138 lines
11 KiB
HTML
138 lines
11 KiB
HTML
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<title>std::wcrtomb</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_wcrtomb 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>wcrtomb</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-cwchar.html"><cwchar></a></code></div>
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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> wcrtomb<span class="br0">(</span> <span class="kw4">char</span><span class="sy2">*</span> s, <span class="kw4">wchar_t</span> wc, <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></span></div>
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<p>转换宽字符为其窄多字节表示。</p>
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<p>若 <code>s</code> 不是空指针，则函数检测存储 <code>wc</code> 的多字节字符表示所需的字节数（包含任何迁移序列，并考虑当前多字节转换状态 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> ，并存储多字节字符表示于首元素为 <code>s</code> 所指向的字符数组，按需更新 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 。此函数至多能写入 <span class="t-c"><span class="mw-geshi cpp source-cpp">MB_CUR_MAX</span></span> 字节。</p>
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<p>若 <code>s</code> 为空指针，则调用等价于对某内部缓冲区 <code>buf</code> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">wcrtomb<span class="br0">(</span>buf, L<span class="st0">'<span class="es5">\0</span>'</span>, ps<span class="br0">)</span></span></span> 。</p>
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<p>若 wc 是空宽字符 <span class="t-c"><span class="mw-geshi cpp source-cpp">L<span class="st0">'<span class="es5">\0</span>'</span></span></span> ，则存储空字节，前接任何恢复到初始迁移状态所需的迁移序列，并更新转换状态参数 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 以表示初始迁移状态。</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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<td>s</td>
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<td>-</td>
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<td>指向窄字符数组的指针，其中将存储多字节字符串</td>
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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 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>成功时，返回写入首元素为 <code>s</code> 所指向的字符数组的字节数（包含任何迁移序列）。</p>
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<p>失败时（若 <span class="t-c"><span class="mw-geshi cpp source-cpp">wc</span></span> 不是合法宽字符），返回 <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> ，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> ，并使 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 留在未指定状态。</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 <string></span>
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<span class="co2">#include <cwchar></span>
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<span class="kw4">void</span> print_wide<span class="br0">(</span><span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1231">std::<span class="me2">wstring</span></span></a><span class="sy3">&</span> wstr<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="br0">{</span><span class="br0">}</span><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> wstr<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a> mb<span class="br0">(</span>MB_CUR_MAX, <span class="st0">'<span class="es5">\0</span>'</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> ret <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">wcrtomb</span><span class="br0">(</span><span class="sy3">&</span>mb<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, wc, <span class="sy3">&</span>state<span class="br0">)</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">"multibyte char "</span> <span class="sy1"><<</span> mb <span class="sy1"><<</span> <span class="st0">" is "</span> <span class="sy1"><<</span> ret <span class="sy1"><<</span> <span class="st0">" bytes<span class="es1">\n</span>"</span><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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<a href="cpp-string-basic_string.html"><span class="kw1231">std::<span class="me2">wstring</span></span></a> wstr <span class="sy1">=</span> L<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 L"zß水🍌"</span>
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print_wide<span class="br0">(</span>wstr<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">multibyte char z is 1 bytes
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multibyte char ß is 2 bytes
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multibyte char 水 is 3 bytes
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multibyte char 🍌 is 4 bytes</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-wctomb.html"><span class="t-lines"><span>wctomb</span></span></a></div>
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</div>
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<td>转换宽字符为其多字节表示<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-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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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-locale-codecvt-out.html"><span class="t-lines"><span>do_out</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 internT 转换字符串为 externT 转换字符串，如在写入文件时<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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