103 lines
6.8 KiB
HTML
103 lines
6.8 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<title>atomic_fetch_sub, atomic_fetch_sub_explicit</title>
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<link rel="stylesheet" href="ext.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_atomic_atomic_fetch_sub 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">atomic_fetch_sub, atomic_fetch_sub_explicit</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-atomic.html">atomic</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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<div>定义于头文件 <code><stdatomic.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 t-since-c11">
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<div><span class="mw-geshi c source-c">C atomic_fetch_sub<span class="br0">(</span> <span class="kw4">volatile</span> A<span class="sy2">*</span> obj, M arg <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
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<tr class="t-dcl t-since-c11">
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<td>
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<div><span class="mw-geshi c source-c">C atomic_fetch_sub_explicit<span class="br0">(</span> <span class="kw4">volatile</span> A<span class="sy2">*</span> obj, M arg, <a href="c-atomic-memory_order.html"><span class="kw910">memory_order</span></a> order <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</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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<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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</tbody>
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</table>
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<p>以 <code>*obj</code> 的旧值减去 <code>arg</code> 的结果原子地替换 <code>obj</code> 的所指向值，并返回 <code>*obj</code> 先前保有的值。此操作是读修改写操作。第一版本按照 <span class="t-lc"><a href="c-atomic-memory_order.html">memory_order_seq_cst</a></span> 排序内存访问，第二版本按照 <code>order</code> 排序内存访问。</p>
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<p>这是为所有<a href="c-language-atomic.html">原子对象类型</a> <code>A</code> 定义的<a href="c-language-generic.html">泛型函数</a>。参数为指向 volatile 原子对象的指针，以接受非 volatile 与 <a href="c-language-volatile.html">volatile</a> （例如内存映射 I/O ）的原子对象，而 volatile 语义在应用此操作时保留。 若 <code>A</code> 为原子整数类型则 <code>M</code> 是对应 <code>A</code> 的非原子类型，或若 <code>A</code> 为原子指针类型则 <code>M</code> 为 <span class="t-lc"><a href="c-types-ptrdiff_t.html">ptrdiff_t</a></span> 。</p>
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<p>泛型函数名是宏或是声明有外部链接的标识符是未指定的。若为访问实际函数压制宏定义（例如像 <span class="t-c"><span class="mw-geshi c source-c"><span class="br0">(</span>atomic_fetch_sub<span class="br0">)</span><span class="br0">(</span>...<span class="br0">)</span></span></span> 这样加括号），或程序定义拥有泛型函数名的外部标识符，则行为未定义。</p>
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<p>对于有符号整数类型，定义算术为使用补码表示。无未定义结果。对于指针类型，结果可能是未定义地址，但运算不会另有未定义行为。</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>obj</td>
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<td>-</td>
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<td>指向要修改的原子对象的指针</td>
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</tr>
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<tr class="t-par">
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<td>arg</td>
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<td>-</td>
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<td>要从存储于原子对象中的值减去的值</td>
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</tr>
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<tr class="t-par">
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<td>order</td>
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<td>-</td>
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<td>此操作的内存同步顺序：容许所有值</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><code>obj</code> 所指向的原子对象先前保有的值。</p>
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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>7.17.7.5 The atomic_fetch and modify generic functions (p: 284-285)</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">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="c-atomic-atomic_fetch_add.html"><span class="t-lines"><span>atomic_fetch_add</span><span>atomic_fetch_add_explicit</span></span></a></div>
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<div><span class="t-lines"><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>原子加法<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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</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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