144 lines
11 KiB
HTML
144 lines
11 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::wmemcmp</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_wide_wmemcmp skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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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>wmemcmp</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-wide.html">wide</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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<table class="t-dcl-begin">
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<td>
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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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> wmemcmp<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">wchar_t</span><span class="sy2">*</span> lhs, <span class="kw4">const</span> <span class="kw4">wchar_t</span><span class="sy2">*</span> rhs, <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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<td class="t-dcl-nopad"></td>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl-sep">
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<td></td>
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<p>比较 <code>lhs</code> 和 <code>rhs</code> 所指向的宽字符数组的首 <code>count</code> 个宽字符。按字典序比较。</p>
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<p>结果的符号是在被比较数组中相异的首对宽字符值的差。</p>
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<p>若 <code>count</code> 为零，则不做任何事。</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>lhs, rhs</td>
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<td>-</td>
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<td>指向要比较的宽字符数组的指针</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>要检验的宽字符数</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>若 <code>lhs</code> 中首个相异的宽字符小于 <code>rhs</code> 中对应的宽字符则为负值：字典序中 <code>lhs</code> 先于 <code>rhs</code> 。</p>
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<p>若 <code>lhs</code> 和 <code>rhs</code> 的全部 <code>count</code> 个宽字符相等则为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 。</p>
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<p>若 <code>lhs</code> 中首个相异的宽字符大于 <code>rhs</code> 中对应的宽字符则为正值：字典序中 <code>rhs</code> 先于 <code>lhs</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>此函数不考虑本地环境，且不注意其所检验的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">wchar_t</span></span></span> 对象的值：亦会比较空字符和非法宽字符。</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 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 <string></span>
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<span class="co2">#include <cwchar></span>
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<span class="co2">#include <locale></span>
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<span class="co2">#include <clocale></span>
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<span class="kw4">void</span> demo<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">wchar_t</span><span class="sy2">*</span> lhs, <span class="kw4">const</span> <span class="kw4">wchar_t</span><span class="sy2">*</span> rhs, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> sz<span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <a href="cpp-string-basic_string.html"><span class="kw1231">std::<span class="me2">wstring</span></span></a><span class="br0">(</span>lhs, sz<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> rc <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">wmemcmp</span><span class="br0">(</span>lhs, rhs, sz<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>rc <span class="sy1">==</span> <span class="nu0">0</span><span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <span class="st0">" compares equal to "</span><span class="sy4">;</span>
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<span class="kw1">else</span> <span class="kw1">if</span><span class="br0">(</span>rc <span class="sy1"><</span> <span class="nu0">0</span><span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <span class="st0">" precedes "</span><span class="sy4">;</span>
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<span class="kw1">else</span> <span class="kw1">if</span><span class="br0">(</span>rc <span class="sy1">></span> <span class="nu0">0</span><span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <span class="st0">" follows "</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <a href="cpp-string-basic_string.html"><span class="kw1231">std::<span class="me2">wstring</span></span></a><span class="br0">(</span>rhs, sz<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" in lexicographical order<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">"en_US.utf8"</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">wcout</span></span></a>.<span class="me1">imbue</span><span class="br0">(</span><a href="cpp-locale-locale.html"><span class="kw1893">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="sy4">;</span>
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<span class="kw4">wchar_t</span> a1<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span>L<span class="st0">'α'</span>,L<span class="st0">'β'</span>,L<span class="st0">'γ'</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> sz <span class="sy1">=</span> sizeof a1 <span class="sy2">/</span> sizeof <span class="sy2">*</span>a1<span class="sy4">;</span>
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<span class="kw4">wchar_t</span> a2<span class="br0">[</span>sz<span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span>L<span class="st0">'α'</span>,L<span class="st0">'β'</span>,L<span class="st0">'δ'</span><span class="br0">}</span><span class="sy4">;</span>
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demo<span class="br0">(</span>a1, a2, sz<span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span>a2, a1, sz<span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span>a1, a1, sz<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>可能的输出：</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">αβγ precedes αβδ in lexicographical order
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αβδ follows αβγ in lexicographical order
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αβγ compares equal to αβγ in lexicographical order</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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<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-wcscmp.html"><span class="t-lines"><span>wcscmp</span></span></a></div>
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</div>
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</td>
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<td>比较两个宽字符串<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-byte-memcmp.html"><span class="t-lines"><span>memcmp</span></span></a></div>
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</div>
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</td>
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<td>比较两个缓冲区<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-wcsncmp.html"><span class="t-lines"><span>wcsncmp</span></span></a></div>
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</div>
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</td>
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<td>比较来自两个宽字符串的一定量宽字符<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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</div>
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</body>
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