136 lines
12 KiB
HTML
136 lines
12 KiB
HTML
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<title>std::collate<CharT>::transform, do_transform</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_locale_collate_transform 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::collate<CharT>::</span>transform, do_transform</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>‎ | <a href="cpp-locale-collate.html">collate</a></span></div>
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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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">public</span><span class="sy4">:</span><br />
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string_type transform<span class="br0">(</span> <span class="kw4">const</span> CharT<span class="sy2">*</span> low, <span class="kw4">const</span> CharT<span class="sy2">*</span> high <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">protected</span><span class="sy4">:</span><br />
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<span class="kw1">virtual</span> string_type do_transform<span class="br0">(</span> <span class="kw4">const</span> CharT<span class="sy2">*</span> low, <span class="kw4">const</span> CharT<span class="sy2">*</span> high <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<div class="t-li1"><span class="t-li">1)</span> 公开成员函数，调用最终导出类的受保护虚成员函数 <code>do_transform</code> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 转换字符序列 <code>[low, high)</code> 为 string ，使得它与在另一字符串上调用 <code>transform()</code> 的结果以字典序比较，会产生在二个相同字符串上调用 <span class="t-lc"><a href="cpp-locale-collate-compare.html">do_compare()</a></span> 的相同结果。</div>
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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>low</td>
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<td>-</td>
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<td>指向要变换的字符序列中首字符的指针</td>
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</tr>
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<tr class="t-par">
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<td>high</td>
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<td>-</td>
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<td>要变换的序列的尾后一位置指针</td>
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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>变换后的字符串，它使得被变换字符串的字典序比较能用于取代原字符串的对照。 "C" 本地环境中，返回的字符串为 <code>[low, high)</code> 的准确副本。其他本地环境中，返回字符串的内容是实现定义的，而且可考虑到大小可能更长。</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>在对照中的使用外，被变换字符串的本地环境限定格式还为 <a href="cpp-regex-regex_traits-transform_primary.html">std::regex_traits::transform_primary</a> 所知，它能释出等价类信息。</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 <iomanip></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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std<span class="sy4">::</span><span class="me2">locale</span><span class="sy4">::</span><span class="me2">global</span><span class="br0">(</span><a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="br0">(</span><span class="st0">"sv_SE.utf8"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">auto</span><span class="sy3">&</span> f <span class="sy1">=</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-collate.html"><span class="kw1943">std::<span class="me2">collate</span></span></a><span class="sy1"><</span><span class="kw4">wchar_t</span><span class="sy1">>></span><span class="br0">(</span><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="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1232">std::<span class="me2">wstring</span></span></a> in1 <span class="sy1">=</span> L<span class="st0">"<span class="es3">\u00e4</span>ngel"</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1232">std::<span class="me2">wstring</span></span></a> in2 <span class="sy1">=</span> L<span class="st0">"<span class="es3">\u00e5</span>r"</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1232">std::<span class="me2">wstring</span></span></a> out1 <span class="sy1">=</span> f.<span class="me1">transform</span><span class="br0">(</span><span class="sy3">&</span>in1<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, <span class="sy3">&</span>in1<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy2">+</span> in1.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1232">std::<span class="me2">wstring</span></span></a> out2 <span class="sy1">=</span> f.<span class="me1">transform</span><span class="br0">(</span><span class="sy3">&</span>in2<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, <span class="sy3">&</span>in2<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy2">+</span> in2.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1759">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <span class="st0">"In the Swedish locale: "</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>out1 <span class="sy1"><</span> out2<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1759">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> in1 <span class="sy1"><<</span> <span class="st0">" before "</span> <span class="sy1"><<</span> in2 <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="kw1759">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> in2 <span class="sy1"><<</span> <span class="st0">" before "</span> <span class="sy1"><<</span> in1 <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="kw1759">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <span class="st0">"In lexicographic comparison: "</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>in1 <span class="sy1"><</span> in2<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1759">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> in1 <span class="sy1"><<</span> <span class="st0">" before "</span> <span class="sy1"><<</span> in2 <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="kw1759">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> in2 <span class="sy1"><<</span> <span class="st0">" before "</span> <span class="sy1"><<</span> in1 <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 Swedish locale: år before ängel
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In lexicographic comparison: ängel before år</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-byte-strxfrm.html"><span class="t-lines"><span>strxfrm</span></span></a></div>
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</div>
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</td>
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<td>变换字符串，使得 strcmp 会返回与 strcoll 相同的结果<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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-wide-wcsxfrm.html"><span class="t-lines"><span>wcsxfrm</span></span></a></div>
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</div>
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</td>
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<td>变换宽字符串，使得 wcscmp 会产生与 wsccoll 相同的结果<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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