149 lines
13 KiB
HTML
149 lines
13 KiB
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<title>std::strxfrm</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_byte_strxfrm 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>strxfrm</h1>
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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-byte.html">byte</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-cstring.html"><cstring></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> strxfrm<span class="br0">(</span> <span class="kw4">char</span><span class="sy2">*</span> dest, <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> src, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> count <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>变换 <code>src</code> 所指向的空终止字节字符串为实现定义形式，满足当前 C 本地环境中，以 <span class="t-lc"><a href="cpp-string-byte-strcmp.html">std::strcmp</a></span> 比较二个变换后字符串给出与用 <span class="t-lc"><a href="cpp-string-byte-strcoll.html">std::strcoll</a></span> 比较源字符串相同的结果。</p>
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<p>将变换后字符串的首 <code>count</code> 个字符写入目标，包含空终止字符，并返回排除空终止字符的完整转换后字符串的长度。</p>
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<p>若 <code>dest</code> 数组不够大则行为未定义。若 <code>dest</code> 与 <code>src</code> 重叠则行为未定义。</p>
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<p>若 <code>count</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ，则允许 <code>dest</code> 为空指针。</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>能接收整个变换后字符串的正确缓冲区长度为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span><span class="sy2">+</span>std<span class="sy4">::</span><span class="me2">strxfrm</span><span class="br0">(</span><a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a>, src, <span class="nu0">0</span><span class="br0">)</span></span></span> 。</p>
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<p>在以同一字符串或字符串集合进行多个本地环境依赖的比较时，使用此函数，因为仅用 <code>std::strxfrm</code> 变换所有字符串一次，而以 <span class="t-lc"><a href="cpp-string-byte-strcmp.html">std::strcmp</a></span> 进行后继比较更为高效。</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>dest</td>
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<td>-</td>
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<td>指向将写入变换后的字符串的数组首元素的指针</td>
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<td>src</td>
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<td>-</td>
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<td>指向要变换的空终止字节字符串首元素的指针</td>
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</tr>
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<tr class="t-par">
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<td>count</td>
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<td>-</td>
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<td>要写入的最大字符数</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>变换后的字符串长度，不包含空终止字符。</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 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 <cstring></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <cassert></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">char</span><span class="sy2">*</span> loc <span class="sy1">=</span> <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="kw1993">LC_COLLATE</span></a>, <span class="st0">"cs_CZ.iso88592"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-error-assert.html"><span class="kw774">assert</span></a><span class="br0">(</span>loc<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a> in1 <span class="sy1">=</span> <span class="st0">"hrnec"</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a> out1<span class="br0">(</span><span class="nu0">1</span><span class="sy2">+</span>std<span class="sy4">::</span><span class="me2">strxfrm</span><span class="br0">(</span>nullptr, in1.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span>, <span class="nu0">0</span><span class="br0">)</span>, <span class="st0">' '</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a> in2 <span class="sy1">=</span> <span class="st0">"chrt"</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a> out2<span class="br0">(</span><span class="nu0">1</span><span class="sy2">+</span>std<span class="sy4">::</span><span class="me2">strxfrm</span><span class="br0">(</span>nullptr, in2.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span>, <span class="nu0">0</span><span class="br0">)</span>, <span class="st0">' '</span><span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">strxfrm</span><span class="br0">(</span><span class="sy3">&</span>out1<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, in1.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span>, out1.<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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std<span class="sy4">::</span><span class="me2">strxfrm</span><span class="br0">(</span><span class="sy3">&</span>out2<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, in2.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span>, out2.<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="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"In the Czech 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="kw1757">std::<span class="me2">cout</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="kw1757">std::<span class="me2">cout</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="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"In lexicographical 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="kw1757">std::<span class="me2">cout</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="kw1757">std::<span class="me2">cout</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 Czech locale: hrnec before chrt
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In lexicographical comparison: chrt before hrnec</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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<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>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 class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-locale-collate-transform.html"><span class="t-lines"><span>do_transform</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>变换字符串，使得能用比较替换对照<br />
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<span class="t-mark">(<code>std::collate<CharT></code> 的虚受保护成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-byte-strcoll.html"><span class="t-lines"><span>strcoll</span></span></a></div>
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<td>按照当前本地环境比较两个字符串<br />
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<span class="t-mark">(函数)</span></td>
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