265 lines
31 KiB
HTML
265 lines
31 KiB
HTML
<!DOCTYPE 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<title>非静态成员函数</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_language_member_functions skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading">非静态成员函数</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-language.html">language</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<p>非静态成员函数是在类的<a href="cpp-language-class.html">成员说明</a>中不带 <a href="cpp-language-static.html"><code>static</code></a> 或 <a href="cpp-language-friend.html"><code>friend</code></a> 说明符声明的函数。（这些关键词的效果见<a href="cpp-language-static.html#.E9.9D.99.E6.80.81.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">静态成员函数</a>与<a href="cpp-language-friend.html">友元声明</a>）</p>
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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="kw1">class</span> S <span class="br0">{</span>
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<span class="kw4">int</span> mf1<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 非静态成员函数声明</span>
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<span class="kw4">void</span> mf2<span class="br0">(</span><span class="br0">)</span> <span class="kw4">volatile</span>, mf3<span class="br0">(</span><span class="br0">)</span> <span class="sy3">&&</span><span class="sy4">;</span> <span class="co1">// 可以有 cv 限定或引用限定</span>
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<span class="kw4">int</span> mf4<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <span class="kw1">return</span> data<span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// 可以内联定义</span>
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<span class="kw1">virtual</span> <span class="kw4">void</span> mf5<span class="br0">(</span><span class="br0">)</span> final<span class="sy4">;</span> <span class="co1">// 可以是虚函数，可以使用 final/override</span>
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S<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> data<span class="br0">(</span><span class="nu0">12</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span> <span class="co1">// 构造函数也是成员函数</span>
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<span class="kw4">int</span> data<span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">int</span> S<span class="sy4">::</span><span class="me2">mf1</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">7</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// 不内联定义就必须在命名空间定义</span></pre></div>
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</div>
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<p>允许任何<a href="cpp-language-function.html">函数声明</a>，外加非静态成员函数专用的语法元素：<a href="cpp-language-abstract_class.html">纯说明符</a>，cv 限定符<span class="t-rev-inl t-since-cxx11"><span>，引用限定符，<a href="cpp-language-final.html"><code>final</code></a> 与 <a href="cpp-language-override.html"><code>override</code></a> 说明符</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>，以及<a href="cpp-language-initializer_list.html" class="mw-redirect">成员初始化器列表</a>。</p>
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<p>可以用以下方式调用类 <code>X</code> 的非静态成员函数：</p>
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<div class="t-li1"><span class="t-li">1)</span> 对 <code>X</code> 类型的对象使用类成员访问运算符调用</div>
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<div class="t-li1"><span class="t-li">2)</span> 对<a href="cpp-language-derived_class.html">派生</a>自 <code>X</code> 的类的对象调用</div>
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<div class="t-li1"><span class="t-li">3)</span> 从 <code>X</code> 的成员函数体内直接调用</div>
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<div class="t-li1"><span class="t-li">4)</span> 从派生自 <code>X</code> 的类的成员函数体内调用直接调用</div>
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<p>在类型不是 <code>X</code> 或派生自 <code>X</code> 的对象上调用类 <code>X</code> 的非静态成员函数的行为未定义。</p>
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<p>在 <code>X</code> 的非静态成员函数的体内，任何解析为 <code>X</code> 或 <code>X</code> 的某个基类的非类型非静态成员的<a href="cpp-language-expressions.html">标识表达式</a> <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span>}（例如一个标识符）均被变换为成员访问表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span>.<span class="me1">e</span></span></span>（除非它已经是成员访问表达式的一部分）。模板定义语境中不会发生这种变换，因此有时需要明确地对某个名字前附 <span class="t-c"><span class="mw-geshi cpp source-cpp">this<span class="sy2">-</span><span class="sy1">></span></span></span>，以使其成为<a href="cpp-language-dependent_name.html">待决的</a>名字。</p>
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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="kw1">struct</span> S <span class="br0">{</span>
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<span class="kw4">int</span> n<span class="sy4">;</span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">void</span> S<span class="sy4">::</span><span class="me2">f</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// 变换为 (*this).n = 1;</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> <span class="br0">{</span>
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S s1, s2<span class="sy4">;</span>
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s1.<span class="me1">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 更改 s1.n</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>在 <code>X</code> 的非静态成员函数体内，任何解析到 <code>X</code> 或 <code>X</code> 的某个基类的静态成员、枚举项或嵌套类型的无限定标识均被变换为对应的有限定标识。</p>
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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="kw1">struct</span> S <span class="br0">{</span>
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<span class="kw4">static</span> <span class="kw4">int</span> n<span class="sy4">;</span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">void</span> S<span class="sy4">::</span><span class="me2">f</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// 变换为 S::n = 1;</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> <span class="br0">{</span>
