740 lines
71 KiB
HTML
740 lines
71 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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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>其他运算符</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_language_operator_other 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">其他运算符</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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<table class="wikitable" style="font-size:85%;">
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<tr>
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<th rowspan="2">运算符名</th>
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<th rowspan="2">语法</th>
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<th rowspan="2"><a href="cpp-language-operators.html">可重载</a></th>
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<th colspan="2">原型示例（对于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> T</span></span>）</th>
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</tr>
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<tr>
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<th>类内定义</th>
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<th>类外定义</th>
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</tr>
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<tr>
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<td>函数调用</td>
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<td><code>a(a1, a2)</code></td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">R T<span class="sy4">::</span><span class="me2">operator</span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>Arg1 <span class="sy3">&</span>a1, Arg2 <span class="sy3">&</span>a2, ... ...<span class="br0">)</span><span class="sy4">;</span></span></span></td>
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<td style="background: #ececec; color: grey; vertical-align: middle; text-align: center;" class="table-na"><small>N/A</small></td>
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</tr>
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<tr>
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<td>逗号</td>
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<td><code>a, b</code></td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">T2<span class="sy3">&</span> T<span class="sy4">::</span><span class="me2">operator</span>,<span class="br0">(</span>T2 <span class="sy3">&</span>b<span class="br0">)</span><span class="sy4">;</span></span></span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">T2<span class="sy3">&</span> operator,<span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&</span>a, T2 <span class="sy3">&</span>b<span class="br0">)</span><span class="sy4">;</span></span></span></td>
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</tr>
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<tr>
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<td>条件</td>
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<td><code>a ? b : c</code></td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">否</td>
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<td style="background: #ececec; color: grey; vertical-align: middle; text-align: center;" class="table-na"><small>N/A</small></td>
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<td style="background: #ececec; color: grey; vertical-align: middle; text-align: center;" class="table-na"><small>N/A</small></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
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<p><i>函数调用</i>运算符为任何对象提供函数语义。</p>
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<p><i>条件</i>运算符（通俗地称为“三元条件”）检查第一表达式的布尔值，然后根据其结果值，求值并返回第二或第三表达式。</p>
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<h4><span class="mw-headline" id=".E5.86.85.E5.BB.BA.E7.9A.84.E5.87.BD.E6.95.B0.E8.B0.83.E7.94.A8.E8.BF.90.E7.AE.97.E7.AC.A6">内建的函数调用运算符</span></h4>
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<p>函数调用表达式的形式为</p>
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<table class="t-sdsc-begin">
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td class="t-sdsc-nopad"><span class="t-spar">函数表达式</span> <code><b>(</b></code> <span class="t-spar">实参1, 实参2, 实参3,...</span> <code><b>)</b></code></td>
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<td class="t-sdsc-nopad"></td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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</table>
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<p>其中</p>
