143 lines
9.4 KiB
HTML
143 lines
9.4 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>malloc</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_memory_malloc skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading">malloc</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-memory.html">memory</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><stdlib.h></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td class="t-dcl-nopad">
|
|
<div><span class="mw-geshi c source-c"><span class="kw4">void</span><span class="sy2">*</span> malloc<span class="br0">(</span> <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>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>分配 <code>size</code> 字节的未初始化内存。</p>
|
|
<p>若分配成功，则返回为任何拥有<a href="c-language-object.html#.E5.AF.B9.E9.BD.90">基础对齐</a>的对象类型对齐的指针。</p>
|
|
<p>若 <code>size</code> 为零，则 <code>malloc</code> 的行为是实现定义的。例如可返回空指针。亦可返回非空指针；但不应当<a href="c-language-operator_member_access.html">解引用</a>这种指针，而且应将它传递给 <span class="t-lc"><a href="c-memory-free.html">free</a></span> 以避免内存泄漏。</p>
|
|
<table class="t-rev-begin">
|
|
<tr class="t-rev t-since-c11">
|
|
<td>
|
|
<p><code>malloc</code> 是线程安全的：它表现得如同只访问通过其参数可见的内存区域，而非任何静态存储。</p>
|
|
<p>令 <span class="t-lc"><a href="c-memory-free.html">free</a></span> 或 <span class="t-lc"><a href="c-memory-realloc.html">realloc</a></span> 归还一块内存区域的先前调用，<i>同步于</i>令 <code>malloc</code> 分配相同或部分相同的内存区域的调用。此同步出现于任何通过解分配函数所作的内存访问后，和任何 <code>malloc</code> 所作的内存访问前。所有操作每块特定内存区域的分配和解分配函数有单独全序。</p>
|
|
</td>
|
|
<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
|
|
</tr>
|
|
</table>
|
|
<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>size</td>
|
|
<td>-</td>
|
|
<td>要分配的字节数</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p>成功时，返回指向新分配内存的指针。为避免内存泄漏，必须用 <span class="t-lc"><a href="c-memory-free.html">free()</a></span> 或 <span class="t-lc"><a href="c-memory-realloc.html">realloc()</a></span> 解分配返回的指针。</p>
|
|
<p>失败时，返回空指针。</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">#include <stdio.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="kw4">int</span> <span class="sy2">*</span>p1 <span class="sy1">=</span> malloc<span class="br0">(</span><span class="nu0">4</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">// 足以分配 4 个 int 的数组</span>
|
|
<span class="kw4">int</span> <span class="sy2">*</span>p2 <span class="sy1">=</span> malloc<span class="br0">(</span><span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 等价，直接命名数组类型</span>
|
|
<span class="kw4">int</span> <span class="sy2">*</span>p3 <span class="sy1">=</span> malloc<span class="br0">(</span><span class="nu0">4</span><span class="sy2">*</span><span class="kw4">sizeof</span> <span class="sy2">*</span>p3<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 等价，免去重复类型名</span>
|
|
|
|
<span class="kw1">if</span><span class="br0">(</span>p1<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> n<span class="sy1">=</span><span class="nu0">0</span><span class="sy4">;</span> n<span class="sy1"><</span><span class="nu0">4</span><span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span> <span class="co1">// 置入数组</span>
|
|
p1<span class="br0">[</span>n<span class="br0">]</span> <span class="sy1">=</span> n<span class="sy2">*</span>n<span class="sy4">;</span>
|
|
<span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> n<span class="sy1">=</span><span class="nu0">0</span><span class="sy4">;</span> n<span class="sy1"><</span><span class="nu0">4</span><span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span> <span class="co1">// 打印出来</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"p1[%d] == %d<span class="es1">\n</span>"</span>, n, p1<span class="br0">[</span>n<span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<a href="c-memory-free.html"><span class="kw405">free</span></a><span class="br0">(</span>p1<span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-memory-free.html"><span class="kw405">free</span></a><span class="br0">(</span>p2<span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-memory-free.html"><span class="kw405">free</span></a><span class="br0">(</span>p3<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">p1[0] == 0
|
|
p1[1] == 1
|
|
p1[2] == 4
|
|
p1[3] == 9</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>7.22.3.4 The malloc function (p: 349)</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>7.20.3.3 The malloc function (p: 314)</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>4.10.3.3 The malloc 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"></table>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|