要格式化的参数</td>
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</tr>
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<tr class="t-par">
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<td>loc</td>
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<td>-</td>
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<td>用于本地环境特定的格式化的 <span class="t-lc"><a href="cpp-locale-locale.html">std::locale</a></span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>输出范围末尾后一位置的迭代器。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>若 <code>fmt</code> 对于提供的参数不是合法的格式字符串则抛出 <span class="t-lc">std::format_error</span> 。并且会传播格式化器或迭代器操作所抛的任何异常。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<tr>
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<td class="mbox-empty-cell"></td>
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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P2216R3">P2216R3</a></td>
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<td>C++20</td>
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<td><code>args</code> 的类型在 <code>OutputIt</code> 上参数化</td>
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<td>不参数化</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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</div>
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<div class="visualClear"></div>
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</div>
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