131 lines
7.7 KiB
HTML
131 lines
7.7 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>strndup</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_experimental_dynamic_strndup 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">strndup</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-experimental.html">experimental</a>‎ | <a href="c-experimental-dynamic.html">dynamic</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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<div><span class="mw-geshi c source-c"><span class="kw4">char</span> <span class="sy2">*</span>strndup<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> size <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl-sep">
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<p>返回指向空终止字符串的指针，该字符串含有 <code>str</code> 所指向字符串的至多 <code>size</code> 字节的副本。若在其首 <code>size</code> 字节中遇到空终止符，则将它添加到复制的字符串中。</p>
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<p>必须传递返回指针给 <span class="t-lc"><a href="c-memory-free.html">free</a></span> ，以避免内存泄漏。</p>
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<p>若发生错误，则返回空指针，并可能设置 <span class="t-lc"><a href="c-error-errno.html">errno</a></span> 。</p>
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<p>同所有来自动态内存 TR 的函数， <code>strndup</code> 仅若实现定义了 <span class="t-c"><span class="mw-geshi c source-c">__STDC_ALLOC_LIB__</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_EXT2__</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。</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>str</td>
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<td>-</td>
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<td>指向要复制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>size</td>
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<td>-</td>
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<td>从 <code>str</code> 复制的最大字节数</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>指向新分配字符串的指针，若错误发生则为空指针。</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>此函数等同于 <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/strdup.html">POSIX strndup</a> ，除了允许但不要求它在错误时设置 <span class="t-lc"><a href="c-error-errno.html">errno</a></span> 。</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">#ifdef __STDC_ALLOC_LIB__</span>
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<span class="co2">#define __STDC_WANT_LIB_EXT2__ 1</span>
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<span class="co2">#else</span>
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<span class="co2">#define _POSIX_C_SOURCE 200809L</span>
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<span class="co2">#endif</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">const</span> <span class="kw4">char</span> <span class="sy2">*</span>s1 <span class="sy1">=</span> <span class="st0">"String"</span><span class="sy4">;</span>
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<span class="kw4">char</span> <span class="sy2">*</span>s2 <span class="sy1">=</span> strndup<span class="br0">(</span>s1, <span class="nu0">2</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"strndup(<span class="es1">\"</span>String<span class="es1">\"</span>, 2) == %s<span class="es1">\n</span>"</span>, s2<span class="br0">)</span><span class="sy4">;</span>
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<a href="c-memory-free.html"><span class="kw406">free</span></a><span class="br0">(</span>s2<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">strndup("String", 2) == St</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="c-experimental-dynamic-strdup.html"><span class="t-lines"><span>strdup</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-dynamic-tr t-mark-ts">(动态内存 TR)</span></span></span></div>
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</div>
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</td>
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<td>分配字符串的副本<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-strncpy.html"><span class="t-lines"><span>strncpy</span><span>strncpy_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>从一个字符串复制一定数量的字符到另一个<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<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-memory-malloc.html"><span class="t-lines"><span>malloc</span></span></a></div>
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</div>
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</td>
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<td>分配内存<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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<table class="t-dcl-begin">
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<tbody></tbody>
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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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</div>
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</body>
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</html>
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