207 lines
15 KiB
HTML
207 lines
15 KiB
HTML
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<title>wctomb, wctomb_s</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_string_multibyte_wctomb skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading">wctomb, wctomb_s</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-string.html">string</a>‎ | <a href="c-string-multibyte.html">multibyte</a></span></div>
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<div>定义于头文件 <code><stdlib.h></code></div>
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<td></td>
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<div><span class="mw-geshi c source-c"><span class="kw4">int</span> wctomb<span class="br0">(</span> <span class="kw4">char</span> <span class="sy2">*</span>s, <span class="kw4">wchar_t</span> wc <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl t-since-c11">
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<div><span class="mw-geshi c source-c">errno_t wctomb_s<span class="br0">(</span><span class="kw4">int</span> <span class="sy2">*</span><span class="kw4">restrict</span> status, <span class="kw4">char</span> <span class="sy2">*</span><span class="kw4">restrict</span> s, rsize_t ssz, <span class="kw4">wchar_t</span> wc<span class="br0">)</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-c11">(C11 起)</span></td>
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<td></td>
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<div class="t-li1"><span class="t-li">1)</span> 转换宽字符 <code>wc</code> 为多字节编码，并存储之（含迁移状态）于 <code>s</code> 指向其首元素的字符数组。存储字节数不多于 <span class="t-c"><span class="mw-geshi c source-c">MB_CUR_MAX</span></span> 。</div>
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<div class="t-li1"><span class="t-li"></span> 若 <code>wc</code> 是空字符，则将空字符写入 <code>s</code> ，之前可以有需要恢复初始迁移状态的任何迁移状态。</div>
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<div class="t-li1"><span class="t-li"></span> 若 <code>s</code> 是空指针，则此函数重设全局转换状态并确定是否使用迁移序列。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，除了结果被返回到输出参数 <code>status</code> ，在运行时检测下列错误，并调用当前安装的<a href="c-error-set_constraint_handler_s.html">制约处理</a>函数：
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<dl>
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<dd>
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<ul>
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<li><code>ssz</code> 小于会被写入的字节数（除非 <code>s</code> 为空）</li>
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<li><code>ssz</code> 大于 <span class="t-lc">RSIZE_MAX</span> （除非 <code>s</code> 为空）</li>
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<li><code>s</code> 为空指针但 <code>ssz</code> 非零</li>
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</ul>
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</dd>
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<dd></dd>
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<dd>同所有边界检查函数， <code>wctomb_s</code> 仅若实现定义了 <span class="t-c"><span class="mw-geshi c source-c">__STDC_LIB_EXT1__</span></span> ，且用户在包含 <code><stdlib.h></code> 前定义 <span class="t-c"><span class="mw-geshi c source-c">__STDC_WANT_LIB_EXT1__</span></span> 为整数常量 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 才保证可用。</dd>
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</dl>
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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>每次对 <code>wctomb</code> 的调用更新全局转换状态（ <span class="t-lc"><a href="c-string-multibyte-mbstate_t.html">mbstate_t</a></span> 类型的静态对象，只为此函数所知）。若多字节编码使用迁移状态，则此函数不可重入。任何情况下，多个线程不应调用 <code>wctomb</code> 而不同步：可使用 <span class="t-lc"><a href="c-string-multibyte-wcrtomb.html">wcrtomb</a></span> 或 <code>wctomb_s</code> 代替。</p>
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<p>不同于大多数边界检查函数， <code>wctomb_s</code> 不以空字符终止其输出，因为它被设计以用于逐字节处理的循环。</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>s</td>
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<td>-</td>
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<td>指向输出用字符数组的指针</td>
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</tr>
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<tr class="t-par">
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<td>wc</td>
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<td>-</td>
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<td>要转换的宽字符</td>
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</tr>
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<tr class="t-par">
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<td>ssz</td>
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<td>-</td>
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<td>要写入 <code>s</code> 的最大字节数（数组 <code>s</code> 的大小）</td>
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</tr>
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<tr class="t-par">
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<td>status</td>
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<td>-</td>
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<td>指向结果（多字节序列长度或迁移序列状态）存储位置的输出参数的指针</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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<div class="t-li1"><span class="t-li">1)</span> 若 <code>s</code> 非空指针，则返回 <code>wc</code> 的多字节表示所含的字节数，或者若 <code>wc</code> 非合法字符则为 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">-</span><span class="nu0">1</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li"></span> 若 <code>s</code> 是空指针，则重设内部转换状态以表示初始迁移状态，并若当前多字节编码非状态依赖（不使用迁移序列）则返回 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> ，或者若当前多字节编码为状态依赖（使用迁移序列）则返回非零值。</div>
