254 lines
19 KiB
HTML
254 lines
19 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>memcpy, memcpy_s</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_string_byte_memcpy skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading">memcpy, memcpy_s</h1>
|
|
<div id="bodyContent">
|
|
<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>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dsc-header">
|
|
<td>
|
|
<div>定义于头文件 <code><string.h></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody class="t-dcl-rev t-dcl-rev-num">
|
|
<tr class="t-dcl-rev-aux">
|
|
<td></td>
|
|
<td rowspan="142">(1)</td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl t-until-c99">
|
|
<td>
|
|
<div><span class="mw-geshi c source-c"><span class="kw4">void</span><span class="sy2">*</span> memcpy<span class="br0">(</span> <span class="kw4">void</span> <span class="sy2">*</span>dest, <span class="kw4">const</span> <span class="kw4">void</span> <span class="sy2">*</span>src, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> count <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-until-c99">(C99 前)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-c99">
|
|
<td>
|
|
<div><span class="mw-geshi c source-c"><span class="kw4">void</span><span class="sy2">*</span> memcpy<span class="br0">(</span> <span class="kw4">void</span> <span class="sy2">*</span><span class="kw4">restrict</span> dest, <span class="kw4">const</span> <span class="kw4">void</span> <span class="sy2">*</span><span class="kw4">restrict</span> src, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> count <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody>
|
|
<tr class="t-dcl t-since-c11">
|
|
<td>
|
|
<div><span class="mw-geshi c source-c">errno_t memcpy_s<span class="br0">(</span> <span class="kw4">void</span> <span class="sy2">*</span><span class="kw4">restrict</span> dest, rsize_t destsz,<br />
|
|
<span class="kw4">const</span> <span class="kw4">void</span> <span class="sy2">*</span><span class="kw4">restrict</span> src, rsize_t count <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(2)</td>
|
|
<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<div class="t-li1"><span class="t-li">1)</span> 从 <code>src</code> 所指向的对象复制 <code>count</code> 个字符到 <code>dest</code> 所指向的对象。两个对象都被转译成 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> 的数组。</div>
|
|
<div class="t-li1"><span class="t-li"></span> 若访问发生在 dest 数组结尾后则行为未定义。若对象重叠<span class="t-rev-inl t-since-c99"><span>（这违背 <a href="c-language-restrict.html"><tt>restrict</tt></a> 契约）</span> <span><span class="t-mark-rev t-since-c99">(C99 起)</span></span></span>，则行为未定义。若 <code>dest</code> 或 <code>src</code> 为非法或空指针则行为未定义。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，除了错误时导致清零整个目标范围 <span class="t-c"><span class="mw-geshi c source-c"><span class="br0">[</span>dest, dest<span class="sy2">+</span>destsz<span class="br0">)</span></span></span> （若 <code>dest</code> 与 <code>destsz</code> 均合法），它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：
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li><code>dest</code> 或 <code>src</code> 为空指针</li>
|
|
<li><code>destsz</code> 或 <code>count</code> 大于 <span class="t-lc">RSIZE_MAX</span></li>
|
|
<li><code>count</code> 大于 <code>destsz</code> （会发生缓冲区溢出）</li>
|
|
<li>源和目标对象重叠</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<div class="t-li1"><span class="t-li"></span> 若 <code>dest</code> 所指向的字符数组大小 < <code>count</code> <= <code>destsz</code> 则行为未定义；换言之，错误的 <code>destsz</code> 值不暴露行将发生的缓冲区溢出。
|
|
<dl>
|
|
<dd>同所有边界检查函数， <code>memcpy_s</code> 仅若实现定义 <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 1 才保证可用。</dd>
|
|
</dl>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>dest</td>
|
|
<td>-</td>
|
|
<td>指向要复制的对象的指针</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>destsz</td>
|
|
<td>-</td>
|
|
<td>目标中要修改的最大字节数（典型地为目标对象的大小）</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>src</td>
|
|
<td>-</td>
|
|
<td>指向复制来源对象的指针</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>count</td>
|
|
<td>-</td>
|
|
<td>复制的字节数</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<div class="t-li1"><span class="t-li">1)</span> 返回 <code>dest</code> 的副本，本质为更底层操作的临时内存地址，在实际操作中不建议直接使用此地址，操作完成以后，真正有意义的地址是 <code>dest</code> 本身。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 成功时返回零，错误时返回非零。在错误时，若 <code>dest</code> 不是空指针且 <code>destsz</code> 合法，则还会写入 <code>destsz</code> 个零字节到目标数组。</div>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p><code>memcpy</code> 可用于设置分配函数所获得对象的<a href="c-language-object.html#.E6.9C.89.E6.95.88.E7.B1.BB.E5.9E.8B">有效类型</a>。</p>
|
|
<p><code>memcpy</code> 是最快的内存到内存复制子程序。它通常比必须扫描其所复制数据的 <span class="t-lc"><a href="c-string-byte-strcpy.html">strcpy</a></span> ，或必须预防以处理重叠输入的 <span class="t-lc"><a href="c-string-byte-memmove.html">memmove</a></span> 更高效。</p>
|
|
<p>许多 C 编译器将适合的内存复制循环变换为 <code>memcpy</code> 调用。</p>
|
|
<p>在<a href="c-language-object.html#.E4.B8.A5.E6.A0.BC.E5.88.AB.E5.90.8D.E4.BD.BF.E7.94.A8">严格别名使用</a>禁止检验同一内存为二个不同类型的值处，可用 <code>memcpy</code> 转换值。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="co2">#define __STDC_WANT_LIB_EXT1__ 1</span>
|
|
<span class="co2">#include <stdio.h></span>
|
|
<span class="co2">#include <stdint.h></span>
|
|
<span class="co2">#include <inttypes.h></span>
|
|
<span class="co2">#include <string.h></span>
|
|
<span class="co2">#include <stdlib.h></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="co1">// 简单用法</span>
|
|
<span class="kw4">char</span> source<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"once upon a midnight dreary..."</span>, dest<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy4">;</span>
|
|
