138 lines
9.0 KiB
HTML
138 lines
9.0 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::tolower(std::locale)</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_locale_tolower 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>tolower<span style="font-size:0.7em; line-height:130%">(std::locale)</span></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-locale.html">locale</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-locale.html"><locale></a></code></div>
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<td></td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> charT <span class="sy1">></span><br />
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charT tolower<span class="br0">(</span> charT ch, <span class="kw4">const</span> locale<span class="sy3">&</span> loc <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>用给定 loacale 的 <span class="t-lc"><a href="cpp-locale-ctype.html">std::ctype</a></span> 平面所指定的转换规则，若可能则转换字符 <code>ch</code> 为小写。</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>ch</td>
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<td>-</td>
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<td>字符</td>
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</tr>
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<tr class="t-par">
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<td>loc</td>
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<td>-</td>
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<td>本地环境</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>ch</code> 的小写形式列于 locale 则返回它，否则返回不更改的 <code>ch</code> 。</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>此函数只能进行 1:1 字符映射。例如希腊文大写字母 'Σ' 拥有两个小写形式： 'σ' 与 'ς'，使用哪一个取决于其在词中的位置 。此情况下对 <code>do_tolower</code> 的调用不能获得正确的小写形式。</p>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> charT <span class="sy1">></span>
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charT tolower<span class="br0">(</span> charT ch, <span class="kw4">const</span> <a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="sy3">&</span> loc <span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> <a href="cpp-locale-use_facet.html"><span class="kw1897">std::<span class="me2">use_facet</span></span></a><span class="sy1"><</span><a href="cpp-locale-ctype.html"><span class="kw1938">std::<span class="me2">ctype</span></span></a><span class="sy1"><</span>charT<span class="sy1">>></span><span class="br0">(</span>loc<span class="br0">)</span>.<span class="me1">tolower</span><span class="br0">(</span>ch<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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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 <cwctype></span>
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<span class="co2">#include <locale></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="kw4">wchar_t</span> c <span class="sy1">=</span> L<span class="st0">'<span class="es3">\u0190</span>'</span><span class="sy4">;</span> <span class="co1">// 拉丁文大写开 E ('Ɛ')</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-hex.html"><span class="kw1782">std::<span class="me2">hex</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-showbase.html"><span class="kw1766">std::<span class="me2">showbase</span></span></a><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"in the default locale, tolower("</span> <span class="sy1"><<</span> <span class="br0">(</span>std<span class="sy4">::</span><span class="me2">wint_t</span><span class="br0">)</span>c <span class="sy1"><<</span> <span class="st0">") = "</span>
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<span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">tolower</span><span class="br0">(</span>c, <a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="br0">(</span><span class="br0">)</span><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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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"in Unicode locale, tolower("</span> <span class="sy1"><<</span> <span class="br0">(</span>std<span class="sy4">::</span><span class="me2">wint_t</span><span class="br0">)</span>c <span class="sy1"><<</span> <span class="st0">") = "</span>
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<span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">tolower</span><span class="br0">(</span>c, <a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="br0">(</span><span class="st0">"en_US.utf8"</span><span class="br0">)</span><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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</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 the default locale, tolower(0x190) = 0x190
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in Unicode locale, tolower(0x190) = 0x25b</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-locale-toupper.html"><span class="t-lines"><span>toupper<span class="t-dsc-small">(std::locale)</span></span></span></a></div>
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</div>
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</td>
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<td>用本地环境的 ctype 刻面将字符转换为大写<br />
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<span class="t-mark">(函数模板)</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-string-byte-tolower.html"><span class="t-lines"><span>tolower</span></span></a></div>
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</div>
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</td>
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<td>转换字符为小写<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-string-wide-towlower.html"><span class="t-lines"><span>towlower</span></span></a></div>
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</div>
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</td>
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<td>转换宽字符为小写<br />
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<span class="t-mark">(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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</body>
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