145 lines
10 KiB
HTML
145 lines
10 KiB
HTML
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<title>std::strncmp</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_byte_strncmp 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>strncmp</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-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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> strncmp<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> lhs, <span class="kw4">const</span> <span class="kw4">char</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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<p>比较二个可能空终止的数组的至多 <code>count</code> 个字符。按字典序进行比较。不比较后随空字符的字符。</p>
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<p>结果的符号是被比较的数组中首对字符（都转译成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> ）的值间的差的符号。</p>
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<p>若出现越过 <code>lhs</code> 或 <code>rhs</code> 结尾的访问，则行为未定义。若 <code>lhs</code> 或 <code>rhs</code> 为空指针，则行为未定义。</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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<td>lhs, rhs</td>
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<td>-</td>
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<td>指向要比较的可能空终止的数组的指针</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>要比较的最大字符数</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>若字典序中 <code>lhs</code> 先出现于 <code>rhs</code> 则为负值。</p>
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<p>若 <code>lhs</code> 与 <code>rhs</code> 比较相等，或若 count 为零，则为零。</p>
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<p>若字典序中 <code>lhs</code> 后出现于 <code>rhs</code> 则为正值。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>不同于 <span class="t-lc"><a href="cpp-string-byte-strcoll.html">std::strcoll</a></span> 和 <span class="t-lc"><a href="cpp-string-byte-strxfrm.html">std::strxfrm</a></span> ，此函数不考虑本地环境。</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 <cstring></span>
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<span class="co2">#include <iostream></span>
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<span class="kw4">void</span> demo<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> lhs, <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> rhs, <span class="kw4">int</span> sz<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> rc <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">strncmp</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="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"First "</span> <span class="sy1"><<</span> sz <span class="sy1"><<</span> <span class="st0">" chars of ["</span>
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<span class="sy1"><<</span> lhs <span class="sy1"><<</span> <span class="st0">"] equal ["</span> <span class="sy1"><<</span> rhs <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> <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="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"First "</span> <span class="sy1"><<</span> sz <span class="sy1"><<</span> <span class="st0">" chars of ["</span>
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<span class="sy1"><<</span> lhs <span class="sy1"><<</span> <span class="st0">"] precede ["</span> <span class="sy1"><<</span> rhs <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> <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="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"First "</span> <span class="sy1"><<</span> sz <span class="sy1"><<</span> <span class="st0">" chars of ["</span>
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<span class="sy1"><<</span> lhs <span class="sy1"><<</span> <span class="st0">"] follow ["</span> <span class="sy1"><<</span> rhs <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>
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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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demo<span class="br0">(</span><span class="st0">"Hello, world!"</span>, <span class="st0">"Hello, everybody!"</span>, <span class="nu0">13</span><span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span><span class="st0">"Hello, everybody!"</span>, <span class="st0">"Hello, world!"</span>, <span class="nu0">13</span><span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span><span class="st0">"Hello, everybody!"</span>, <span class="st0">"Hello, world!"</span>, <span class="nu0">7</span><span class="br0">)</span><span class="sy4">;</span>
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demo<span class="br0">(</span><span class="st0">"Hello, everybody!"</span> <span class="sy2">+</span> <span class="nu0">12</span>, <span class="st0">"Hello, somebody!"</span> <span class="sy2">+</span> <span class="nu0">11</span>, <span class="nu0">5</span><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>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">First 13 chars of [Hello, world!] follow [Hello, everybody!]
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First 13 chars of [Hello, everybody!] precede [Hello, world!]
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First 7 chars of [Hello, everybody!] equal [Hello, world!]
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First 5 chars of [body!] equal [body!]</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-byte-strcmp.html"><span class="t-lines"><span>strcmp</span></span></a></div>
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</div>
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</td>
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<td>比较两个字符串<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-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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<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-byte-strcoll.html"><span class="t-lines"><span>strcoll</span></span></a></div>
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</div>
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</td>
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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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</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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