100 lines
9.9 KiB
HTML
100 lines
9.9 KiB
HTML
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<title>std::free</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_c_free skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>free</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-memory.html">memory</a>‎ | <a href="cpp-memory-c.html">c</a></span></div>
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<table class="t-dcl-begin">
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<div>定义于头文件 <code><a href="cpp-header-cstdlib.html"><cstdlib></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><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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<p>解分配先前由 <span class="t-lc"><a href="cpp-memory-c-malloc.html">std::malloc()</a></span> 、 <span class="t-lc"><a href="cpp-memory-c-calloc.html">std::calloc()</a></span> <span class="t-rev-inl t-since-cxx17"><span>、 <span class="t-lc"><a href="cpp-memory-c-aligned_alloc.html">std::aligned_alloc</a></span></span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span> 或 <span class="t-lc"><a href="cpp-memory-c-realloc.html">std::realloc()</a></span> 分配的内存空间。</p>
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<p>若 <code>ptr</code> 是空指针，则函数不做任何事。</p>
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<p>若 <code>ptr</code> 的值不等于先前 <span class="t-lc"><a href="cpp-memory-c-malloc.html">std::malloc()</a></span> 、 <span class="t-lc"><a href="cpp-memory-c-calloc.html">std::calloc()</a></span> <span class="t-rev-inl t-since-cxx17"><span>、 <span class="t-lc"><a href="cpp-memory-c-aligned_alloc.html">std::aligned_alloc</a></span></span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span> 或 <span class="t-lc"><a href="cpp-memory-c-realloc.html">std::realloc()</a></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被解分配，即已以 <code>ptr</code> 为参数掉调用 <code>std::free()</code> 或 <span class="t-lc"><a href="cpp-memory-c-realloc.html">std::realloc()</a></span> ，且无对 <span class="t-lc"><a href="cpp-memory-c-malloc.html">std::malloc()</a></span> 、 <span class="t-lc"><a href="cpp-memory-c-calloc.html">std::calloc()</a></span> <span class="t-rev-inl t-since-cxx17"><span>、 <span class="t-lc"><a href="cpp-memory-c-aligned_alloc.html">std::aligned_alloc</a></span></span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span> 或 <span class="t-lc"><a href="cpp-memory-c-realloc.html">std::realloc()</a></span> 产生等于之前 <code>ptr</code> 的指针，则行为未定义。</p>
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<p>若在 <code>std::free()</code> 返回后，通过指针 <code>ptr</code> 访问（除非另一分配函数恰好产生等于 <code>ptr</code> 的指针值），则行为未定义。</p>
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<td>
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<p>要求下列函数是线程安全的：</p>
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<ul>
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<li><a href="cpp-memory-new-operator_new.html"><tt>operator new</tt></a> 及 <a href="cpp-memory-new-operator_delete.html"><tt>operator delete</tt></a> 的库版本</li>
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<li>全局 <a href="cpp-memory-new-operator_new.html"><tt>operator new</tt></a> 与 <a href="cpp-memory-new-operator_delete.html"><tt>operator delete</tt></a> 的用户替换版本</li>
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<li><span class="t-lc"><a href="cpp-memory-c-calloc.html">std::calloc</a></span> 、 <span class="t-lc"><a href="cpp-memory-c-malloc.html">std::malloc</a></span> 、 <span class="t-lc"><a href="cpp-memory-c-realloc.html">std::realloc</a></span> <span class="t-rev-inl t-since-cxx17"><span>、 <span class="t-lc"><a href="cpp-memory-c-aligned_alloc.html">std::aligned_alloc</a></span></span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span> 、 <span class="t-lc"><strong class="selflink">std::free</strong></span></li>
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</ul>
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<p>对这些分配或解分配特定存储单元的函数调用以单独全序出现，并且在此顺序中，每个解分配调用<a href="cpp-atomic-memory_order.html">先发生于</a>下个分配（若存在）。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 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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<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.E6.84.8F">注意</span></h3>
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<p>此函数接受空指针（不做任何事）以减少特殊情况的总数。无论分配是否成功，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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <cstdlib></span>
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<span class="kw4">int</span> main<span class="br0">(</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> <span class="br0">(</span><span class="kw4">int</span><span class="sy2">*</span><span class="br0">)</span><a href="cpp-memory-c-malloc.html"><span class="kw759">std::<span class="me2">malloc</span></span></a><span class="br0">(</span><span class="nu0">10</span><span class="sy2">*</span>sizeof <span class="sy2">*</span>p1<span class="br0">)</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">free</span><span class="br0">(</span>p1<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 每个分配的指针都必须释放</span>
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<span class="kw4">int</span><span class="sy2">*</span> p2 <span class="sy1">=</span> <span class="br0">(</span><span class="kw4">int</span><span class="sy2">*</span><span class="br0">)</span><a href="cpp-memory-c-calloc.html"><span class="kw761">std::<span class="me2">calloc</span></span></a><span class="br0">(</span><span class="nu0">10</span>, sizeof <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> <span class="br0">(</span><span class="kw4">int</span><span class="sy2">*</span><span class="br0">)</span><a href="cpp-memory-c-realloc.html"><span class="kw762">std::<span class="me2">realloc</span></span></a><span class="br0">(</span>p2, <span class="nu0">1000</span><span class="sy2">*</span>sizeof <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 为 std::realloc 所释放</span>
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std<span class="sy4">::</span><span class="me2">free</span><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 空表示 p2 未被释放</span>
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std<span class="sy4">::</span><span class="me2">free</span><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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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div class="visualClear"></div>
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