129 lines
9.6 KiB
HTML
129 lines
9.6 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::btowc</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_btowc 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>btowc</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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<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">std<span class="sy4">::</span><span class="me2">wint_t</span> btowc<span class="br0">(</span> <span class="kw4">int</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>加宽单字节字符 <code>c</code> 为其宽字符等价物。</p>
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<p>大多数多字节字符编码用单字节码表示来自 ASCII 字符集的字符。此函数可用于转换这种字符为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">wchar_t</span></span></span> 。</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>要加宽的单字节字符</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> 为 <span class="t-lc"><a href="cpp-io-c.html">EOF</a></span> 则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">WEOF</span></span> 。</p>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="br0">)</span>c</span></span> 在初始迁移状态为合法单字节字符，则为 <code>c</code> 的宽字符表示，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">WEOF</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 <iostream></span>
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<span class="co2">#include <cwchar></span>
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<span class="co2">#include <clocale></span>
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<span class="kw4">void</span> try_widen<span class="br0">(</span><span class="kw4">char</span> c<span class="br0">)</span>
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<span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">wint_t</span> w <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">btowc</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>w <span class="sy3">!</span><span class="sy1">=</span> WEOF<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 single-byte character "</span> <span class="sy1"><<</span> <span class="sy2">+</span><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="br0">)</span>c
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<span class="sy1"><<</span> <span class="st0">" widens to "</span> <span class="sy1"><<</span> <span class="sy2">+</span>w <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">"The single-byte character "</span> <span class="sy1"><<</span> <span class="sy2">+</span><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="br0">)</span>c
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<span class="sy1"><<</span> <span class="st0">" failed to widen<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">"lt_LT.iso88594"</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 Lithuanian ISO-8859-4 locale:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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try_widen<span class="br0">(</span><span class="st0">'A'</span><span class="br0">)</span><span class="sy4">;</span>
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try_widen<span class="br0">(</span><span class="st0">'<span class="es2">\xdf</span>'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// ISO-8859-4 中的德文字母 ß (U+00df)</span>
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try_widen<span class="br0">(</span><span class="st0">'<span class="es2">\xf9</span>'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// ISO-8859-4 中的立陶宛字母 ų (U+0173)</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">"lt_LT.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> <span class="st0">"In Lithuanian UTF-8 locale:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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try_widen<span class="br0">(</span><span class="st0">'A'</span><span class="br0">)</span><span class="sy4">;</span>
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try_widen<span class="br0">(</span><span class="st0">'<span class="es2">\xdf</span>'</span><span class="br0">)</span><span class="sy4">;</span>
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try_widen<span class="br0">(</span><span class="st0">'<span class="es2">\xf9</span>'</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 Lithuanian ISO-8859-4 locale:
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The single-byte character 0x41 widens to 0x41
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The single-byte character 0xdf widens to 0xdf
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The single-byte character 0xf9 widens to 0x173
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In Lithuanian UTF-8 locale:
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The single-byte character 0x41 widens to 0x41
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The single-byte character 0xdf failed to widen
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The single-byte character 0xf9 failed to widen</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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<div class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-wctob.html"><span class="t-lines"><span>wctob</span></span></a></div>
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</div>
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</td>
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<td>若可能，则窄化宽字符为单字节窄字符<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-locale-ctype-widen.html"><span class="t-lines"><span>do_widen</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>将一或多个字符从 <code>char</code> 转换为 <code>charT</code><br />
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<span class="t-mark">(<code>std::ctype<CharT></code> 的虚受保护成员函数)</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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</div>
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</body>
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