139 lines
11 KiB
HTML
139 lines
11 KiB
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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<title>std::mbtowc</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_mbtowc 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>mbtowc</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-cstdlib.html"><cstdlib></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> mbtowc<span class="br0">(</span> <span class="kw4">wchar_t</span><span class="sy2">*</span> pwc, <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> s, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>将 <code>s</code> 指向其首字节的多字节字符转换成宽字符，若 <code>pwc</code> 非空则写入 <code>*pwc</code> 。</p>
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<p>若 <code>s</code> 为空指针，则重置全局转换状态并确定是否使用迁移序列。</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>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的限制</td>
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</tr>
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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>指向输出用宽字符的指针</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>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 cpp source-cpp"><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 cpp source-cpp"><span class="st0">'<span class="es5">\0</span>'</span></span></span> 则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 。</p>
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<p>若 <code>s</code> 是空指针，则重置内部转换状态为初始迁移状态，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 cpp source-cpp">​<span class="nu0">0</span>​</span></span> ，或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。</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>每次对 <code>mbtowc</code> 的调用更新内部全局转换状态（ <span class="t-lc"><a href="cpp-string-multibyte-mbstate_t.html">std::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，多线程不应调用 <code>mbtowc</code> 而不同步：可用 <span class="t-lc"><a href="cpp-string-multibyte-mbrtowc.html">std::mbrtowc</a></span> 代替。</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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<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 <clocale></span>
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<span class="co2">#include <cstring></span>
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<span class="co2">#include <cstdlib></span>
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<span class="kw4">int</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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std<span class="sy4">::</span><span class="me2">mbtowc</span><span class="br0">(</span><a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a>, <span class="nu0">0</span>, <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="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> ret<span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">wchar_t</span> wc<span class="sy4">;</span> <span class="br0">(</span>ret <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">mbtowc</span><span class="br0">(</span><span class="sy3">&</span>wc, ptr, end<span class="sy2">-</span>ptr<span class="br0">)</span><span class="br0">)</span> <span class="sy1">></span> <span class="nu0">0</span><span class="sy4">;</span> ptr<span class="sy2">+</span><span class="sy1">=</span>ret<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> wc<span class="sy4">;</span>
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<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">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">return</span> ret<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="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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<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">zß水🍌</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-mbrtowc.html"><span class="t-lines"><span>mbrtowc</span></span></a></div>
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</div>
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</td>
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<td>给定状态，转换下个多字节字符为宽字符<br />
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<span class="t-mark">(函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-mblen.html"><span class="t-lines"><span>mblen</span></span></a></div>
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</td>
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<td>返回下一个多字节字符中的字节数<br />
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<span class="t-mark">(函数)</span></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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