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<ul>
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<li><span class="t-spar">函数表达式</span> 是指名<a href="cpp-language-functions.html">函数</a>的表达式</li>
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<li><span class="t-spar">实参1, 实参2, 实参3,...</span> 是可能为空的任意表达式的列表，但为避免歧义不允许顶层出现逗号运算符。</li>
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</ul>
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<p>指名函数的表达式可以为</p>
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<div class="t-li1"><span class="t-li">a)</span> 指代函数的左值表达式</div>
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<div class="t-li1"><span class="t-li">b)</span> 函数指针</div>
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<div class="t-li1"><span class="t-li">c)</span> 选择成员函数的显式<a href="cpp-language-operator_member_access.html">类成员访问</a>表达式</div>
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<div class="t-li1"><span class="t-li">d)</span> 隐式类成员访问表达式，例如在另一成员函数内使用的成员函数名。</div>
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<p>由<span class="t-spar">函数表达式</span> 所指代的函数（或成员）名可以是重载的，用<a href="cpp-language-overload_resolution.html">重载决议</a>规则决定要调用哪个重载。</p>
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<p>若<span class="t-spar">函数表达式</span> 指定成员函数，则它可为虚，这种情况下将以运行时的动态派发调用该函数的最终覆盖函数。</p>
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<p>为调用该函数，</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-until-cxx17">
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<td>
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<p>以任意顺序对表达式<span class="t-spar">函数表达式</span> 和作为实参所提供的所有表达式<span class="t-spar">实参1</span>、<span class="t-spar">实参2</span>、<span class="t-spar">实参3</span> 等进行求值，它们互相是<a href="cpp-language-eval_order.html">无顺序的（unsequenced）</a>。</p>
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</td>
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<td><span class="t-mark-rev t-until-cxx17">(C++17 前)</span></td>
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</tr>
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<tr class="t-rev t-since-cxx17">
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<td>
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<p>表达式<span class="t-spar">函数表达式</span> 按顺序早于（sequenced before）表达式 <span class="t-spar">实参1</span>、<span class="t-spar">实参2</span>、<span class="t-spar">实参3</span> 以及各默认实参（若存在）。以任意顺序求值各实参表达式，它们互相是<a href="cpp-language-eval_order.html">顺序不确定的（indeterminately sequenced）</a>。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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</table>
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<p>各个函数形参以其对应实参（若需要，经过<a href="cpp-language-implicit_conversion.html">隐式转换</a>后）初始化。若没有对应实参，则使用对应的<a href="cpp-language-default_arguments.html">默认实参</a>，而若其不存在则程序非良构。如果所进行的是成员函数调用，则将指向当前对象的 <span class="t-c"><span class="mw-geshi cpp source-cpp">this</span></span> 指针，如同使用显式转型一般，转换到函数所期待的 <span class="t-c"><span class="mw-geshi cpp source-cpp">this</span></span> 指针。各个形参的初始化和销毁是在调用方的语境中进行的，这意味着，例如当某个形参的构造函数抛出异常时，不会考虑定义于函数内的异常处理块，即使是函数 try 块也如此。若函数为变参函数，则对省略号形参所匹配的所有实参实施<a href="cpp-language-variadic_arguments.html#.E9.BB.98.E8.AE.A4.E8.BD.AC.E6.8D.A2">默认实参提升</a>。形参的<a href="cpp-language-lifetime.html">生存期</a>是结束于定义它的函数返回时，还是外围全表达式的结尾，是由实现定义的。</p>
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<p>函数调用表达式的返回类型是被选择函数的返回类型，以静态绑定决定（忽略 <code>virtual</code> 关键词），即使实际调用的覆盖函数返回不同的类型。这允许覆盖函数返回引用或指针，指向派生于基类函数所返回类型的类，即 C++ 支持<a href="https://en.wikipedia.org/wiki/Covariant_return_type" class="extiw" title="enwiki:Covariant return type">协变（covariant）返回类型</a>。若 <code>E</code> 指定析构函数，则返回类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx17">
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<td>
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<p>当一个类类型 X 的对象被传递给函数，或被从函数返回时，如果 X 的每个复制构造函数、移动构造函数和析构函数均为平凡或被弃置（delete）的，并且 X 拥有至少一个未被弃置的复制或移动构造函数，则容许实现创建保有函数形参或结果对象的临时对象。</p>
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<p>临时对象分别从函数实参或返回值构造，而函数的形参或返回对象的初始化，如同使用未被弃置的平凡构造函数对临时对象进行复制一样进行（即使该构造函数无法访问，或它并不会被进行对象的复制或移动时的重载决议所选择，也是如此）。</p>
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<p>这允许小的类类型（如 <span class="t-lc"><a href="cpp-numeric-complex.html">std::complex</a></span> 或 <code>std::span</code>）可以在寄存器中传递给函数或从函数返回。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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</table>