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<div class="t-li1"><span class="t-li">2)</span> 成功时为零，此情况下存储 <code>wc</code> 的多字节表示于 <code>s</code> ，并存储其长度于 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">*</span>status</span></span> ，或若 <code>s</code> 为空，则存储迁移序列状态于 <code>*status</code> 。编码错误或运行时制约错误发生时为非零，此情况下存储 <span class="t-c"><span class="mw-geshi c source-c"><span class="br0">(</span><a href="c-types-size_t.html"><span class="kw100">size_t</span></a><span class="br0">)</span><span class="sy2">-</span><span class="nu0">1</span></span></span> 于 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">*</span>status</span></span> 。存储于 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">*</span>status</span></span> 的值决不超过 <span class="t-lc">MB_CUR_MAX</span> 。</div>
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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="c source-c">
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<pre class="de1"><span class="co2">#include <stdio.h></span>
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<span class="co2">#include <stdlib.h></span>
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<span class="co2">#include <locale.h></span>
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<span class="kw4">void</span> demo<span class="br0">(</span><span class="kw4">wchar_t</span> wc<span class="br0">)</span>
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<span class="br0">{</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"State-dependent encoding? %d<span class="es1">\n</span>"</span>, wctomb<span class="br0">(</span><a href="c-types-NULL.html"><span class="kw103">NULL</span></a>, wc<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">char</span> mb<span class="br0">[</span>MB_CUR_MAX<span class="br0">]</span><span class="sy4">;</span>
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<span class="kw4">int</span> len <span class="sy1">=</span> wctomb<span class="br0">(</span>mb,wc<span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"wide char '%lc' -> multibyte char '"</span>, wc<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> idx <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> idx <span class="sy1"><</span> len<span class="sy4">;</span> <span class="sy2">++</span>idx<span class="br0">)</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%#2x "</span>, <span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="br0">)</span>mb<span class="br0">[</span>idx<span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"'<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</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="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="c-locale-setlocale.html"><span class="kw900">setlocale</span></a><span class="br0">(</span><a href="c-locale-LC_categories.html"><span class="kw903">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="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"MB_CUR_MAX = %zu<span class="es1">\n</span>"</span>, MB_CUR_MAX<span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span>L<span class="st0">'A'</span><span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span>L<span class="st0">'<span class="es3">\u00df</span>'</span><span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span>L<span class="st0">'<span class="es4">\U0001d10b</span>'</span><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>可能的输出：</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">MB_CUR_MAX = 6
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State-dependent encoding? 0
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wide char 'A' -> multibyte char '0x41 '
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State-dependent encoding? 0
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wide char 'ß' -> multibyte char '0xc3 0x9f '
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State-dependent encoding? 0
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wide char '𝄋' -> multibyte char '0xf0 0x9d 0x84 0x8b '</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准（ISO/IEC 9899:2011）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.22.7.3 The wctomb function (p: 358-359)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>K.3.6.4.1 The wctomb_s function (p: 610-611)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准（ISO/IEC 9899:1999）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.20.7.3 The wctomb function (p: 322-323)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c89">
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<ul>
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<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>4.10.7.3 The wctomb function</li>
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</ul>
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</dd>
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</dl>
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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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<td>
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<div class="t-dsc-member-div">
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<div><a href="c-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="c-string-multibyte-wcrtomb.html"><span class="t-lines"><span>wcrtomb</span><span>wcrtomb_s</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-c95">(C95)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div>
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</div>
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</td>
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<td>给定状态，将宽字符转换成其多字节表示<br />
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<span class="t-mark">(函数)</span></td>
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</table>
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</div>
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<div class="visualClear"></div>
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