96 lines
8.3 KiB
HTML
96 lines
8.3 KiB
HTML
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<title>std::c8rtomb</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_c8rtomb 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>c8rtomb</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-string.html">string</a>‎ | <a href="cpp-string-multibyte.html">multibyte</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-cuchar.html"><cuchar></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> c8rtomb<span class="br0">(</span> <span class="kw4">char</span><span class="sy2">*</span> s, char8_t c8, <a href="cpp-string-multibyte-mbstate_t.html"><span class="kw1179">std::<span class="me2">mbstate_t</span></span></a><span class="sy2">*</span> ps <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>转换来自 UTF-8 的单个编码点为窄多字节字符表示。</p>
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<p>若 <code>s</code> 不是空指针且 <code>c8</code> 是编码点的合法 UTF-8 编码中的最后编码单元，则函数确定存储该编码点的多字节字符表示所需的字符数（包含任何迁移序列，并且考虑到当前多字节转换状态 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> ），并存储多字节字符表示于首元素为 <code>s</code> 所指向的字符数组，按需更新 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 。此函数至多能写入 <span class="t-lc">MB_CUR_MAX</span> 个字节。</p>
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<p>若 <code>c8</code> 不是编码点表示中的最终 UTF-8 编码单元，则函数不写入 <code>s</code> 所指向的数组，只更新 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 。</p>
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<p>若 <code>s</code> 为空指针，则调用等价于对某内部缓冲区 <code>buf</code> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">c8rtomb</span><span class="br0">(</span>buf, u8<span class="st0">'<span class="es5">\0</span>'</span>, ps<span class="br0">)</span></span></span> 。</p>
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<p>若 <code>c8</code> 为空字符 <span class="t-c"><span class="mw-geshi cpp source-cpp">u8<span class="st0">'<span class="es5">\0</span>'</span></span></span> ，则存储空字节，前附任何恢复初始迁移状态所需的迁移序列，并更新转换状态参数 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> ，使之代表初始迁移状态。</p>
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<p>此函数所用的多字节编码由当前活跃的 C 本地环境指定。</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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<td>s</td>
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<td>-</td>
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<td>指向将要存储多字节字符的通常字符数组的指针</td>
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<td>c8</td>
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<td>-</td>
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<td>要转换的 UTF-8 编码单元</td>
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<tr class="t-par">
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<td>ps</td>
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<td>-</td>
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<td>指向转译多字节字符串时使用的转换状态的指针</td>
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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>存储于数组中的的字节数（包含任何迁移序列）。 <span class="t-c"><span class="mw-geshi cpp source-cpp">c8</span></span> 不是编码点的 UTF-8 表示中的最终编码单元时，可以为零。</p>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">c8</span></span> 非法（不贡献到对应合法多字节字符的 <span class="t-c"><span class="mw-geshi cpp source-cpp">char8_t</span></span> 序列），则存储宏 <span class="t-lc"><a href="cpp-error-errno_macros.html">EILSEQ</a></span> 的值于 <span class="t-lc"><a href="cpp-error-errno.html">errno</a></span> ，返回 <code>size_t(-1)</code> ，而转换状态未指定。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>以空指针参数 <span class="t-c"><span class="mw-geshi cpp source-cpp">s</span></span> 调用 <code>c8rtomb</code> ，可能会与其他以空指针参数 <span class="t-c"><span class="mw-geshi cpp source-cpp">s</span></span> 对 <code>c8rtomb</code> 的调用造成数据竞争。</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=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div><a href="cpp-string-multibyte-mbrtoc8.html"><span class="t-lines"><span>mbrtoc8</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>转换窄多字节字符为 UTF-8 编码<br />
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<span class="t-mark">(函数)</span></td>
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