236 lines
12 KiB
HTML
236 lines
12 KiB
HTML
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<title>std::basic_format_context</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_format_basic_format_context 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>basic_format_context</h1>
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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>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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<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="kw1">class</span> CharT<span class="sy1">></span><br />
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<span class="kw1">class</span> basic_format_context<span class="sy4">;</span></span></div>
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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">using</span> format_context <span class="sy1">=</span> basic_format_context<span class="sy1"><</span><span class="coMULTI">/* unspecified */</span>, <span class="kw4">char</span><span class="sy1">></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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">using</span> wformat_context <span class="sy1">=</span> basic_format_context<span class="sy1"><</span><span class="coMULTI">/* unspecified */</span>, <span class="kw4">wchar_t</span><span class="sy1">></span><span class="sy4">;</span></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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<td></td>
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<p>提供到由格式化参数和输出迭代器组成的格式化状态的访问。</p>
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<p>若 <code>OutputIt</code> 不实现 <code>std::output_iterator<const CharT&></code> 则行为未定义。</p>
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<div class="t-li1"><span class="t-li">2)</span> 未指明的模板实参是后附到 <span class="t-lc"><a href="cpp-string-basic_string.html">std::string</a></span> 的输出迭代器，例如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-back_insert_iterator.html"><span class="kw660">std::<span class="me2">back_insert_iterator</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span></span></span> 。鼓励实现使用到支持后附到任何连续存储且大小可变的容器的类型擦除缓冲。</div>
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<div class="t-li1"><span class="t-li">3)</span> 未指明的模板实参是后附到 <span class="t-lc"><a href="cpp-string-basic_string.html">std::wstring</a></span> 的输出迭代器。</div>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>类型</td>
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<td>定义</td>
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<td><code>iterator</code></td>
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<td><code>OutputIt</code></td>
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<td><code>char_type</code></td>
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<td><code>CharT</code></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.88.AB.E5.90.8D.E6.A8.A1.E7.89.88">成员别名模版</span></h3>
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<td>类型</td>
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<td>定义</td>
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<td><code>formatter_type<T></code></td>
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<td><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>T, CharT<span class="sy1">></span></span></span></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<div><span class="t-lines"><span>arg</span></span></div>
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<td>返回位于给定下标的参数<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>locale</span></span></div>
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</td>
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<td>返回用于本地环境特定格式化的本地环境<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>out</span></span></div>
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<td>返回指向输出缓冲区的迭代器<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>advance_to</span></span></div>
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</td>
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<td>推进输出迭代器到给定位置<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h2><span class="mw-headline" id="std::basic_format_context::arg"><span style="font-size:0.7em; line-height:130%">std::basic_format_context::</span>arg</span></h2>
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<div><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">basic_format_arg</span><span class="sy1"><</span>basic_format_context<span class="sy1">></span> arg<span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> id<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<p>返回保有 <code>args</code> 中第 <code>id</code> 元素的 <code>std::basic_format_arg</code> ，其中 <code>args</code> 是参数包或传递给格式化函数的 <code>std::basic_format_args</code> 对象。</p>
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<p>若 <code>id</code> 不小于格式化参数的数量，则返回默认构造的 <code>std::basic_format_arg</code> （保有一个 <span class="t-lc"><a href="cpp-utility-variant-monostate.html">std::monostate</a></span> 对象）。</p>
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<h2><span class="mw-headline" id="std::basic_format_context::locale"><span style="font-size:0.7em; line-height:130%">std::basic_format_context::</span>locale</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a> locale<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>返回传递给格式化函数的本地环境，或若格式化函数不接收本地环境返回默认构造的 <span class="t-lc"><a href="cpp-locale-locale.html">std::locale</a></span> 。</p>
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<h2><span class="mw-headline" id="std::basic_format_context::out"><span style="font-size:0.7em; line-height:130%">std::basic_format_context::</span>out</span></h2>
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<div><span class="mw-geshi cpp source-cpp">iterator out<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>返回指向输出缓冲区的迭代器。从存储的迭代器移动构造结果。</p>
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<h2><span class="mw-headline" id="std::basic_format_context::advance_to"><span style="font-size:0.7em; line-height:130%">std::basic_format_context::</span>advance_to</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> advance_to<span class="br0">(</span>iterator it<span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>移动赋值 <code>it</code> 给存储的输出迭代器。调用 <code>advance_to</code> 后，对 <code>out()</code> 的后继调用将返回 <code>it</code> 的副本。</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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<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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<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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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3567">LWG 3567</a></td>
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<td>C++20</td>
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<td><code>basic_format_context</code> 无法用于仅移动的迭代器类型</td>
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<td>使之移动迭代器</td>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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