91 lines
11 KiB
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91 lines
11 KiB
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<title>std::regex_traits<CharT>::transform_primary</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_regex_regex_traits_transform_primary 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::regex_traits<CharT>::</span>transform_primary</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-regex.html">regex</a>‎ | <a href="cpp-regex-regex_traits.html">regex traits</a></span></div>
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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> ForwardIt <span class="sy1">></span><br />
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string_type transform_primary<span class="br0">(</span> ForwardIt first, ForwardIt last <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<p>获得字符序列 <code>[first, last)</code> 在感染的本地环境的对照顺序中的初等排序关键，即基于国家字母表中，忽略大小写、发音符号、变体等的字母位置和对照单元的排序关键。若初等排序关键以 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1"><</span></span></span> 比较小于另一排序关键，则产生第一个排序关键的字符序列，在当前感染的本地环境的初等对照序列中，比生成第二个排序关键的字符序列先到来。</p>
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<p>正则表达式库用此特性将字符匹配到等价类。例如，正则表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="br0">[</span><span class="sy1">=</span>a<span class="sy1">=</span><span class="br0">]</span><span class="br0">]</span></span></span> 等价于字符 <code>c1</code> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">traits.<span class="me1">transform_primary</span><span class="br0">(</span>c1<span class="br0">)</span></span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">traits.<span class="me1">transform_primary</span><span class="br0">(</span><span class="st0">"a"</span><span class="br0">)</span></span></span> （这在美国英语本地环境中对来自 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">"AÀÁÂÃÄÅaàáâãäå"</span></span></span> 的任何 <code>c1</code> 为真）。注意 <code>transform_primary()</code> 接收字符序列参数，因为等价类可能是多字符，如捷克语中的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="br0">[</span><span class="sy1">=</span>ch<span class="sy1">=</span><span class="br0">]</span><span class="br0">]</span></span></span> 或匈牙利语中的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="br0">[</span><span class="sy1">=</span>dzs<span class="sy1">=</span><span class="br0">]</span><span class="br0">]</span></span></span> 。</p>
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<p>没有以 <span class="t-lc"><a href="cpp-locale-locale.html">std::locale</a></span> 定义初等排序关键的可移植方式，因为从 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">collate</span><span class="sy4">::</span><span class="me2">transform</span><span class="br0">(</span><span class="br0">)</span></span></span> 所返回的对照关键到初等等价关键的转换是本地环境限定的，而且若用户替换 <span class="t-lc"><a href="cpp-locale-collate.html">std::collate</a></span> 平面，则转换就不再是标准库的 <span class="t-lc"><a href="cpp-regex-regex_traits.html">std::regex_traits</a></span> 。 <span class="t-lc"><a href="cpp-regex-regex_traits.html">std::regex_traits</a></span> 的标准库特化返回空字符串，除非当前感染的本 locale 的 <span class="t-lc"><a href="cpp-locale-collate.html">std::collate</a></span> 平面未为用户所替换，并仍然匹配系统提供的 <span class="t-lc"><a href="cpp-locale-collate.html">std::collate</a></span> 平面，该情况下执行 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-locale-collate_byname.html"><span class="kw1978">std::<span class="me2">collate_byname</span></span></a><span class="sy1"><</span>charT<span class="sy1">></span><span class="sy4">::</span><span class="me2">transform</span><span class="br0">(</span>first, last<span class="br0">)</span></span></span> ，并用本地环境限定转换，转换其所产生的排序关键为初等排序关键。</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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<td>first, last</td>
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<td>-</td>
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<td>一对迭代器，确定要比较的字符序列</td>
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<td colspan="3">类型要求</td>
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<td colspan="3">-
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<code>ForwardIt</code> 必须满足<a href="cpp-named_req-ForwardIterator.html"><span style="font-style:italic">老式向前迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyForwardIterator)</span></a> 的要求。</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>当前感染的本地环境中字符序列 <code>[first, last)</code> 的初等排序关键，忽略大小写、变体、发音符号等。</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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<p>演示通过 transform_primary() 工作的正则表达式特性</p>
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<div class="t-example-live-link"></div>
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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 <regex></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">"en_US.UTF-8"</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> str <span class="sy1">=</span> L<span class="st0">"AÀÁÂÃÄÅaàáâãäå"</span><span class="sy4">;</span>
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<a href="cpp-regex-basic_regex.html"><span class="kw2001">std::<span class="me2">wregex</span></span></a> re<span class="br0">(</span>L<span class="st0">"[[=a=]]*"</span>, std<span class="sy4">::</span><span class="me2">regex</span><span class="sy4">::</span><span class="me2">basic</span><span class="br0">)</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> <a href="cpp-io-manip-boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a> <span class="sy1"><<</span> <a href="cpp-regex-regex_match.html"><span class="kw2012">std::<span class="me2">regex_match</span></span></a><span class="br0">(</span>str, re<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 class="text source-text">
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<pre class="de1">true</pre></div>
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<td class="mbox-text" style="">本节未完成<br />
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原因：可使用带提供用户定义 transform_primary 的用户定义 regex_traits 的示例</td>
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