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S s1, s2<span class="sy4">;</span>
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s1.<span class="me1">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 更改 S::n</span>
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<span class="br0">}</span></pre></div>
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</div>
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<h3><span class="mw-headline" id=".E6.9C.89_const_.E4.B8.8E_volatile_.E9.99.90.E5.AE.9A.E7.9A.84.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">有 const 与 volatile 限定的成员函数</span></h3>
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<p>非静态成员函数可以带 const、volatile 或 const volatile 限定符声明（这些限定符出现在<a href="cpp-language-function.html">函数声明</a>中的形参列表之后）。cv 限定性不同的函数具有不同类型，从而可以相互重载。</p>
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<p>在有 cv 限定的函数体内，<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 有同样的 cv 限定，例如在 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span></span></span> 成员函数中只能正常地调用其他 const 成员函数。（如果应用了 <a href="cpp-language-const_cast.html"><code>const_cast</code></a>，或通过不涉及 <a href="cpp-language-this.html"><code>this</code></a> 的访问路径，那么仍然可以调用非 const 成员函数。）</p>
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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 <vector></span>
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<span class="kw1">struct</span> Array <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">int</span><span class="sy1">></span> data<span class="sy4">;</span>
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Array<span class="br0">(</span><span class="kw4">int</span> sz<span class="br0">)</span> <span class="sy4">:</span> data<span class="br0">(</span>sz<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
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<span class="co1">// const 成员函数</span>
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<span class="kw4">int</span> operator<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> idx<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
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<span class="co1">// this 具有类型 const Array*</span>
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<span class="kw1">return</span> data<span class="br0">[</span>idx<span class="br0">]</span><span class="sy4">;</span> <span class="co1">// 变换为 (*this).data[idx];</span>
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<span class="br0">}</span>
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<span class="co1">// 非 const 成员函数</span>
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<span class="kw4">int</span><span class="sy3">&</span> operator<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> idx<span class="br0">)</span> <span class="br0">{</span>
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<span class="co1">// this 具有类型 Array*</span>
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<span class="kw1">return</span> data<span class="br0">[</span>idx<span class="br0">]</span><span class="sy4">;</span> <span class="co1">// 变换为 (*this).data[idx]</span>
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<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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Array a<span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span>
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a<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// OK：a[1] 的类型是 int&</span>
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<span class="kw4">const</span> Array ca<span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span>
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ca<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">2</span><span class="sy4">;</span> <span class="co1">// 错误：ca[1] 的类型是 int</span>
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<span class="br0">}</span></pre></div>
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</div>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx11">
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<td>
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<h3><span class="mw-headline" id=".E6.9C.89.E5.BC.95.E7.94.A8.E9.99.90.E5.AE.9A.E7.9A.84.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">有引用限定的成员函数</span></h3>
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<p>非静态成员函数可以不带引用限定符，带有左值引用限定符（函数名后的 <code>&</code> 记号），或带有右值引用限定符（函数名后的 <code>&&</code> 记号）声明。在<a href="cpp-language-overload_resolution.html">重载决议</a>中，按下列方式对待类 X 的非静态 cv 限定成员函数：</p>
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<ul>
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<li>不带引用限定符：隐式对象形参具有到 cv 限定的 X 的左值引用类型，并额外允许绑定到右值隐含对象实参</li>
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<li>左值引用限定符：隐式对象形参具有到 cv 限定的 X 的左值引用类型</li>
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<li>右值引用限定符：隐式对象形参具有到 cv 限定的 X 的右值引用类型</li>
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</ul>
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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="kw1">struct</span> S <span class="br0">{</span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="sy3">&</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"左值<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="sy3">&&</span><span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"右值<span class="es1">\n</span>"</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><span class="br0">{</span>
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S s<span class="sy4">;</span>
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s.<span class="me1">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 打印“左值”</span>
