146 lines
9.7 KiB
HTML
146 lines
9.7 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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<title>std::unary_function</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_functional_unary_function 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>unary_function</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-functional.html">functional</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-functional.html"><functional></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span> ArgumentType, <span class="kw1">typename</span> ResultType<span class="sy1">></span><br />
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<span class="kw1">struct</span> unary_function<span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark">(C++11 中弃用)</span><br />
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<span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></td>
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<p><code>unary_function</code> 是用于创建拥有一个参数的函数的基类。</p>
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<p><code>unary_function</code> 不定义 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="br0">(</span><span class="br0">)</span></span></span> ；它期待导出类定义此运算符。 <code>unary_function</code> 只提供二个类型—— <code>argument_type</code> 和 <code>result_type</code> ——为模板形参所定义。</p>
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<p>一些标准库函数适配器，如 <span class="t-lc"><a href="cpp-utility-functional-not1.html">std::not1</a></span> ，要求它们适配的函数对象已定义某些类型； <span class="t-lc"><a href="cpp-utility-functional-not1.html">std::not1</a></span> 要求要适配的函数对象拥有名为 <code>argument_type</code> 的类型。从 <code>unary_function</code> 导出函数对象是令它们与那些适配器兼容的简易方式。</p>
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<p><code>unary_function</code> 在 C++11 中被弃用。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>类型</td>
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<td>定义</td>
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<td><code>argument_type</code></td>
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<td><code>ArgumentType</code></td>
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<tr class="t-dsc">
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<td><code>result_type</code></td>
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<td><code>ResultType</code></td>
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</tr>
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</table>
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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 <algorithm></span>
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<span class="co2">#include <functional></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <vector></span>
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<span class="kw1">struct</span> less_than_7 <span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">unary_function</span><span class="sy1"><</span><span class="kw4">int</span>, <span class="kw4">bool</span><span class="sy1">></span>
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<span class="br0">{</span>
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<span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <span class="kw1">return</span> i <span class="sy1"><</span> <span class="nu0">7</span><span class="sy4">;</span> <span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</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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<a href="cpp-container-vector.html"><span class="kw1268">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> v<span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1"><</span> <span class="nu0">10</span><span class="sy4">;</span> <span class="sy2">++</span>i<span class="br0">)</span> v.<span class="me1">push_back</span><span class="br0">(</span>i<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-algorithm-count_if.html"><span class="kw1570">std::<span class="me2">count_if</span></span></a><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <a href="cpp-utility-functional-not1.html"><span class="kw1050">std::<span class="me2">not1</span></span></a><span class="br0">(</span>less_than_7<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="coMULTI">/* C++11 解法：
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// 用某方法转型到 std::function<bool (int)> ——即使以 lambda
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std::cout << std::count_if(v.begin(), v.end(),
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std::not1(std::function<bool (int)>([](int i){ return i < 7; }))
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);
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*/</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">3</pre></div>
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</div>
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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="cpp-utility-functional-function.html"><span class="t-lines"><span>function</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></div>
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</div>
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</td>
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<td>包装具有指定函数调用签名的任意可复制构造类型的可调用对象<br />
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<span class="t-mark">(类模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-ptr_fun.html"><span class="t-lines"><span>ptr_fun</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-deprecated-cxx11">(C++11 中弃用)</span><span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></span></span></div>
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</div>
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</td>
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<td>从函数指针创建与适配器兼容的函数对象包装器<br />
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<span class="t-mark">(函数模板)</span></td>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-pointer_to_unary_function.html"><span class="t-lines"><span>pointer_to_unary_function</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-deprecated-cxx11">(C++11 中弃用)</span></span><span><span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></span></span></div>
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</div>
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</td>
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<td>适配器兼容的包装，用于包装一元函数的指针<br />
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<span class="t-mark">(类模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-binary_function.html"><span class="t-lines"><span>binary_function</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-deprecated-cxx11">(C++11 中弃用)</span></span><span><span class="t-mark-rev t-until-cxx17">(C++17 中移除)</span></span></span></div>
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</div>
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</td>
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<td>与适配器兼容的二元函数基类<br />
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<span class="t-mark">(类模板)</span></td>
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</table>
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</div>
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<div class="visualClear"></div>
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</body>
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