137 lines
11 KiB
HTML
137 lines
11 KiB
HTML
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<title>std::wctomb</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_wctomb 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>wctomb</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-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> 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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<p>转换宽字符 <code>wc</code> 为多字节编码并存储之（包含任何迁移序列）于首元素为 <code>s</code> 所指向的字符数组。不存储多于 <span class="t-c"><span class="mw-geshi cpp source-cpp">MB_CUR_MAX</span></span> 个字符。</p>
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<p>若 <code>wc</code> 是空字符，则将空字节写入 <code>s</code> ，前附任何需要恢复到初始迁移状态的迁移序列。</p>
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<p>若 <code>s</code> 是空指针，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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<tr class="t-par">
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<td>s</td>
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<td>-</td>
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<td>指向输出的字符数组的指针</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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</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 <code>wc</code> 的多字节表示中的字节数，或若 <code>wc</code> 不是合法字符则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> 。</p>
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<p>若 <code>s</code> 是空指针，则重置其内部转换状态为表示初始迁移状态，且若当前多字节编码不依赖状态（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以来状态（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>每次到 <code>wctomb</code> 的调用更新全局转换状态（ <span class="t-lc"><a href="cpp-string-multibyte-mbstate_t.html">std::mbstate_t</a></span> 类型静态对象，仅为此函数所知）。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：可用 <span class="t-lc"><a href="cpp-string-multibyte-wcrtomb.html">std::wcrtomb</a></span> 替代。</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 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="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 <cstdlib></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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<span class="kw4">bool</span> shifts <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">wctomb</span><span class="br0">(</span>nullptr, <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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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"shift sequences "</span> <span class="sy1"><<</span> <span class="br0">(</span>shifts <span class="sy4">?</span> <span class="st0">"are"</span> <span class="sy4">:</span> <span class="st0">"not"</span> <span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" used<span class="es1">\n</span>"</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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<span class="kw4">int</span> ret <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">wctomb</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="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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<span class="co1">// UTF-8 窄多字节编码</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">\U0001d10b</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">shift sequences not used
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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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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><a href="cpp-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 class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-wcrtomb.html"><span class="t-lines"><span>wcrtomb</span></span></a></div>
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<td>给定状态，转换宽字符到其多字节表示<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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