140 lines
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140 lines
13 KiB
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<title>std::binder1st, std::binder2nd</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>binder1st, <span style="font-size:0.7em; line-height:130%">std::</span>binder2nd</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">class</span> Fn <span class="sy1">></span><br /></span>
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<p><span class="kw1">class</span> binder1st <span class="sy4">:</span> <span class="kw1">public</span> <a href="cpp-utility-functional-unary_function.html"><span class="kw1125">std::<span class="me2">unary_function</span></span></a><span class="sy1"><</span><span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">second_argument_type</span>,<br />
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<span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">result_type</span><span class="sy1">></span> <span class="br0">{</span><br />
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<span class="kw1">protected</span><span class="sy4">:</span><br />
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<br />
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Fn op<span class="sy4">;</span><br />
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<span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">first_argument_type</span> value<span class="sy4">;</span><br />
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<br />
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<span class="kw1">public</span><span class="sy4">:</span><br />
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<br />
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binder1st<span class="br0">(</span><span class="kw4">const</span> Fn<span class="sy3">&</span> fn,<br />
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<span class="kw4">const</span> <span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">first_argument_type</span><span class="sy3">&</span> value<span class="br0">)</span><span class="sy4">;</span><br />
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<br />
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<span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">result_type</span><br />
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operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> <span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">second_argument_type</span><span class="sy3">&</span> x<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span><br />
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<br />
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<span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">result_type</span><br />
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operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">second_argument_type</span><span class="sy3">&</span> x<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</span><span class="sy4">;</span></div>
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</td>
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<td>(1)</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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Fn <span class="sy1">></span><br /></span>
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<p><span class="kw1">class</span> binder2nd <span class="sy4">:</span> <span class="kw1">public</span> unary_function<span class="sy1"><</span><span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">first_argument_type</span>,<br />
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<span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">result_type</span><span class="sy1">></span> <span class="br0">{</span><br />
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<span class="kw1">protected</span><span class="sy4">:</span><br />
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Fn op<span class="sy4">;</span><br />
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<span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">second_argument_type</span> value<span class="sy4">;</span><br />
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<span class="kw1">public</span><span class="sy4">:</span><br />
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binder2nd<span class="br0">(</span><span class="kw4">const</span> Fn<span class="sy3">&</span> fn,<br />
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<span class="kw4">const</span> <span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">second_argument_type</span><span class="sy3">&</span> value<span class="br0">)</span><span class="sy4">;</span><br />
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<br />
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<span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">result_type</span><br />
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operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> <span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">first_argument_type</span><span class="sy3">&</span> x<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span><br />
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<br />
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<span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">result_type</span><br />
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operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw1">typename</span> Fn<span class="sy4">::</span><span class="me2">first_argument_type</span><span class="sy3">&</span> x<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</span><span class="sy4">;</span></div>
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</td>
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<td>(2)</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>绑定实参到二元函数的函数对象。</p>
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<p>在构造时将形参的值传递给对象并在对象中存储。凡在通过 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="br0">(</span><span class="br0">)</span></span></span> 调用函数对象时，均将存储的值作为实参之一传递，将另一实参作为 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="br0">(</span><span class="br0">)</span></span></span> 的实参传递。产生的函数对象是一元函数。</p>
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<div class="t-li1"><span class="t-li">1)</span> 绑定第一参数为在对象构造时给定的值 <code>value</code> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 绑定第二参数为在对象构造时给定的值 <code>value</code> 。</div>
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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 <iostream></span>
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<span class="co2">#include <functional></span>
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<span class="co2">#include <cmath></span>
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<span class="co2">#include <vector></span>
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<span class="kw4">const</span> <span class="kw4">double</span> pi <span class="sy1">=</span> <a href="cpp-numeric-math-acos.html"><span class="kw1337">std::<span class="me2">acos</span></span></a><span class="br0">(</span><span class="sy2">-</span><span class="nu0">1</span><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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<span class="co1">// C++11 中弃用， C++17 中移除</span>
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std<span class="sy4">::</span><span class="me2">binder1st</span><span class="sy1"><</span><a href="cpp-utility-functional-multiplies.html"><span class="kw1031">std::<span class="me2">multiplies</span></span></a><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">>></span> f1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">bind1st</span><span class="br0">(</span>
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<a href="cpp-utility-functional-multiplies.html"><span class="kw1031">std::<span class="me2">multiplies</span></span></a><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span>, pi <span class="sy2">/</span> <span class="nu0">180</span>.<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// C++11 替代</span>
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<span class="kw4">auto</span> f2 <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">double</span> a<span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> a<span class="sy2">*</span>pi<span class="sy2">/</span><span class="nu0">180</span>.<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">double</span> n <span class="sy4">:</span> <span class="br0">{</span><span class="nu0">0</span>, <span class="nu0">30</span>, <span class="nu0">45</span>, <span class="nu0">60</span>, <span class="nu0">90</span>, <span class="nu0">180</span><span class="br0">}</span><span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> n <span class="sy1"><<</span> <span class="st0">" deg = "</span> <span class="sy1"><<</span> f1<span class="br0">(</span>n<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" rad (using binder) "</span>
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<span class="sy1"><<</span> f2<span class="br0">(</span>n<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" rad (using lambda)<span class="es1">\n</span>"</span><span class="sy4">;</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">0 deg = 0 rad (using binder) 0 rad (using lambda)
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30 deg = 0.523599 rad (using binder) 0.523599 rad (using lambda)
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45 deg = 0.785398 rad (using binder) 0.785398 rad (using lambda)
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60 deg = 1.0472 rad (using binder) 1.0472 rad (using lambda)
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90 deg = 1.5708 rad (using binder) 1.5708 rad (using lambda)
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180 deg = 3.14159 rad (using binder) 3.14159 rad (using lambda)</pre></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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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-bind12.html"><span class="t-lines"><span>bind1st</span><span>bind2nd</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>将一个实参绑定到二元函数<br />
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<span class="t-mark">(函数模板)</span></td>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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