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<p>若函数返回左值引用或到函数的右值引用，则函数调用表达式的值类别为左值，若函数返回到对象的右值引用，则值类别为亡值，否则值类别为纯右值。若函数调用表达式为对象类型的纯右值，则它必须拥有完整对象类型，除非<span class="t-rev-inl t-since-cxx17"><span>该纯右值不会被实质化，比如</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span>用作 <a href="cpp-language-decltype.html">decltype</a> 的操作数，或用作作为 <code>decltype</code> 操作数的<a href="cpp-language-operator_other.html#.E5.86.85.E5.BB.BA.E7.9A.84.E9.80.97.E5.8F.B7.E8.BF.90.E7.AE.97.E7.AC.A6">内建逗号运算符表达式</a>的右操作数。</p>
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<p>函数调用表达式在语法上与值初始化 <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="br0">(</span><span class="br0">)</span></span></span>，<a href="cpp-language-explicit_cast.html">函数风格转型</a>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="br0">(</span>A1<span class="br0">)</span></span></span>，以及临时量的直接初始化 <span class="t-c"><span class="mw-geshi cpp source-cpp">T<span class="br0">(</span>A1, A2, A3, ...<span class="br0">)</span></span></span> 相似，其中 <code>T</code> 是一个类型的名称。</p>
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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 <cstdio></span>
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<span class="kw1">struct</span> S
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<span class="br0">{</span>
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<span class="kw4">int</span> f1<span class="br0">(</span><span class="kw4">double</span> d<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> printf<span class="br0">(</span><span class="st0">"%f <span class="es1">\n</span>"</span>, d<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 变参函数调用</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> f2<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</span> f1<span class="br0">(</span><span class="nu0">7</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 成员函数调用，同 this->f1()</span>
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<span class="co1">// 整数形参转换为 double</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">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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puts<span class="br0">(</span><span class="st0">"函数已调用"</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 函数调用</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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f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 函数调用</span>
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S s<span class="sy4">;</span>
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s.<span class="me1">f2</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 成员函数调用</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">函数已调用
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7.000000</pre></div>
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</div>
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</div>
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<h4><span class="mw-headline" id=".E5.86.85.E5.BB.BA.E7.9A.84.E9.80.97.E5.8F.B7.E8.BF.90.E7.AE.97.E7.AC.A6">内建的逗号运算符</span></h4>
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<p>逗号运算符表达式的形式为</p>
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<table class="t-sdsc-begin">
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td class="t-sdsc-nopad"><span class="t-spar">表达式1</span> <code><b>,</b></code> <span class="t-spar">表达式2</span></td>
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<td class="t-sdsc-nopad"></td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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</table>
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<p>逗号表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1, E2</span></span> 中，对 <code>E1</code> 求值并<a href="cpp-language-expressions.html#.E5.BC.83.E5.80.BC.E8.A1.A8.E8.BE.BE.E5.BC.8F">舍弃</a>其结果（尽管当它具有类类型时，直到<a href="cpp-language-lifetime.html#.E4.B8.B4.E6.97.B6.E5.AF.B9.E8.B1.A1.E7.9A.84.E7.94.9F.E5.AD.98.E6.9C.9F">包含它的全表达式的结尾</a>之前都不会销毁它），其副作用在表达式 <code>E2</code> 的求值开始前完成<span class="t-rev-inl t-until-cxx17"><span>（注意，用户定义的 <code>operator,</code> 不能保证定序）</span> <span><span class="t-mark-rev t-until-cxx17">(C++17 前)</span></span></span>。</p>
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<p>逗号表达式结果的类型、值和值类别严格为其第二操作数 <code>E2</code> 的类型、值和值类别。若 <code>E2</code> 为临时量<span class="t-rev-inl t-since-cxx17"><span>表达式</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span>，则表达式的结果为该临时量<span class="t-rev-inl t-since-cxx17"><span>表达式</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span>。若 <code>E2</code> 为位域，则结果为位域。</p>
