45 lines
6.7 KiB
HTML
45 lines
6.7 KiB
HTML
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<title>C++ 具名要求：谓词 (Predicate)</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">C++ 具名要求：</span><span style="font-style:italic">谓词</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Predicate)</span></h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-named_req.html">named req</a></span></div>
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<p><strong class="selflink"><span style="font-style:italic">谓词</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Predicate)</span></strong> 要求描述了返回可作为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> 测试的值的<a href="cpp-named_req-Callable.html"><span style="font-style:italic">可调用</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Callable)</span></a> 体。</p>
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<p><strong class="selflink"><span style="font-style:italic">谓词</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Predicate)</span></strong> 常与接收输入数据（单独的对象/容器）和谓词的算法一起使用，它会针对输入数据进行调用以决定进一步的动作。C++ 标准库中的一些使用谓词的例子有：</p>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-all_any_none_of.html"><span class="kw1565">std::<span class="me2">all_of</span></span></a></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-all_any_none_of.html"><span class="kw1566">std::<span class="me2">any_of</span></span></a></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-all_any_none_of.html"><span class="kw1567">std::<span class="me2">none_of</span></span></a></span></span> 接收一组元素和一个谓词为其输入。在每个单独的输入元素上调用谓词，并且当谓词分别对全部/任一/无元素返回 true 时返回 true。</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-find_if_not.html"><span class="kw1575">std::<span class="me2">find_if</span></span></a></span></span> 接受元素的序列和一个谓词。返回序列中首个谓词对其返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 的元素。</li>
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<p><span style="font-size:0.7em; line-height:130%">上面给出的算法设施描述是简陋的，并且有意地简要解释<strong class="selflink"><span style="font-style:italic">谓词</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Predicate)</span></strong> 。对于详细信息可查阅各自的页面。</span></p>
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<p>换言之，若算法接收一个<strong class="selflink"><span style="font-style:italic">谓词</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Predicate)</span></strong> <code>pred</code> 和一个迭代器 <code>first</code>，则它应该能经由类似 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">if</span><span class="br0">(</span>pred<span class="br0">(</span><span class="sy2">*</span>first<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>...<span class="br0">}</span></span></span> 的构造，测试迭代器 <code>first</code> 所指向的类型。</p>
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<p>函数对象 <code>pred</code> 不应当通过解引用的迭代器运用任何非 const 函数。此函数对象可以是函数指针，或者拥有适合的函数调用运算符的类型的对象。</p>
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<h3><span class="mw-headline" id=".E8.A6.81.E6.B1.82">要求</span></h3>
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<li><a href="cpp-named_req-FunctionObject.html"><span style="font-style:italic">函数对象</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(FunctionObject)</span></a></li>
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<td class="mbox-text" style="">本节未完成<br />
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原因：更好地描述实际要求</td>
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