161 lines
18 KiB
HTML
161 lines
18 KiB
HTML
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<title>std::mbrtoc32</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_mbrtoc32 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>mbrtoc32</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>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> mbrtoc32<span class="br0">(</span> <span class="kw4">char32_t</span><span class="sy2">*</span> pc32,<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 class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>从窄多字符编码转换编码点到其 UTF-32 字符表示。</p>
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<p>若 <code>s</code> 不是空指针，则审查以 <code>s</code> 所指向的字节开始的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所需的字节数（包含任何迁移序列）。若函数确定 <code>s</code> 中下个多字节字符完整且合法，则将它转换成对应的 32 位宽字符并存储于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>pc32</span></span> （若 <code>pc32</code> 非空）。</p>
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<p>若 <code>*s</code> 中下个多字节字符对应多 char32_t 序列（对于 UTF-32 不可能），则在首次调用此函数后更新 <code>*ps</code> ，以满足下次到 <code>mbrtoc32</code> 的调用将写出附加的 char32_t ，而不考虑 <code>*s</code> 。</p>
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<p>若 <code>s</code> 是空指针，则忽略 <code>n</code> 与 <code>pc32</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">mbrtoc32</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，则转换状态 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 表示初始迁移状态。</p>
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<p>此函数所用的多字节编码为当前活跃的 C 本地环境所指定。</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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<table class="t-par-begin">
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<td>pc32</td>
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<td>-</td>
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<td>指向将写入产生的 32 位宽字符的位置的指针</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>s 中能检验的字节数上的限制</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所用的转换状态对象的指针</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>下列首个应用者：</p>
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<ul>
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<li>若从 <code>s</code> 转换的字符为空字符（并存储于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>pc32</span></span> 中，若它非空）则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 。</li>
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<li>成功从 <code>s</code> 转换的多字节字符的字节数 <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> 。</li>
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<li>若现已将来自多 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char32_t</span></span></span> 字符的下个 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char32_t</span></span></span> 写入 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>pc32</span></span> ，则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">3</span></span></span> 。此情况下不从输入处理字节。</li>
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<li>若接下来 <code>n</code> 个字节组成不完整，但到此仍合法的多字节字符则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">2</span></span></span> 。不写入内容到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>pc32</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="sy2">-</span><span class="nu0">1</span></span></span> 。不写入内容到 <code>*pc32</code> ，存储 <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> 且 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 的值未指定。</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 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 <iomanip></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="co2">#include <cuchar></span>
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<span class="co2">#include <cassert></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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<a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a> str <span class="sy1">=</span> u8<span class="st0">"z<span class="es3">\u00df</span><span class="es3">\u6c34</span><span class="es4">\U0001F34C</span>"</span><span class="sy4">;</span> <span class="co1">// 或 u8"zß水🍌"</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Processing "</span> <span class="sy1"><<</span> str.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" bytes: [ "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-showbase.html"><span class="kw1765">std::<span class="me2">showbase</span></span></a><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span> c<span class="sy4">:</span> str<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-hex.html"><span class="kw1781">std::<span class="me2">hex</span></span></a> <span class="sy1"><<</span> <span class="sy2">+</span>c <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"]<span class="es1">\n</span>"</span><span class="sy4">;</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="br0">{</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 零初始化为初始状态</span>
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<span class="kw4">char32_t</span> c32<span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>ptr <span class="sy1">=</span> str.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span>, <span class="sy2">*</span>end <span class="sy1">=</span> str.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> str.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> <span class="nu0">1</span><span class="sy4">;</span>
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<span class="kw1">while</span><span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> rc <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">mbrtoc32</span><span class="br0">(</span><span class="sy3">&</span>c32, ptr, end <span class="sy2">-</span> ptr, <span class="sy3">&</span>state<span class="br0">)</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Next UTF-32 char: "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-hex.html"><span class="kw1781">std::<span class="me2">hex</span></span></a> <span class="sy1"><<</span> c32 <span class="sy1"><<</span> <span class="st0">" obtained from "</span><span class="sy4">;</span>
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<a href="cpp-error-assert.html"><span class="kw774">assert</span></a><span class="br0">(</span>rc <span class="sy3">!</span><span class="sy1">=</span> <span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="br0">)</span><span class="sy2">-</span><span class="nu0">3</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// no surrogates in UTF-32</span>
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<span class="kw1">if</span><span class="br0">(</span>rc <span class="sy1"><=</span> <span class="br0">(</span><span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="br0">)</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span> <span class="sy2">/</span> <span class="nu0">2</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-hex.html"><span class="kw1780">std::<span class="me2">dec</span></span></a> <span class="sy1"><<</span> rc <span class="sy1"><<</span> <span class="st0">" bytes [ "</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> n <span class="sy1"><</span> rc<span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-hex.html"><span class="kw1781">std::<span class="me2">hex</span></span></a> <span class="sy1"><<</span> <span class="sy2">+</span><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="br0">)</span>ptr<span class="br0">[</span>n<span class="br0">]</span> <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <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> rc<span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="kw1">break</span><span class="sy4">;</span>
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<span class="br0">}</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">Processing 10 bytes: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c ]
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Next UTF-32 char: 0x7a obtained from 1 bytes [ 0x7a ]
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Next UTF-32 char: 0xdf obtained from 2 bytes [ 0xc3 0x9f ]
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Next UTF-32 char: 0x6c34 obtained from 3 bytes [ 0xe6 0xb0 0xb4 ]
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Next UTF-32 char: 0x1f34c obtained from 4 bytes [ 0xf0 0x9f 0x8d 0x8c ]</pre></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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<div class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-c32rtomb.html"><span class="t-lines"><span>c32rtomb</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>转换 32 位宽字符为窄多字节字符串<br />
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<span class="t-mark">(函数)</span></td>
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<tr class="t-dsc">
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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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<div class="visualClear"></div>
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