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<p>各种逗号分隔列表，例如函数实参列表（<span class="t-c"><span class="mw-geshi cpp source-cpp">f<span class="br0">(</span>a, b, c<span class="br0">)</span></span></span>）和初始化器列表 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> a<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span><span class="br0">}</span></span></span>，其中的逗号都不是逗号运算符。若需要在这种语境中使用逗号运算符，则必须加括号：<span class="t-c"><span class="mw-geshi cpp source-cpp">f<span class="br0">(</span>a, <span class="br0">(</span>n<span class="sy2">++</span>, n<span class="sy2">+</span>b<span class="br0">)</span>, c<span class="br0">)</span></span></span>。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx20 t-until-cxx23">
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<td>
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<p>以无括号的逗号表达式为<a href="cpp-language-operator_member_access.html#.E5.86.85.E5.BB.BA.E7.9A.84.E4.B8.8B.E6.A0.87.E8.BF.90.E7.AE.97.E7.AC.A6">下标运算符</a>的第二（右）操作数是被弃用的。</p>
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<p>例如， <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>b, c<span class="br0">]</span></span></span> 被弃用而 <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span><span class="br0">(</span>b, c<span class="br0">)</span><span class="br0">]</span></span></span> 未被弃用。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span><br />
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<span class="t-mark-rev t-until-cxx23">(C++23 前)</span></td>
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</tr>
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<tr class="t-rev t-since-cxx23">
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<td>
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<p>无括号的逗号表达式不能为<a href="cpp-language-operator_member_access.html#.E5.86.85.E5.BB.BA.E7.9A.84.E4.B8.8B.E6.A0.87.E8.BF.90.E7.AE.97.E7.AC.A6">下标运算符</a>的第二（右）参数。例如 <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>b, c<span class="br0">]</span></span></span> 要么非良构要么等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="me1">operator</span><span class="br0">[</span><span class="br0">]</span><span class="br0">(</span>b, c<span class="br0">)</span></span></span>。</p>
|
|
<p>为将逗号表达式用作下标需要括号，例如 <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span><span class="br0">(</span>b, c<span class="br0">)</span><span class="br0">]</span></span></span>。</p>
|
|
</td>
|
|
<td><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></td>
|
|
</tr>
|
|
</table>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <iostream></span>
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
|
|
<span class="kw4">int</span> m <span class="sy1">=</span> <span class="br0">(</span><span class="sy2">++</span>n, <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"n = "</span> <span class="sy1"><<</span> n <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>, <span class="sy2">++</span>n, <span class="nu0">2</span><span class="sy2">*</span>n<span class="br0">)</span><span class="sy4">;</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">"m = "</span> <span class="sy1"><<</span> <span class="br0">(</span><span class="sy2">++</span>m, m<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">n = 2
|
|
m = 7</pre></div>
|
|
</div>
|
|
</div>
|
|
<h4><span class="mw-headline" id=".E6.9D.A1.E4.BB.B6.E8.BF.90.E7.AE.97.E7.AC.A6">条件运算符</span></h4>
|
|
<p>条件运算符表达式的形式为</p>
|
|
<table class="t-sdsc-begin">
|
|
<tr>
|
|
<td colspan="10" class="t-sdsc-sep"></td>
|
|
</tr>
|
|
<tr class="t-sdsc">
|
|
<td class="t-sdsc-nopad"><span class="t-spar">表达式1</span> <code><b>?</b></code> <span class="t-spar">表达式2</span> <code><b>:</b></code> <span class="t-spar">表达式3</span></td>
|
|
<td class="t-sdsc-nopad"></td>
|
|
<td class="t-sdsc-nopad"></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="10" class="t-sdsc-sep"></td>
|
|
</tr>
|
|
</table>
|
|
<p>对条件运算符的第一操作数求值并将其<a href="cpp-language-implicit_conversion.html">按语境转换</a>为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span>。当第一操作数的值计算和所有副作用完成之后，若结果为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span>，则求值第二操作数。若结果为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span>，则求值第三操作数。</p>
|
|
<p>条件表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">E1 <span class="sy4">?</span> E2 <span class="sy4">:</span> E3</span></span> 的类型和值类别按照下列规则确定：</p>
|
|
<div class="t-li1"><span class="t-li">1)</span> 若 <code>E2</code> 或 <code>E3</code> 具有 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 类型，则下列之一必须为真，否则程序非良构：</div>
|
|
<div class="t-li2"><span class="t-li">1.1)</span> <code>E2</code> 或 <code>E3</code>（但非两者）为（可带括号的）<a href="cpp-language-throw.html">throw 表达式</a>。条件运算符的结果具有另一表达式的类型和值类别。若另一表达式为<a href="cpp-language-bit_field.html">位域</a>，则结果为位域。这种条件运算符常用于 C++14 之前的 C++11 <a href="cpp-language-constexpr.html">constexpr 编程</a>。
