132 lines
9.1 KiB
HTML
132 lines
9.1 KiB
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>free</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_memory_free 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">free</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-memory.html">memory</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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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><stdlib.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 class="t-dcl-nopad">
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<div><span class="mw-geshi c source-c"><span class="kw4">void</span> free<span class="br0">(</span> <span class="kw4">void</span><span class="sy2">*</span> ptr <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 class="t-dcl-nopad"></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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<td></td>
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<p>解分配之前由 <span class="t-lc"><a href="c-memory-malloc.html">malloc()</a></span> 、 <span class="t-lc"><a href="c-memory-calloc.html">calloc()</a></span> <span class="t-rev-inl t-since-c11"><span>、 <span class="t-lc">aligned_alloc()</span></span> <span><span class="t-mark-rev t-since-c11">(C11 起)</span></span></span> 或 <span class="t-lc"><a href="c-memory-realloc.html">realloc()</a></span> 分配的空间。</p>
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<p>若 <code>ptr</code> 为空指针，则函数不进行操作。</p>
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<p>若 <code>ptr</code> 的值不等于之前从 <span class="t-lc"><a href="c-memory-malloc.html">malloc()</a></span> 、 <span class="t-lc"><a href="c-memory-calloc.html">calloc()</a></span> 、 <span class="t-lc"><a href="c-memory-realloc.html">realloc()</a></span> <span class="t-rev-inl t-since-c11"><span>或 <span class="t-lc">aligned_alloc()</span></span> <span><span class="t-mark-rev t-since-c11">(C11 起)</span></span></span> 返回的值，则行为未定义。</p>
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<p>若 <code>ptr</code> 所指代的内存区域已经被解分配，则行为未定义，即是说已经以<code>ptr</code> 为参数调用 <code>free()</code> 或 <span class="t-lc"><a href="c-memory-realloc.html">realloc()</a></span> ，而且没有后继的 <span class="t-lc"><a href="c-memory-malloc.html">malloc()</a></span> 、 <span class="t-lc"><a href="c-memory-calloc.html">calloc()</a></span> 或 <span class="t-lc"><a href="c-memory-realloc.html">realloc()</a></span> 调用以 <code>ptr</code> 为结果。</p>
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<p>若在 <code>free()</code> 返回后通过指针 <code>ptr</code> 访问内存，则行为未定义（除非另一个分配函数恰好返回等于 <code>ptr</code> 的值）。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-c11">
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<td>
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<p><code>free</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>
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<p>令 <span class="t-lc"><strong class="selflink">free</strong></span> 解分配内存区域的调用，<i>同步于</i>任何令分配函数分配相同或部分相同区域的后续调用。这种同步出现于任何解分配函数所做的内存访问后，和任何分配函数所做的内存访问前。所有操作每块特定内存区域的分配及解分配函数拥有单独全序。</p>
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</td>
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<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
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</tr>
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</table>
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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>ptr</td>
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<td>-</td>
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<td>指向要解分配的内存的指针</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>（无）</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>此函数接收空指针（并对其不处理）以减少特例的数量。不管分配成功与否，分配函数返回的指针都能传递给 <code>free()</code> 。</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">#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">int</span> <span class="sy2">*</span>p1 <span class="sy1">=</span> <a href="c-memory-malloc.html"><span class="kw403">malloc</span></a><span class="br0">(</span><span class="nu0">10</span><span class="sy2">*</span><span class="kw4">sizeof</span> <span class="sy2">*</span>p1<span class="br0">)</span><span class="sy4">;</span>
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free<span class="br0">(</span>p1<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 每一个分配的指针都要释放</span>
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<span class="kw4">int</span> <span class="sy2">*</span>p2 <span class="sy1">=</span> <a href="c-memory-calloc.html"><span class="kw404">calloc</span></a><span class="br0">(</span><span class="nu0">10</span>, <span class="kw4">sizeof</span> <span class="sy2">*</span>p2<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> <span class="sy2">*</span>p3 <span class="sy1">=</span> <a href="c-memory-realloc.html"><span class="kw405">realloc</span></a><span class="br0">(</span>p2, <span class="nu0">1000</span><span class="sy2">*</span><span class="kw4">sizeof</span> <span class="sy2">*</span>p3<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>p3<span class="br0">)</span> <span class="co1">// p3 非空表示 p2 被 realloc 释放</span>
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free<span class="br0">(</span>p3<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">else</span> <span class="co1">// p3 为空表示 p2 未被释放</span>
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free<span class="br0">(</span>p2<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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</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>7.22.3.3 The free function (p: 348)</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>7.20.3.2 The free function (p: 313)</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>4.10.3.2 The free 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"></table>
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</div>
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</div>
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<div class="visualClear"></div>
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</body>
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</html>
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