175 lines
9.7 KiB
HTML
175 lines
9.7 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>strlen, strnlen_s</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_string_byte_strlen 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">strlen, strnlen_s</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-string.html">string</a>‎ | <a href="c-string-byte.html">byte</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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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><string.h></code></div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi c source-c"><a href="c-types-size_t.html"><span class="kw100">size_t</span></a> strlen<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>str <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl t-since-c11">
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<td>
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<div><span class="mw-geshi c source-c"><a href="c-types-size_t.html"><span class="kw100">size_t</span></a> strnlen_s<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>str, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> strsz <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<div class="t-li1"><span class="t-li">1)</span> 返回给定空终止字符串的长度，即首元素为 <code>str</code> 所指，且不包含首个空字符的字符数组中的字符数。</div>
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<div class="t-li1"><span class="t-li"></span> 若 <code>str</code> 不是指向空终止字节字符串的指针则行为未定义。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，除了若 <code>str</code> 为空指针则返回零，而若在 <code>str</code> 的首 <code>strsz</code> 个字节找不到空字符则返回 <code>strsz</code> 。</div>
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<div class="t-li1"><span class="t-li"></span> 若 <code>str</code> 指向缺少空字符的字符数组且该字符数组的大小 < <code>strsz</code> 则行为未定义；换言之， <code>strsz</code> 的错误值不会暴露行将来临的缓冲区溢出。
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<dl>
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<dd></dd>
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<dd>同所有边界检查函数， <code>strnlen_s</code> 仅若实现定义了 <span class="t-c"><span class="mw-geshi c source-c">__STDC_LIB_EXT1__</span></span> ，且用户在包含 <code><string.h></code> 前定义 <span class="t-c"><span class="mw-geshi c source-c">__STDC_WANT_LIB_EXT1__</span></span> 为整数常量 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 才保证可用。。</dd>
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</dl>
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</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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<tr class="t-par">
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<td>str</td>
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<td>-</td>
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<td>指向要检测的空终止字符串的指针</td>
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</tr>
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<tr class="t-par">
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<td>strsz</td>
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<td>-</td>
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<td>要检测的最大字符数量</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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<div class="t-li1"><span class="t-li">1)</span> 空终止字节字符串 <code>str</code> 的长度。</div>
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<div class="t-li1"><span class="t-li">2)</span> 成功时为空终止字节字符串 <code>str</code> 的长度，若 <code>str</code> 是空指针则为零，若找不到空字符则为 <code>strsz</code> 。</div>
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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><code>strnlen_s</code> 与 <code>wcsnlen_s</code> 是仅有的不调用运行时制约处理的<a href="c-error.html">边界检查函数</a>。它们是用于提供空终止字符串受限制支持的纯功能函数。</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="c source-c">
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<pre class="de1"><span class="co2">#define __STDC_WANT_LIB_EXT1__ 1</span>
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<span class="co2">#include <string.h></span>
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<span class="co2">#include <stdio.h></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">const</span> <span class="kw4">char</span> str<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"How many characters does this string contain?"</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"without null character: %zu<span class="es1">\n</span>"</span>, strlen<span class="br0">(</span>str<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"with null character: %zu<span class="es1">\n</span>"</span>, <span class="kw4">sizeof</span> str<span class="br0">)</span><span class="sy4">;</span>
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<span class="co2">#ifdef __STDC_LIB_EXT1__</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"without null character: %zu<span class="es1">\n</span>"</span>, strnlen_s<span class="br0">(</span>str, <span class="kw4">sizeof</span> str<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co2">#endif</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">without null character: 45
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with null character: 46
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without null character: 45</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准（ISO/IEC 9899:2011）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.24.6.3 The strlen function (p: 372)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>K.3.7.4.4 The strnlen_s function (p: 623)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准（ISO/IEC 9899:1999）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.21.6.3 The strlen function (p: 334)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c89">
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<ul>
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<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>4.11.6.3 The strlen function</li>
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</ul>
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</dd>
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</dl>
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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="c-string-wide-wcslen.html"><span class="t-lines"><span>wcslen</span><span>wcsnlen_s</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-c95">(C95)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div>
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</div>
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</td>
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<td>返回宽字符串的长度<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="c-string-multibyte-mblen.html"><span class="t-lines"><span>mblen</span></span></a></div>
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</div>
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</td>
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<td>返回下一个多字节字符的字节数<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>
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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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</div>
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</body>
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</html>
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