131 lines
8.8 KiB
HTML
131 lines
8.8 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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<title>std::wctob</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_wctob skin-cppreference2 action-view cpp-navbar">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>wctob</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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<table class="t-dcl-begin">
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<td>
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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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> wctob<span class="br0">(</span> std<span class="sy4">::</span><span class="me2">wint_t</span> c <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td></td>
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<td></td>
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</tbody>
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</table>
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<p>窄化宽字符 <code>c</code> ，若其多字节字符等价版本在初始迁移状态为单字节。</p>
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<p>这典型地对来自 ASCII 字符集的字符可行，因为大多数多字节编码（例如 UTF-8 ）用单字节编码那些字符。</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>c</td>
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<td>-</td>
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<td>要窄化的宽字符</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>c</code> 在初始迁移状态不表示长度为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span></span></span> 的多字节字符则为 <span class="t-lc"><a href="cpp-io-c.html">EOF</a></span> 。</p>
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<p>否则，为作为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> 的 <code>c</code> 的单字节表示，转换为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</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="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 <clocale></span>
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<span class="co2">#include <cwchar></span>
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<span class="co2">#include <iostream></span>
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<span class="kw4">void</span> try_narrowing<span class="br0">(</span><span class="kw4">wchar_t</span> c<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> cn <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">wctob</span><span class="br0">(</span>c<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>cn <span class="sy3">!</span><span class="sy1">=</span> <a href="cpp-io-c.html"><span class="kw1881">EOF</span></a><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">'<span class="es1">\'</span>'</span> <span class="sy1"><<</span> c <span class="sy1"><<</span> <span class="st0">"' narrowed to "</span> <span class="sy1"><<</span> <span class="sy2">+</span>cn <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">else</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">'<span class="es1">\'</span>'</span> <span class="sy1"><<</span> c <span class="sy1"><<</span> <span class="st0">"' could not be narrowed<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> 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">"th_TH.utf8"</span><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> <a href="cpp-io-manip-hex.html"><span class="kw1781">std::<span class="me2">hex</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-showbase.html"><span class="kw1765">std::<span class="me2">showbase</span></span></a> <span class="sy1"><<</span> <span class="st0">"In Thai UTF-8 locale:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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try_narrowing<span class="br0">(</span>L<span class="st0">'a'</span><span class="br0">)</span><span class="sy4">;</span>
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try_narrowing<span class="br0">(</span>L<span class="st0">'๛'</span><span class="br0">)</span><span class="sy4">;</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">"th_TH.tis620"</span><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">"In Thai TIS-620 locale:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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try_narrowing<span class="br0">(</span>L<span class="st0">'a'</span><span class="br0">)</span><span class="sy4">;</span>
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try_narrowing<span class="br0">(</span>L<span class="st0">'๛'</span><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">In Thai UTF-8 locale:
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'0x61' narrowed to 0x61
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'0xe5b' could not be narrowed
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In Thai TIS-620 locale:
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'0x61' narrowed to 0x61
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'0xe5b' narrowed to 0xfb</pre></div>
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</div>
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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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-btowc.html"><span class="t-lines"><span>btowc</span></span></a></div>
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</div>
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</td>
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<td>若可能，则加宽单字节窄字符为宽字符<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="cpp-io-basic_ios-narrow.html"><span class="t-lines"><span>narrow</span></span></a></div>
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</div>
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</td>
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<td>窄化字符<br />
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<span class="t-mark">(<code>std::basic_ios<CharT,Traits></code> 的公开成员函数)</span></td>
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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="cpp-locale-ctype-narrow.html"><span class="t-lines"><span>narrow</span></span></a></div>
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</div>
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</td>
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<td>调用 <code>do_narrow</code><br />
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<span class="t-mark">(<code>std::ctype<CharT></code> 的公开成员函数)</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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</body>
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