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web/cppreference-zh/chmhelp/cpp-string-multibyte-mbrtowc.html
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web/cppreference-zh/chmhelp/cpp-string-multibyte-mbrtowc.html
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<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::mbrtowc</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_mbrtowc skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>mbrtowc</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-string.html">string</a>‎ | <a href="cpp-string-multibyte.html">multibyte</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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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-cwchar.html"><cwchar></a></code></div>
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</td>
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<td></td>
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<td></td>
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</tr>
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<tr class="t-dcl">
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<td class="t-dcl-nopad">
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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> mbrtowc<span class="br0">(</span> <span class="kw4">wchar_t</span><span class="sy2">*</span> pwc,<br /></span>
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<p> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> s,<br />
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<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> n,<br /></p>
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<a href="cpp-string-multibyte-mbstate_t.html"><span class="kw1178">std::<span class="me2">mbstate_t</span></span></a><span class="sy2">*</span> ps <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td class="t-dcl-nopad"></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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</tr>
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</tbody>
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</table>
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<p>转换窄多字节字符为宽字符。</p>
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<p>若 <code>s</code> 不是空指针，则从 <code>s</code> 所指向的字节起，审查多字节字符串的至多 <code>n</code> 个字节，以确定完成下个多字节字符（包含任何迁移序列）的字节数。若该函数确定 <code>s</code> 的下个多字节字符完整且合法，则将它转换为对应的宽字符，并存储之于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>pwc</span></span> （若 <code>pwc</code> 非空）。</p>
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<p>若 <code>s</code> 是空指针，则忽略 <code>n</code> 和 <code>pwc</code> 的值，而调用等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">mbrtowc</span><span class="br0">(</span><a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a>, <span class="st0">""</span>, <span class="nu0">1</span>, ps<span class="br0">)</span></span></span> 。</p>
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<p>若产生的宽字符是空字符，则存储于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 的转换状态为初始迁移状态。</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>pwc</td>
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<td>-</td>
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<td>指向要写入结果宽字符位置的指针</td>
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</tr>
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<tr class="t-par">
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<td>s</td>
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<td>-</td>
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<td>指向用作输入的多字节字符串的指针</td>
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</tr>
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<tr class="t-par">
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<td>n</td>
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<td>-</td>
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<td><code>s</code> 中能被检验的字节数限制</td>
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</tr>
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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的转换状态的指针</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>下列首个可应用者：</p>
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<ul>
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<li>若转换自 <code>s</code> 的字符为空字符，则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> （若 <span class="t-c"><span class="mw-geshi cpp source-cpp">pwc</span></span> 非空则存储于 <code>*pwc</code> ）</li>
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<li>成功地 <code>s</code> 从转换的多字节字符 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="nu0">1</span>...<span class="me1">n</span><span class="br0">]</span></span></span> 的字节数</li>
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<li>若接下来的 <code>n</code> 字节组成不完整，但该部分合法的宽字符，则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="sy2">-</span><span class="nu0">2</span><span class="br0">)</span></span></span> 。不写入 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>pwc</span></span> 。</li>
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<li>若出现编码错误则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span></span></span> 。不写入 <code>*pwc</code> ，存储值 <span class="t-lc"><a href="cpp-error-errno_macros.html">EILSEQ</a></span> 于 <span class="t-lc"><a href="cpp-error-errno.html">errno</a></span> ，并且置 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 的值为未指定。</li>
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</ul>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <clocale></span>
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<span class="co2">#include <cstring></span>
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<span class="co2">#include <cwchar></span>
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<span class="kw4">void</span> print_mb<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> ptr<span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-string-multibyte-mbstate_t.html"><span class="kw1178">std::<span class="me2">mbstate_t</span></span></a> state <span class="sy1">=</span> <a href="cpp-string-multibyte-mbstate_t.html"><span class="kw1178">std::<span class="me2">mbstate_t</span></span></a><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 初始状态</span>
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<span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> end <span class="sy1">=</span> ptr <span class="sy2">+</span> <a href="cpp-string-byte-strlen.html"><span class="kw1145">std::<span class="me2">strlen</span></span></a><span class="br0">(</span>ptr<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> len<span class="sy4">;</span>
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<span class="kw4">wchar_t</span> wc<span class="sy4">;</span>
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<span class="kw1">while</span><span class="br0">(</span><span class="br0">(</span>len <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">mbrtowc</span><span class="br0">(</span><span class="sy3">&</span>wc, ptr, end<span class="sy2">-</span>ptr, <span class="sy3">&</span>state<span class="br0">)</span><span class="br0">)</span> <span class="sy1">></span> <span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Next "</span> <span class="sy1"><<</span> len <span class="sy1"><<</span> <span class="st0">" bytes are the character "</span> <span class="sy1"><<</span> wc <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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ptr <span class="sy2">+</span><span class="sy1">=</span> len<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-locale-setlocale.html"><span class="kw1989">std::<span class="me2">setlocale</span></span></a><span class="br0">(</span><a href="cpp-locale-LC_categories.html"><span class="kw1992">LC_ALL</span></a>, <span class="st0">"en_US.utf8"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// UTF-8 窄多字节编码</span>
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<span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> str <span class="sy1">=</span> u8<span class="st0">"z<span class="es3">\u00df</span><span class="es3">\u6c34</span><span class="es4">\U0001d10b</span>"</span><span class="sy4">;</span> <span class="co1">// 或 u8"zß水𝄋"</span>
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<span class="co1">// 或 "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";</span>
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print_mb<span class="br0">(</span>str<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">Next 1 bytes are the character z
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Next 2 bytes are the character ß
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Next 3 bytes are the character 水
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Next 4 bytes are the character 𝄋</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-mbtowc.html"><span class="t-lines"><span>mbtowc</span></span></a></div>
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</div>
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</td>
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<td>将下一个多字节字符转换成宽字符<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-wcrtomb.html"><span class="t-lines"><span>wcrtomb</span></span></a></div>
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</div>
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</td>
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<td>给定状态，转换宽字符到其多字节表示<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-locale-codecvt-in.html"><span class="t-lines"><span>do_in</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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</div>
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</td>
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<td>从 externT 转换字符串为 internT ，如在从文件读取时<br />
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<span class="t-mark">(<code>std::codecvt<InternT,ExternT,State></code> 的虚受保护成员函数)</span></td>
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</tr>
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</table>
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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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</html>
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