140 lines
11 KiB
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140 lines
11 KiB
HTML
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<title>std::bind1st, std::bind2nd</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_functional_bind12 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>bind1st, <span style="font-size:0.7em; line-height:130%">std::</span>bind2nd</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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<table class="t-dcl-begin">
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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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<td></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> F, <span class="kw1">class</span> T <span class="sy1">></span><br />
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std<span class="sy4">::</span><span class="me2">binder1st</span><span class="sy1"><</span>F<span class="sy1">></span> bind1st<span class="br0">(</span> <span class="kw4">const</span> F<span class="sy3">&</span> f, <span class="kw4">const</span> T<span class="sy3">&</span> x <span class="br0">)</span><span class="sy4">;</span></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> F, <span class="kw1">class</span> T <span class="sy1">></span><br />
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std<span class="sy4">::</span><span class="me2">binder2nd</span><span class="sy1"><</span>F<span class="sy1">></span> bind2nd<span class="br0">(</span> <span class="kw4">const</span> F<span class="sy3">&</span> f, <span class="kw4">const</span> T<span class="sy3">&</span> x <span class="br0">)</span><span class="sy4">;</span></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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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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<p>绑定给定参数 <code>x</code> 到给定二元函数对象 <code>f</code> 的第一或第二参变量。即，在产生的包装器内存储 <code>x</code> ，若调用它，则将 <code>x</code> 传递为 <code>f</code> 的第一或第二参数。</p>
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<div class="t-li1"><span class="t-li">1)</span> 绑定 <code>f</code> 的第一参数到 <code>x</code> 。等效地调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">binder1st</span><span class="sy1"><</span>F<span class="sy1">></span><span class="br0">(</span>f, <span class="kw1">typename</span> F<span class="sy4">::</span><span class="me2">first_argument_type</span><span class="br0">(</span>x<span class="br0">)</span><span class="br0">)</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 绑定 <code>f</code> 的第二参数到 <code>x</code> 。等效地调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">binder2nd</span><span class="sy1"><</span>F<span class="sy1">></span><span class="br0">(</span>f, <span class="kw1">typename</span> F<span class="sy4">::</span><span class="me2">second_argument_type</span><span class="br0">(</span>x<span class="br0">)</span><span class="br0">)</span></span></span> 。</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<td>f</td>
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<td>-</td>
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<td>指向要绑定参数到的函数的指针</td>
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</tr>
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<tr class="t-par">
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<td>x</td>
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<td>-</td>
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<td>绑定到 <code>f</code> 的参数</td>
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</tr>
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</table>
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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>包装 <code>f</code> 和 <code>x</code> 的函数对象。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>可能抛出实现定义的异常。</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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<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 <iomanip></span>
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<span class="co2">#include <algorithm></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 <cstddef></span>
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<span class="co2">#include <vector></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="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">></span> a <span class="sy1">=</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="sy4">;</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">></span> r<span class="br0">(</span>a.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</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> <span class="co1">// C++20 起使用 std::numbers::pi</span>
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<a href="cpp-algorithm-transform.html"><span class="kw1589">std::<span class="me2">transform</span></span></a><span class="br0">(</span>a.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, a.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, r.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>,
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std<span class="sy4">::</span><span class="me2">bind1st</span><span class="br0">(</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><span class="br0">(</span><span class="br0">)</span>, pi <span class="sy2">/</span> <span class="nu0">180</span>.<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 等价的 lambda 为： [pi](double a){ return a*pi / 180.; });</span>
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<span class="kw1">for</span><span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> n <span class="sy1"><</span> a.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="sy2">++</span>n<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> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">3</span><span class="br0">)</span> <span class="sy1"><<</span> a<span class="br0">[</span>n<span class="br0">]</span> <span class="sy1"><<</span> <span class="st0">"° = "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-fixed.html"><span class="kw1784">std::<span class="me2">fixed</span></span></a> <span class="sy1"><<</span> r<span class="br0">[</span>n<span class="br0">]</span>
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<span class="sy1"><<</span> <span class="st0">" rad<span class="es1">\n</span>"</span> <span class="sy1"><<</span> <a href="cpp-io-manip-fixed.html"><span class="kw1787">std::<span class="me2">defaultfloat</span></span></a><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">
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0° = 0.000000 rad
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30° = 0.523599 rad
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45° = 0.785398 rad
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60° = 1.047198 rad
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90° = 1.570796 rad
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180° = 3.141593 rad</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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<table class="t-dsc-begin">
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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-binder12.html"><span class="t-lines"><span>binder1st</span><span>binder2nd</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>持有一个二元函数及其实参之一的函数对象<br />
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<span class="t-mark">(类模板)</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-bind_front.html"><span class="t-lines"><span>bind_front</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>按顺序绑定一定数量的参数到函数对象<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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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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