224 lines
15 KiB
HTML
224 lines
15 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>strcat, strcat_s</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_string_byte_strcat skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading">strcat, strcat_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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<td>
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<div>定义于头文件 <code><string.h></code></div>
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<td></td>
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<td></td>
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<tbody class="t-dcl-rev t-dcl-rev-num">
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<td></td>
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<td rowspan="142">(1)</td>
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<td></td>
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<tr class="t-dcl t-until-c99">
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<div><span class="mw-geshi c source-c"><span class="kw4">char</span> <span class="sy2">*</span>strcat<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 <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-until-c99">(C99 前)</span></td>
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<tr class="t-dcl t-since-c99">
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<div><span class="mw-geshi c source-c"><span class="kw4">char</span> <span class="sy2">*</span>strcat<span class="br0">(</span> <span class="kw4">char</span> <span class="sy2">*</span><span class="kw4">restrict</span> dest, <span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span><span class="kw4">restrict</span> src <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><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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</tbody>
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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">errno_t strcat_s<span class="br0">(</span><span class="kw4">char</span> <span class="sy2">*</span><span class="kw4">restrict</span> dest, rsize_t destsz, <span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span><span class="kw4">restrict</span> src<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> 后附 <code>src</code> 所指向的空终止字节字符串的副本到 <code>dest</code> 所指向的空终止字节字符串的结尾。字符 <code>src[0]</code> 替换 <code>dest</code> 末尾的空终止符。产生的字节字符串是空终止的。</div>
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<div class="t-li1"><span class="t-li"></span> 若目标数组对于 <code>src</code> 和 <code>dest</code> 的内容以及空终止符不够大，则行为未定义。若字符串重叠，则行为未定义。若 <code>dest</code> 或 <code>src</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> ，除了它可用未指定值破坏目标数组的剩余部分（从最后写入字符到 <code>destsz</code> ），以及在运行时检测下列错误，并调用当前安装的<a href="c-error-set_constraint_handler_s.html">制约处理</a>函数：
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<dl>
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<dd>
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<ul>
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<li><code>src</code> 或 <code>dest</code> 为空指针</li>
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<li><code>destsz</code> 为零或大于 <span class="t-lc">RSIZE_MAX</span></li>
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<li><code>dest</code> 的首 <code>destsz</code> 个字节中无空终止符</li>
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<li>会出现截断（ <code>dest</code> 末尾的可用空间不能适应 <code>src</code> 的每个字符，包括空终止符）</li>
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<li>源与目标字符串间会出现重叠</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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<div class="t-li1"><span class="t-li"></span> 若 <code>dest</code> 所指向的字符数组大小 < <span class="t-c"><span class="mw-geshi c source-c"><a href="c-string-byte-strlen.html"><span class="kw557">strlen</span></a><span class="br0">(</span>dest<span class="br0">)</span><span class="sy2">+</span><a href="c-string-byte-strlen.html"><span class="kw557">strlen</span></a><span class="br0">(</span>src<span class="br0">)</span><span class="sy2">+</span><span class="nu0">1</span></span></span> <= <code>destsz</code> 则行为未定义；换言之， <code>destsz</code> 的错误值不暴露行将发生的缓冲区溢出。
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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>strcat_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>dest</td>
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<td>-</td>
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<td>指向要后附到的空终止字节字符串的指针</td>
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</tr>
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<tr class="t-par">
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<td>src</td>
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<td>-</td>
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<td>指向作为复制来源的空终止字节字符串的指针</td>
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</tr>
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<tr class="t-par">
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<td>destsz</td>
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<td>-</td>
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<td>要写入的最大字符数，典型地为目标缓冲区的大小</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> 返回 <code>dest</code> 的副本。</div>
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<div class="t-li1"><span class="t-li">2)</span> 成功时返回零。错误时返回非零。错误时，亦写入零到 <span class="t-c"><span class="mw-geshi c source-c">dest<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span></span></span> （除非 <code>dest</code> 为空指针，或 <code>destsz</code> 为零或大于 <span class="t-lc">RSIZE_MAX</span> ）。</div>
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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>因为 <code>strcat</code> 需要在每次调用时找到 <code>dest</code> 的结尾，故用 <code>strcat</code> 将多个字符串连接成一体是低效的。</p>
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<p>为提升效率，允许 <code>strcat_s</code> 从最后被写入字符到 <code>destsz</code> 破坏目标数组：它可以用多字节块复制，然后检查空字节。</p>
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<p>函数 <code>strcat_s</code> 类似 BSD 函数 <code>strlcat</code> ，除了</p>
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<ul>
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<li><code>strlcat</code> 截断源字符串以适合目标</li>
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<li><code>strlcat</code> 不进行所有 <code>strcat_s</code> 进行的运行时检查</li>
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<li>若调用失败，则 <code>strlcat</code> 不设置目标为空字符串或调用处理函数，而令失败显著。</li>
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</ul>
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<p>尽管 <code>strcat_s</code> 由于潜在安全风险禁止截断，还可以用带边界检查的 <span class="t-lc"><a href="c-string-byte-strncat.html">strncat_s</a></span> 截断字符串。</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="co2">#include <stdlib.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">char</span> str<span class="br0">[</span><span class="nu0">50</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"Hello "</span><span class="sy4">;</span>
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<span class="kw4">char</span> str2<span class="br0">[</span><span class="nu0">50</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"World!"</span><span class="sy4">;</span>
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strcat<span class="br0">(</span>str, str2<span class="br0">)</span><span class="sy4">;</span>
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strcat<span class="br0">(</span>str, <span class="st0">" ..."</span><span class="br0">)</span><span class="sy4">;</span>
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strcat<span class="br0">(</span>str, <span class="st0">" Goodbye World!"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-puts.html"><span class="kw835">puts</span></a><span class="br0">(</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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set_constraint_handler_s<span class="br0">(</span>ignore_handler_s<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> r <span class="sy1">=</span> strcat_s<span class="br0">(</span>str, <span class="kw4">sizeof</span> str, <span class="st0">" ... "</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">"str = <span class="es1">\"</span>%s<span class="es1">\"</span>, r = %d<span class="es1">\n</span>"</span>, str, r<span class="br0">)</span><span class="sy4">;</span>
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r <span class="sy1">=</span> strcat_s<span class="br0">(</span>str, <span class="kw4">sizeof</span> str, <span class="st0">" and this is too much"</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">"str = <span class="es1">\"</span>%s<span class="es1">\"</span>, r = %d<span class="es1">\n</span>"</span>, str, r<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>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">Hello World! ... Goodbye World!
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str = "Hello World! ... Goodbye World! ... ", r = 0
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str = "", r = 22</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>7.24.3.1 The strcat function (p: 364)</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.3.7.2.1 The strcat_s function (p: 617-618)</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>7.21.3.1 The strcat function (p: 327)</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>4.11.3.1 The strcat 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-byte-strncat.html"><span class="t-lines"><span>strncat</span><span>strncat_s</span></span></a></div>
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<div><span class="t-lines"><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>连接两个字符串的一定数量字符<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="c-string-byte-strcpy.html"><span class="t-lines"><span>strcpy</span><span>strcpy_s</span></span></a></div>
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<div><span class="t-lines"><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>复制一个字符串给另一个<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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