72 lines
9.2 KiB
HTML
72 lines
9.2 KiB
HTML
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<title>std::inout_ptr_t<Smart,Pointer,Args...>::operator Pointer*, std::inout_ptr_t<Smart,Pointer,Args...>::operator void**</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::inout_ptr_t<Smart,Pointer,Args...>::</span>operator Pointer*, <span style="font-size:0.7em; line-height:130%">std::inout_ptr_t<Smart,Pointer,Args...>::</span>operator void**</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-inout_ptr_t.html">inout ptr t</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">operator Pointer<span class="sy2">*</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">operator <span class="kw4">void</span><span class="sy2">**</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></td>
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<p>暴露 <code>Pointer</code> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 对象的地址给一般会释放其值所表示的所有权然后重初始化它的外来函数。</p>
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<div class="t-li1"><span class="t-li">1)</span> 转换 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 为存储的 <code>Pointer</code> 对象的地址。</div>
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<div class="t-li1"><span class="t-li">2)</span> 转换 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 对象的地址。此转换函数仅若 <code>Pointer</code> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 不同才参与重载决议，而若 <code>Pointer</code> 不是指针类型则程序非良构。<br />
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<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 对象的初值等于存储的 <code>Pointer</code> 对象的值转换到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> ，而任何对它的修改影响用于<a href="cpp-memory-inout_ptr_t-~inout_ptr_t.html">析构函数</a>的 <code>Pointer</code> 值。在 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的生存期外访问该 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 拥有未定义行为。</div>
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<p>一旦在一个 <code>inout_ptr_t</code> 对象上调用了此二转换函数之一，则不应当调用另一个，否则行为未定义。</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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<p>（无）</p>
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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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<div class="t-li1"><span class="t-li">1)</span> 存储的 <code>Pointer</code> 对象的地址。</div>
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<div class="t-li1"><span class="t-li">2)</span> 满足前述要求的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 对象的地址。</div>
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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>若返回值所指向的对象未被写入，则它等于适配的 <code>Smart</code> 对象在构造前持有的值。</p>
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<p>常见实现上，每个作为指针类型的 <code>Pointer</code> 对象表示均与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 的兼容，从而这些实现常在 <code>Pointer</code> 对象的存储内存储该 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 对象，不需要额外存储：</p>
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<ul>
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<li>若实现启用基于类型的别名分析（依赖<a href="cpp-language-reinterpret_cast.html#.E7.B1.BB.E5.9E.8B.E5.88.AB.E5.90.8D.E5.8C.96">严格别名化规则</a>），则可以使用正确对齐的 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">byte</span><span class="br0">[</span>sizeof<span class="br0">(</span><span class="kw4">void</span><span class="sy2">*</span><span class="br0">)</span><span class="br0">]</span></span></span> 成员子对象，而两个转换函数都返回在该数组内<a href="cpp-language-object.html#.E5.AF.B9.E8.B1.A1.E5.88.9B.E5.BB.BA">隐式创建</a>的对象的地址。</li>
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<li>否则，可将 <code>Pointer</code> 成员子对象用于两个转换函数，而 <span class="t-v">(2)</span> 可以直接返回 <a href="cpp-language-reinterpret_cast.html"><tt>reinterpret_cast</tt></a> 成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">**</span></span></span> 的其地址。</li>
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<p>若 <code>Pointer</code> 是对象表示与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 的不兼容的指针类型，则可能需要额外的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> 标志记录是否调用了 <span class="t-v">(1)</span> （或 <span class="t-v">(2)</span> ）。</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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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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