204 lines
14 KiB
HTML
204 lines
14 KiB
HTML
<!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>mblen</title>
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_string_multibyte_mblen 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">mblen</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 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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<td>
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<div>定义于头文件 <code><stdlib.h></code></div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl">
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<div><span class="mw-geshi c source-c"><span class="kw4">int</span> mblen<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> s, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> n <span class="br0">)</span><span class="sy4">;</span></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>确定 <code>s</code> 指向其首字节的多字节字符的字节大小。</p>
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<p>若 <code>s</code> 是空指针，则<span class="t-rev-inl t-until-c23"><span>重置全局转换状态并</span> <span><span class="t-mark-rev t-until-c23">(C23 前)</span></span></span>确定是否使用迁移序列。</p>
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<p>此函数等价于调用 <span class="t-c"><span class="mw-geshi c source-c"><a href="c-string-multibyte-mbtowc.html"><span class="kw575">mbtowc</span></a><span class="br0">(</span><span class="br0">(</span><span class="kw4">wchar_t</span><span class="sy2">*</span><span class="br0">)</span><span class="nu0">0</span>, s, n<span class="br0">)</span></span></span> ，除了 <span class="t-lc"><a href="c-string-multibyte-mbtowc.html">mbtowc</a></span> 的转换状态不受影响。</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>指向多字节字符的指针</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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</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>若 <code>s</code> 不是空指针，则返回多字节字符所含的字节数，或若 <code>s</code> 所指的首字节不组成合法多字节字符则返回 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">-</span><span class="nu0">1</span></span></span> ，或若 <code>s</code> 指向空字符 <span class="t-c"><span class="mw-geshi c source-c"><span class="st0">'<span class="es5">\0</span>'</span></span></span> 则返回 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> 。</p>
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<p>若 <code>s</code> 是空指针，则<span class="t-rev-inl t-until-c23"><span>重置内部转换状态为初始迁移状态，</span> <span><span class="t-mark-rev t-until-c23">(C23 前)</span></span></span>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。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<table class="t-rev-begin">
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<tr class="t-rev t-until-c23">
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<td>
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<p>每次对 <code>mblen</code> 的调用更新内部全局转换状态（ <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，则必须留意以避免回撤或多次扫描。任何情况下，多线程不应无同步地调用 <code>mblen</code> ：可用 <span class="t-lc"><a href="c-string-multibyte-mbrlen.html">mbrlen</a></span> 代替。</p>
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</td>
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<td><span class="t-mark-rev t-until-c23">(C23 前)</span></td>
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</tr>
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<tr class="t-rev t-since-c23">
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<td>
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<p>不允许 <code>mblen</code> 拥有内部状态。</p>
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</td>
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<td><span class="t-mark-rev t-since-c23">(C23 起)</span></td>
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</tr>
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</table>
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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 <string.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="co2">#include <stdio.h></span>
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<span class="co1">// 多字节字符串的字符数是 mblen() 的和</span>
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<span class="co1">// 注意：更简单的手段是 mbstowcs(NULL, str, sz)</span>
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<a href="c-types-size_t.html"><span class="kw100">size_t</span></a> strlen_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="c-types-size_t.html"><span class="kw100">size_t</span></a> result <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</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="c-string-byte-strlen.html"><span class="kw558">strlen</span></a><span class="br0">(</span>ptr<span class="br0">)</span><span class="sy4">;</span>
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mblen<span class="br0">(</span><a href="c-types-NULL.html"><span class="kw103">NULL</span></a>, <span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 重置转换状态</span>
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<span class="kw1">while</span><span class="br0">(</span>ptr <span class="sy1"><</span> end<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">int</span> next <span class="sy1">=</span> mblen<span class="br0">(</span>ptr, end <span class="sy2">-</span> ptr<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>next <span class="sy1">==</span> <span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="c-io-perror.html"><span class="kw878">perror</span></a><span class="br0">(</span><span class="st0">"strlen_mb"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">break</span><span class="sy4">;</span>
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<span class="br0">}</span>
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ptr <span class="sy2">+</span><span class="sy1">=</span> next<span class="sy4">;</span>
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<span class="sy2">++</span>result<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">return</span> result<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> dump_bytes<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> str<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> end <span class="sy1">=</span> str <span class="sy2">+</span> <a href="c-string-byte-strlen.html"><span class="kw558">strlen</span></a><span class="br0">(</span>str<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> str <span class="sy3">!</span><span class="sy1">=</span> end<span class="sy4">;</span> <span class="sy2">++</span>str<span class="br0">)</span> <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">"%02X "</span>, <span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="br0">)</span>str<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span><span class="br0">)</span><span class="sy4">;</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">"<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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<span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> str <span class="sy1">=</span> <span class="st0">"z<span class="es3">\u00df</span><span class="es3">\u6c34</span><span class="es4">\U0001f34c</span>"</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">"The string <span class="es1">\"</span>%s<span class="es1">\"</span> consists of %zu characters, but %zu bytes: "</span>,
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str, strlen_mb<span class="br0">(</span>str<span class="br0">)</span>, <a href="c-string-byte-strlen.html"><span class="kw558">strlen</span></a><span class="br0">(</span>str<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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dump_bytes<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>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">The string "zß水🍌" consists of 4 characters, but 10 bytes: 7A C3 9F E6 B0 B4 F0 9F 8D 8C</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-17">
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<ul>
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<li>C17 标准（ISO/IEC 9899:2018）：</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>7.22.7.1 The mblen function (p: 260)</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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<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>7.22.7.1 The mblen function (p: 357)</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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<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>7.20.7.1 The mblen function (p: 321)</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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<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>4.10.7.1 The mblen 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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<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-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-mbrlen.html"><span class="t-lines"><span>mbrlen</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></div>
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</div>
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</td>
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<td>给定状态，返回下一个多字节字符的字节数<br />
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<span class="t-mark">(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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