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std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>s<span class="br0">)</span>.<span class="me1">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 打印“右值”</span>
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S<span class="br0">(</span><span class="br0">)</span>.<span class="me1">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 打印“右值”</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>注意：与 cv 限定性不同，引用限定性不改变 <a href="cpp-language-this.html"><code>this</code></a> 指针的性质：即使在右值引用限定的函数中，<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 仍是左值表达式。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.99.9A.E5.87.BD.E6.95.B0.E5.92.8C.E7.BA.AF.E8.99.9A.E5.87.BD.E6.95.B0">虚函数和纯虚函数</span></h3>
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<p>非静态成员函数可以声明为<i>虚</i>或<i>纯虚</i>函数。细节见<a href="cpp-language-virtual.html">虚函数</a>与<a href="cpp-language-abstract_class.html">抽象类</a>。</p>
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<h3><span class="mw-headline" id=".E7.89.B9.E6.AE.8A.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">特殊成员函数</span></h3>
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<p><a href="cpp-language-constructor.html">构造函数</a>和<a href="cpp-language-destructor.html">析构函数</a>是非静态成员函数，在其声明中使用特殊的语法（细节见其相应页面）。</p>
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<p>一些成员函数是<i>特殊</i>的：在某些环境下，即使用户不定义编译器也会定义它们。它们是：</p>
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<ul>
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<li><a href="cpp-language-default_constructor.html">默认构造函数</a></li>
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<li><a href="cpp-language-copy_constructor.html">复制构造函数</a></li>
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</ul>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx11">
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<td>
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<ul>
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<li><a href="cpp-language-move_constructor.html">移动构造函数</a></li>
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</ul>
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</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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</table>
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<ul>
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<li><a href="cpp-language-copy_assignment.html">复制赋值运算符</a></li>
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</ul>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx11">
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<td>
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<ul>
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<li><a href="cpp-language-move_assignment.html">移动赋值运算符</a></li>
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</ul>
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</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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</table>
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<ul>
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<li>
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<table class="t-rev-begin">
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<tr class="t-rev t-until-cxx20">
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<td>
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<p><a href="cpp-language-destructor.html">析构函数</a></p>
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</td>
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<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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<tr class="t-rev t-since-cxx20">
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<td>
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<p><a href="cpp-language-destructor.html#.E9.A2.84.E6.9C.9F.E7.9A.84.E6.9E.90.E6.9E.84.E5.87.BD.E6.95.B0">预期的析构函数</a></p>
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</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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</table>
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<p>特殊成员函数<span class="t-rev-inl t-since-cxx20"><span>以及<a href="cpp-language-default_comparisons.html">比较运算符</a></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>是仅有的能被<i>预置</i>的函数，即使用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">=</span> <span class="kw1">default</span></span></span> 替代函数体进行定义（细节见其相应页面）。</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 <string></span>
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<span class="co2">#include <utility></span>
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<span class="co2">#include <exception></span>
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<span class="kw1">struct</span> S <span class="br0">{</span>
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<span class="kw4">int</span> data<span class="sy4">;</span>
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<span class="co1">// 简单的转换构造函数（声明）</span>
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S<span class="br0">(</span><span class="kw4">int</span> val<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 简单的显式构造函数（声明）</span>
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<span class="kw1">explicit</span> S<span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> str<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// const 成员函数（定义）</span>
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<span class="kw1">virtual</span> <span class="kw4">int</span> getData<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <span class="kw1">return</span> data<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="co1">// 构造函数的定义</span>
