141 lines
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141 lines
12 KiB
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<title>std::mbrlen</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_mbrlen 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>mbrlen</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-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> mbrlen<span class="br0">(</span> <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, <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>给定当前转换状态 <code>s</code> ，确定首字节为 <code>ps</code> 所指向的多字节字符的剩余字节大小。</p>
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<p>此函数等价于对于某 <span class="t-lc"><a href="cpp-string-multibyte-mbstate_t.html">std::mbstate_t</a></span> 类型的隐藏对象 <code>internal</code> 的调用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-string-multibyte-mbrtowc.html"><span class="kw1170">std::<span class="me2">mbrtowc</span></span></a><span class="br0">(</span>nullptr, s, n, ps<span class="sy4">?</span>ps<span class="sy4">:</span><span class="sy3">&</span>internal<span class="br0">)</span></span></span> ，除了只求值表达式 <code>ps</code> 一次。</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>指向多字节字符串元素的指针</td>
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<td>n</td>
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<td>-</td>
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<td>s 中能检验的字节数限制</td>
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<td>ps</td>
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<td>-</td>
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<td>指向保有转换状态的对象的指针</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>若下 <code>n</code> 个或更少字节完成空字符则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 。</p>
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<p>完成合法多字节字符的字节数（ <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">n</span></span> 之间）。</p>
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<p>若发生编码错误则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>size_t<span class="br0">)</span><span class="sy2">-</span><span class="nu0">1</span></span></span> 。</p>
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<p>若下 <code>n</code> 个字节为可能合法，而在检验全部 <code>n</code> 个字节后仍不完整的多字节字符的一部分，则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>size_t<span class="br0">)</span><span class="sy2">-</span><span class="nu0">2</span></span></span> 。</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <clocale></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <cwchar></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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<span class="co1">// 允许 mbrlen() 以 UTF-8 多字节编码工作</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="kw1229">std::<span class="me2">string</span></span></a> str <span class="sy1">=</span> u8<span class="st0">"水"</span><span class="sy4">;</span> <span class="co1">// 或 u8"\u6c34" 或 "\xe6\xb0\xb4"</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> mb <span class="sy1">=</span> <a href="cpp-string-multibyte-mbstate_t.html"><span class="kw1178">std::<span class="me2">mbstate_t</span></span></a><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> len1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">mbrlen</span><span class="br0">(</span><span class="sy3">&</span>str<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, <span class="nu0">1</span>, <span class="sy3">&</span>mb<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>len1 <span class="sy1">==</span> <span class="sy2">-</span><span class="nu0">2</span><span class="br0">)</span> <span class="br0">{</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">"The first 1 byte of "</span> <span class="sy1"><<</span> str
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<span class="sy1"><<</span> <span class="st0">" is an incomplete multibyte char (mbrlen returns -2)<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> len2 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">mbrlen</span><span class="br0">(</span><span class="sy3">&</span>str<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span>, str.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="nu0">1</span>, <span class="sy3">&</span>mb<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">"The remaining "</span> <span class="sy1"><<</span> str.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="nu0">1</span> <span class="sy1"><<</span> <span class="st0">" bytes of "</span> <span class="sy1"><<</span> str
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<span class="sy1"><<</span> <span class="st0">" hold "</span> <span class="sy1"><<</span> len2 <span class="sy1"><<</span> <span class="st0">" bytes of the multibyte character<span class="es1">\n</span>"</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">"Attempting to call mbrlen() in the middle of "</span> <span class="sy1"><<</span> str
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<span class="sy1"><<</span> <span class="st0">" while in initial shift state returns "</span>
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<span class="sy1"><<</span> <span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span>mbrlen<span class="br0">(</span><span class="sy3">&</span>str<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span>, str.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>, <span class="sy3">&</span>mb<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</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">The first 1 byte of 水 is an incomplete multibyte char (mbrlen returns -2)
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The remaining 2 bytes of 水 hold 2 bytes of the multibyte character
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Attempting to call mbrlen() in the middle of 水 while in initial shift state returns -1</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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<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>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-length.html"><span class="t-lines"><span>do_length</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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</td>
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<td>计算转换成给定的 internT 缓冲区会消耗的 externT 字符串长度<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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