memcpy<span class="br0">(</span>dest, source, <span class="kw4">sizeof</span> dest<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">for</span><span class="br0">(</span><a href="c-types-size_t.html"><span class="kw100">size_t</span></a> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> n <span class="sy1"><</span> <span class="kw4">sizeof</span> dest<span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span>
|
|
<a href="c-io-putchar.html"><span class="kw834">putchar</span></a><span class="br0">(</span>dest<span class="br0">[</span>n<span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 设置分配的内存的有效类型为 int</span>
|
|
<span class="kw4">int</span> <span class="sy2">*</span>p <span class="sy1">=</span> <a href="c-memory-malloc.html"><span class="kw403">malloc</span></a><span class="br0">(</span><span class="nu0">3</span><span class="sy2">*</span><span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 分配的内存无有效类型</span>
|
|
<span class="kw4">int</span> arr<span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span><span class="br0">}</span><span class="sy4">;</span>
|
|
memcpy<span class="br0">(</span>p,arr,<span class="nu0">3</span><span class="sy2">*</span><span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 分配的内存现在拥有有效类型</span>
|
|
|
|
<span class="co1">// reinterpreting data</span>
|
|
<span class="kw4">double</span> d <span class="sy1">=</span> <span class="nu16">0.1</span><span class="sy4">;</span>
|
|
<span class="co1">// int64_t n = *(int64_t*)(&d); // 严格别名使用违规</span>
|
|
<a href="c-types-integer.html"><span class="kw109">int64_t</span></a> n<span class="sy4">;</span>
|
|
memcpy<span class="br0">(</span><span class="sy3">&</span>n, <span class="sy3">&</span>d, <span class="kw4">sizeof</span> d<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\n</span>%a is %"</span> <a href="c-types-integer.html"><span class="kw235">PRIx64</span></a> <span class="st0">" as an int64_t<span class="es1">\n</span>"</span>, d, n<span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co2">#ifdef __STDC_LIB_EXT1__</span>
|
|
set_constraint_handler_s<span class="br0">(</span>ignore_handler_s<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">char</span> src<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"aaaaaaaaaa"</span><span class="sy4">;</span>
|
|
<span class="kw4">char</span> dst<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"xyxyxyxyxy"</span><span class="sy4">;</span>
|
|
<span class="kw4">int</span> r <span class="sy1">=</span> memcpy_s<span class="br0">(</span>dst,<span class="kw4">sizeof</span> dst,src,<span class="nu0">5</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"dst = <span class="es1">\"</span>%s<span class="es1">\"</span>, r = %d<span class="es1">\n</span>"</span>, dst,r<span class="br0">)</span><span class="sy4">;</span>
|
|
r <span class="sy1">=</span> memcpy_s<span class="br0">(</span>dst,<span class="nu0">5</span>,src,<span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// count 大于 destsz </span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"dst = <span class="es1">\"</span>"</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">for</span><span class="br0">(</span><a href="c-types-size_t.html"><span class="kw100">size_t</span></a> ndx<span class="sy1">=</span><span class="nu0">0</span><span class="sy4">;</span> ndx<span class="sy1"><</span><span class="kw4">sizeof</span> dst<span class="sy4">;</span> <span class="sy2">++</span>ndx<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw4">char</span> c <span class="sy1">=</span> dst<span class="br0">[</span>ndx<span class="br0">]</span><span class="sy4">;</span>
|
|
c <span class="sy4">?</span> <a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%c"</span>, c<span class="br0">)</span> <span class="sy4">:</span> <a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\\</span>0"</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\"</span>, r = %d<span class="es1">\n</span>"</span>, r<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="co2">#endif</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>可能的输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">once
|
|
0x1.999999999999ap-4 is 3fb999999999999a as an int64_t
|
|
dst = "aaaaayxyxy", r = 0
|
|
dst = "\0\0\0\0\0yxyxy", r = 22</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
|
|
<div class="t-ref-std-11">
|
|
<ul>
|
|
<li>C11 标准（ISO/IEC 9899:2011）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>7.24.2.1 The memcpy function (p: 362)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>K.3.7.1.1 The memcpy_s function (p: 614)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<div class="t-ref-std-c99">
|
|
<ul>
|
|
<li>C99 标准（ISO/IEC 9899:1999）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>7.21.2.1 The memcpy function (p: 325)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<div class="t-ref-std-c89">
|
|
<ul>
|
|
<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>4.11.2.1 The memcpy function</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="c-string-byte-memccpy.html"><span class="t-lines"><span>memccpy</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c23">(C23)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>复制一个缓冲区到另一个，在指定的分隔符后停止<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="c-string-byte-memmove.html"><span class="t-lines"><span>memmove</span><span>memmove_s</span></span></a></div>
|
|
<div><span class="t-lines"><span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>将一个缓冲区移动到另一个<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="c-string-wide-wmemcpy.html"><span class="t-lines"><span>wmemcpy</span><span>wmemcpy_s</span></span></a></div>
|
|
<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>
|
|
</div>
|
|
</td>
|
|
<td>在两个不重叠的数组间复制一定数量的宽字符<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|