92 lines
9.8 KiB
HTML
92 lines
9.8 KiB
HTML
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<title>C++ 具名要求：格式化器 (Formatter)</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">C++ 具名要求：</span><span style="font-style:italic">格式化器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Formatter)</span></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-named_req.html">named req</a></span></div>
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<p><strong class="selflink"><span style="font-style:italic">格式化器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Formatter)</span></strong> 是对给定的格式化实参类型与字符类型抽象化格式化操作的类型。要求 <span class="t-lc">std::formatter</span> 的特化实现<span style="font-style:italic">格式化器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Formatter)</span> 。</p>
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<h3><span class="mw-headline" id=".E8.A6.81.E6.B1.82">要求</span></h3>
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<p>一个类型满足<span style="font-style:italic">格式化器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Formatter)</span> ，若它为半正则，意思是它满足：</p>
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<ul>
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<li><a href="cpp-named_req-DefaultConstructible.html"><span style="font-style:italic">可默认构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(DefaultConstructible)</span></a></li>
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<li><a href="cpp-named_req-CopyConstructible.html"><span style="font-style:italic">可复制构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyConstructible)</span></a></li>
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<li><a href="cpp-named_req-CopyAssignable.html"><span style="font-style:italic">可复制赋值</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyAssignable)</span></a></li>
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<li><a href="cpp-named_req-Destructible.html"><span style="font-style:italic">可析构</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Destructible)</span></a></li>
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<li><a href="cpp-named_req-Swappable.html"><span style="font-style:italic">可交换</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Swappable)</span></a></li>
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</ul>
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<p>而且给定</p>
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<ul>
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<li><code>Arg</code> ，格式化实参类型</li>
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<li><code>CharT</code> ，字符类型</li>
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<li><code>Formatter</code> ，对于类型 <code>Arg</code> 与 <code>CharT</code> 的<span style="font-style:italic">格式化器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Formatter)</span> 类型</li>
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<li><code>OutputIt</code> ，<a href="cpp-named_req-OutputIterator.html"><span style="font-style:italic">老式输出迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyOutputIterator)</span></a> 类型</li>
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<li><code>formatter</code> ， <code>Formatter</code> 类型值</li>
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<li><code>arg</code> ， <code>Arg</code> 类型左值</li>
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<li><code>t</code> ，可转换到（可能为 const ）的 <code>Arg</code></li>
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<li><code>ParseContext</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">basic_format_parse_context</span><span class="sy1"><</span>CharT<span class="sy1">></span></span></span> 的别名</li>
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<li><code>FormatContext</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">basic_format_context</span><span class="sy1"><</span>OutputIt, CharT<span class="sy1">></span></span></span> 的别名</li>
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<li><code>parse_context</code> ， <code>ParseContext</code> 类型左值</li>
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<li><code>format_context</code> ， <code>FormatContext</code> 类型左值</li>
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</ul>
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<table class="wikitable">
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<tr>
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<th>表达式</th>
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<th>返回类型</th>
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<th>语义</th>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">formatter.<span class="me1">parse</span><span class="br0">(</span>parse_context<span class="br0">)</span></span></span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">ParseContext<span class="sy4">::</span><span class="me2">iterator</span></span></span></td>
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<td>
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<ul>
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<li>对类型 <code>Arg</code> 分析 <span class="t-spar">格式说明</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span>parse_context.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, parse_context.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> ，直至首个未匹配的字符。</li>
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<li>抛出 <span class="t-lc">std::format_error</span> ，除非可分析整个范围或首个未匹配字符是 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">}</span></span></span> 。<sup id="cite_ref-1" class="reference"><a href="cpp-named_req-Formatter.html#cite_note-1">[注 1]</a></sup></li>
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<li>存储分析的格式说明符到 <code>formatter</code> 中并返回已分析范围的尾迭代器。</li>
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</ul>
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</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">formatter.<span class="me1">format</span><span class="br0">(</span>t, format_context<span class="br0">)</span></span></span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">FormatContext<span class="sy4">::</span>​iterator</span></span></td>
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<td>
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<ul>
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<li>按存储于 <code>formatter</code> 的格式说明符分析 <code>t</code> ，写输出到 <span class="t-c"><span class="mw-geshi cpp source-cpp">format_context.<span class="me1">out</span><span class="br0">(</span><span class="br0">)</span></span></span> 并返回输出范围的尾迭代器。</li>
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<li>输出应当仅依赖
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<ul>
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<li><code>t</code>、</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">format_context.<span class="me1">locale</span><span class="br0">(</span><span class="br0">)</span></span></span>、</li>
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<li>来自前一次调用的范围 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span>parse_context.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, parse_context.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> ，以及</li>
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<li>对于任何 <span class="t-lc"><a href="cpp-types-size_t.html">std::size_t</a></span> 类型值 <code>n</code> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">format_context.<span class="me1">arg</span><span class="br0">(</span>n<span class="br0">)</span></span></span> 。</li>
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</ul>
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</li>
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</ul>
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</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">formatter.<span class="me1">format</span><span class="br0">(</span>arg, format_context<span class="br0">)</span></span></span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">FormatContext<span class="sy4">::</span>​iterator</span></span></td>
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<td>
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<p>同上，但不修改 <code>arg</code> 。</p>
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</td>
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</tr>
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</table>
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<ol class="references">
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<li id="cite_note-1"><span class="mw-cite-backlink"><a href="cpp-named_req-Formatter.html#cite_ref-1">↑</a></span> <span class="reference-text">这允许格式化器放出有意义的错误消息。</span></li>
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</ol>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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