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S<span class="sy4">::</span><span class="me2">S</span><span class="br0">(</span><span class="kw4">int</span> val<span class="br0">)</span> <span class="sy4">:</span> data<span class="br0">(</span>val<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> <span class="st0">"调用构造函数1，data = "</span> <span class="sy1"><<</span> data <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="co1">// 此构造函数拥有 catch 子句</span>
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S<span class="sy4">::</span><span class="me2">S</span><span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> str<span class="br0">)</span> <span class="kw1">try</span> <span class="sy4">:</span> data<span class="br0">(</span><a href="cpp-string-basic_string-stol.html"><span class="kw1257">std::<span class="me2">stoi</span></span></a><span class="br0">(</span>str<span class="br0">)</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> <span class="st0">"调用构造函数2，data = "</span> <span class="sy1"><<</span> data <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> <span class="kw1">catch</span><span class="br0">(</span><span class="kw4">const</span> <a href="cpp-error-exception.html"><span class="kw764">std::<span class="me2">exception</span></span></a><span class="sy3">&</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> <span class="st0">"构造函数2失败，字符串'"</span> <span class="sy1"><<</span> str <span class="sy1"><<</span> <span class="st0">"'<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">throw</span><span class="sy4">;</span> <span class="co1">// 构造函数的 catch 子句应该始终再抛出异常</span>
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<span class="br0">}</span>
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<span class="kw1">struct</span> D <span class="sy4">:</span> S <span class="br0">{</span>
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<span class="kw4">int</span> data2<span class="sy4">;</span>
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<span class="co1">// 带默认实参的构造函数</span>
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D<span class="br0">(</span><span class="kw4">int</span> v1, <span class="kw4">int</span> v2 <span class="sy1">=</span> <span class="nu0">11</span><span class="br0">)</span> <span class="sy4">:</span> S<span class="br0">(</span>v1<span class="br0">)</span>, data2<span class="br0">(</span>v2<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
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<span class="co1">// 虚成员函数</span>
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<span class="kw4">int</span> getData<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> override <span class="br0">{</span> <span class="kw1">return</span> data<span class="sy2">*</span>data2<span class="sy4">;</span> <span class="br0">}</span>
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<span class="co1">// 左值限定的赋值运算符</span>
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D<span class="sy3">&</span> operator<span class="sy1">=</span><span class="br0">(</span>D other<span class="br0">)</span> <span class="sy3">&</span> <span class="br0">{</span>
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<a href="cpp-algorithm-swap.html"><span class="kw1599">std::<span class="me2">swap</span></span></a><span class="br0">(</span>other.<span class="me1">data</span>, data<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-algorithm-swap.html"><span class="kw1599">std::<span class="me2">swap</span></span></a><span class="br0">(</span>other.<span class="me1">data2</span>, data2<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <span class="sy2">*</span>this<span class="sy4">;</span>
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<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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D d1 <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
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S s2<span class="br0">(</span><span class="st0">"2"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">try</span> <span class="br0">{</span>
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S s3<span class="br0">(</span><span class="st0">"不是数字"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">catch</span><span class="br0">(</span><span class="kw4">const</span> <a href="cpp-error-exception.html"><span class="kw764">std::<span class="me2">exception</span></span></a><span class="sy3">&</span><span class="br0">)</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> s2.<span class="me1">getData</span><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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D d2<span class="br0">(</span><span class="nu0">3</span>, <span class="nu0">4</span><span class="br0">)</span><span class="sy4">;</span>
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d2 <span class="sy1">=</span> d1<span class="sy4">;</span> <span class="co1">// OK ：赋值给左值</span>
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<span class="co1">// D(5) = d1; // 错误：没有适合的 operator= 重载</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">调用构造函数1，data = 1
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调用构造函数2，data = 2
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构造函数2失败，字符串'不是数字'
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2
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调用构造函数1，data = 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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<ul>
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<li><a href="cpp-language-classes.html">类</a></li>
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<li><a href="cpp-language-data_members.html">数据成员</a></li>
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<li><a href="cpp-language-static.html">静态数据成员</a></li>
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</ul>
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</li>
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</ul>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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