137 lines
9.7 KiB
HTML
137 lines
9.7 KiB
HTML
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<title>std::function<R(Args...)>::operator()</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_functional_function_operator 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::function<R(Args...)>::</span>operator()</h1>
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<div id="bodyContent">
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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>‎ | <a href="cpp-utility-functional-function.html">function</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">R operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> Args... <span class="me1">args</span> <span class="br0">)</span> <span class="kw4">const</span><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-rev t-since-cxx11">(C++11 起)</span></td>
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<p>以参数 <code>args</code> 调用存储的可调用函数目标。</p>
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<p>等效于进行 <span class="t-c"><span class="mw-geshi cpp source-cpp">INVOKE<span class="sy1"><</span>R<span class="sy1">></span><span class="br0">(</span>f, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">)</span></span></span> ，其中 <code>f</code> 是 <code>*this</code> 的目标对象，且 <code>INVOKE</code> 是描述于<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> 的操作。</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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<table class="t-par-begin">
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<td>args</td>
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<td>-</td>
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<td>传递给存储的可调用函数目标的参数</td>
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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>若 <code>R</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 则为无。否则为存储的可调用对象的调用返回值。</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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<ul>
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<li>若不存储可调用函数目标，即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="sy2">*</span>this <span class="sy1">==</span> <span class="kw2">true</span></span></span> ，则抛出 <span class="t-lc"><a href="cpp-utility-functional-bad_function_call.html">std::bad_function_call</a></span> 。</li>
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</ul>
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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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<p>下列示例展示能如何将 <span class="t-lc"><a href="cpp-utility-functional-function.html">std::function</a></span> 按值传递给另一函数。而且，它演示 <span class="t-lc"><a href="cpp-utility-functional-function.html">std::function</a></span> 能如何存储 lambda 。</p>
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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="kw4">void</span> call<span class="br0">(</span><a href="cpp-utility-functional-function.html"><span class="kw1059">std::<span class="me2">function</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span> f<span class="br0">)</span> <span class="co1">// 能按值传递</span>
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<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> f<span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> normal_function<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> <span class="nu0">42</span><span class="sy4">;</span>
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<span class="br0">}</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="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
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<a href="cpp-utility-functional-function.html"><span class="kw1059">std::<span class="me2">function</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">></span> f <span class="sy1">=</span> <span class="br0">[</span><span class="sy3">&</span>n<span class="br0">]</span><span class="br0">(</span><span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> n<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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call<span class="br0">(</span>f<span class="br0">)</span><span class="sy4">;</span>
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n <span class="sy1">=</span> <span class="nu0">2</span><span class="sy4">;</span>
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call<span class="br0">(</span>f<span class="br0">)</span><span class="sy4">;</span>
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f <span class="sy1">=</span> normal_function<span class="sy4">;</span>
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call<span class="br0">(</span>f<span class="br0">)</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">1
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2
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42</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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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-move_only_function-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>调用目标<br />
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<span class="t-mark">(<code>std::move_only_function<R(Args...) <i>cv</i> <i>ref</i> noexcept(<i>noex</i>)></code> 的公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-functional-reference_wrapper-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
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</div>
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</td>
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<td>调用其所存储的函数<br />
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<span class="t-mark">(<code>std::reference_wrapper<T></code> 的公开成员函数)</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-bad_function_call.html"><span class="t-lines"><span>bad_function_call</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>调用空的 <span class="t-lc"><a href="cpp-utility-functional-function.html">std::function</a></span> 时抛出的异常<br />
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<span class="t-mark">(类)</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-invoke.html"><span class="t-lines"><span>invoke</span><span>invoke_r</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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</div>
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</td>
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<td>以给定实参<span class="t-rev-inl t-since-cxx23"><span>和可能指定的返回类型</span> <span><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></span></span>调用任意<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> 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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</body>
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