162 lines
9.6 KiB
HTML
162 lines
9.6 KiB
HTML
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<title>std::atomic<T>::fetch_sub</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_atomic_atomic_fetch_sub 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::atomic<T>::</span>fetch_sub</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-atomic.html">atomic</a>‎ | <a href="cpp-atomic-atomic.html">atomic</a></span></div>
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<div>仅为 <code>atomic<<i>Integral</i>></code><span class="t-mark-rev t-since-cxx11">(C++11)</span> 与 <code>atomic<<i>Floating</i>></code><span class="t-mark-rev t-since-cxx20">(C++20)</span> 模板特化的成员</div>
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<td rowspan="142">(1)</td>
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<div><span class="mw-geshi cpp source-cpp">T fetch_sub<span class="br0">(</span> T arg,<br />
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<a href="cpp-atomic-memory_order.html"><span class="kw2092">std::<span class="me2">memory_order</span></span></a> order <span class="sy1">=</span> <a href="cpp-atomic-memory_order.html"><span class="kw2098">std::<span class="me2">memory_order_seq_cst</span></span></a> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">T fetch_sub<span class="br0">(</span> T arg,<br />
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<a href="cpp-atomic-memory_order.html"><span class="kw2092">std::<span class="me2">memory_order</span></span></a> order <span class="sy1">=</span> <a href="cpp-atomic-memory_order.html"><span class="kw2098">std::<span class="me2">memory_order_seq_cst</span></span></a> <span class="br0">)</span> <span class="kw4">volatile</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<div>仅为 <code>atomic<T*></code> 模板特化的成员</div>
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<td rowspan="142">(2)</td>
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<div><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span> fetch_sub<span class="br0">(</span> <a href="cpp-types-ptrdiff_t.html"><span class="kw101">std::<span class="me2">ptrdiff_t</span></span></a> arg,<br />
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<a href="cpp-atomic-memory_order.html"><span class="kw2092">std::<span class="me2">memory_order</span></span></a> order <span class="sy1">=</span> <a href="cpp-atomic-memory_order.html"><span class="kw2098">std::<span class="me2">memory_order_seq_cst</span></span></a> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">T<span class="sy2">*</span> fetch_sub<span class="br0">(</span> <a href="cpp-types-ptrdiff_t.html"><span class="kw101">std::<span class="me2">ptrdiff_t</span></span></a> arg,<br />
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<a href="cpp-atomic-memory_order.html"><span class="kw2092">std::<span class="me2">memory_order</span></span></a> order <span class="sy1">=</span> <a href="cpp-atomic-memory_order.html"><span class="kw2098">std::<span class="me2">memory_order_seq_cst</span></span></a> <span class="br0">)</span> <span class="kw4">volatile</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<p>以值和 <code>arg</code> 的算术减法结果原子地替换当前值。操作是读修改写操作。按照 <code>order</code> 的值影响内存。</p>
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<p>对于有符号 <code>Integral</code> 类型，定义算术为使用补码表示。无未定义结果。</p>
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<p>对于 <code>T*</code> 类型，结果可能是未定义地址，但此外操作不会有未定义行为。若 <code>T</code> 不是对象类型则程序为谬构。</p>
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<p>对于浮点类型，有影响的<a href="cpp-numeric-fenv.html">浮点环境</a>可能异于调用方线程的浮点环境。操作不必遵循对应的 <span class="t-lc"><a href="cpp-types-numeric_limits.html">std::numeric_limits</a></span> 特性，但鼓励这么做。若结果不是其类型所能表示的值，则结果未指定，但此外操作不会有未定义行为。</p>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-atomic-atomic.html"><span class="kw2066">std::<span class="me2">atomic</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">is_always_lock_free</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 则 volatile 限定版本被弃用。</p>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<td>arg</td>
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<td>-</td>
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<td>算术减法的另一参数</td>
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<td>order</td>
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<td>-</td>
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<td>强制的内存顺序制约</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><code>*this</code> 的<a href="cpp-atomic-memory_order.html#.E4.BF.AE.E6.94.B9.E9.A1.BA.E5.BA.8F">修改顺序</a>中立即前趋此函数效果的值。</p>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P0558R1">P0558R1</a></td>
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<td>C++11</td>
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<td>曾容许指向 <i>cv</i> void 或函数的指针</td>
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<td>使之为谬构</td>
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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="t-dsc-member-div">
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<div><a href="cpp-atomic-atomic_fetch_sub.html"><span class="t-lines"><span>atomic_fetch_sub</span><span>atomic_fetch_sub_explicit</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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<td>从原子对象减去非原子值，并获得原子对象的先前值<br />
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<span class="t-mark">(函数模板)</span></td>
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