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> str <span class="sy1">=</span> <span class="nu0">2</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy1">==</span><span class="nu0">4</span> <span class="sy4">?</span> <span class="st0">"ok"</span> <span class="sy4">:</span> <span class="kw1">throw</span> <a href="cpp-error-logic_error.html"><span class="kw765">std::<span class="me2">logic_error</span></span></a><span class="br0">(</span><span class="st0">"2+2 != 4"</span><span class="br0">)</span><span class="sy4">;</span></pre></div>
|
|
</div>
|
|
</div>
|
|
<div class="t-li2"><span class="t-li">1.2)</span> <code>E2</code> 和 <code>E3</code> 都具有 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 类型（包括两者均为 throw 表达式的情况）。结果为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 类型的纯右值。
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="nu0">2</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy1">==</span><span class="nu0">4</span> <span class="sy4">?</span> <span class="kw1">throw</span> <span class="nu0">123</span> <span class="sy4">:</span> <span class="kw1">throw</span> <span class="nu0">456</span><span class="sy4">;</span></pre></div>
|
|
</div>
|
|
</div>
|
|
<table class="t-rev-begin">
|
|
<tr class="t-rev t-since-cxx14">
|
|
<td>
|
|
<div class="t-li1"><span class="t-li">2)</span> 否则，若 <code>E2</code> 或 <code>E3</code> 均为值类别相同的泛左值位域，类型分别为 cv1 T 和 cv2 T，则此节剩下的部分中认为这些操作数都拥有 cv T 类型，其中 cv 是 cv1 与 cv2 的合并。</div>
|
|
</td>
|
|
<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
|
|
</tr>
|
|
</table>
|
|
<div class="t-li1"><span class="t-li">3)</span> 否则，若 <code>E2</code> 与 <code>E3</code> 拥有不同类型且至少有一个是（可有 cv 限定的）类类型，或都是同一值类别的泛左值且具有除了 cv 限定性之外都相同的类型，则尝试组成<a href="cpp-language-implicit_conversion.html">隐式转换序列</a><span class="t-rev-inl t-since-cxx14"><span>（其中忽略成员访问，操作数是否为位域，或转换函数是否被弃置）</span> <span><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></span></span>，从每个操作数转换到由另一操作数所确定的<i>目标类型</i>，如下文所述。一个名为 <code>X</code> 的 <code>TX</code> 类型的操作数，能以如下方式转换成另一名为 <code>Y</code> 的 <code>TY</code> 类型操作数的<i>目标类型</i>：</div>
|
|
<div class="t-li2"><span class="t-li">3.1)</span> 若 <code>Y</code> 为左值，则目标类型为 <code>TY&</code>，且引用必须直接绑定到左值；</div>
|
|
<div class="t-li2"><span class="t-li">3.2)</span> 若 <code>Y</code> 为亡值，则目标类型为 <code>TY&&</code>，且引用必须直接绑定；</div>
|
|
<div class="t-li2"><span class="t-li">3.3)</span> 若 <code>Y</code> 为纯右值，或若两个转换序列都无法组成，且 <code>TX</code> 和 <code>TY</code> 至少有一个是（可为 cv 限定的）类类型，</div>
|
|
<div class="t-li3"><span class="t-li">3.3.1)</span> 若 <code>TX</code> 和 <code>TY</code>（忽略 cv 限定性）为相同类类型，且 <code>TY</code> 至少有 <code>TX</code> 的 cv 限定，则目标类型为 <code>TY</code>,</div>
|
|
<div class="t-li3"><span class="t-li">3.3.2)</span> 否则，若 <code>TY</code> 是 <code>TX</code> 的基类，则目标类型为带有 <code>TX</code> 的 cv 限定符的 <code>TY</code>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="kw1">struct</span> A <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="kw1">struct</span> B <span class="sy4">:</span> A <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="kw1">using</span> T <span class="sy1">=</span> <span class="kw4">const</span> B<span class="sy4">;</span>
|
|
A a <span class="sy1">=</span> <span class="kw2">true</span> <span class="sy4">?</span> A<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> T<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// Y = A(), TY = A, X = T(), TX = const B. 目标类型 = const A</span></pre></div>
|
|
</div>
|
|
</div>
|
|
<div class="t-li3"><span class="t-li">3.3.3)</span> 否则，目标类型为 <code>Y</code> 在应用左值到右值、数组到指针和函数到指针<a href="cpp-language-implicit_conversion.html">标准转换</a>后会有的类型。</div>
|
|
<div class="t-li2"><span class="t-li">3.4)</span> 若两个序列（E2 到 E3 的目标类型和 E3 到 E2 的目标类型）均可组成，或只能组成一个但它是有歧义转换序列，则程序非良构。</div>
|
|
<div class="t-li2"><span class="t-li">3.5)</span> 若恰能组成一个转换序列（注意它仍然可能非良构，例如由于访问违规），则应用该转换序列，此描述的余下部分（从 <span class="t-v">(4)</span> 之后）中用转换后的操作数取代原操作数。</div>
|
|
<div class="t-li2"><span class="t-li">3.6)</span> 若不能组成任何转换序列，则在此描述的余下部分中保留各操作数不变。</div>
|
|
<div class="t-li1"><span class="t-li">4)</span> 若 <code>E2</code> 与 <code>E3</code> 是同类型和同值类别的泛左值，则结果具有相同的类型和值类别，而若 <code>E2</code> 与 <code>E3</code> 至少有一个是位域，则结果为位域。</div>
|
|
<div class="t-li1"><span class="t-li">5)</span> 否则，结果为纯右值。若 <code>E2</code> 与 <code>E3</code> 具有不同类型，且一者拥有（可为 cv 限定的）类类型，则尝试用下文的各内建候选函数将操作数转换为内建类型，并为此实施重载决议。若重载决议失败，则程序非良构。否则，应用所选择的转换，并在步骤 6 用转换后的操作数取代原操作数。</div>
|
|
<div class="t-li1"><span class="t-li">6)</span> 对第二和第三操作数应用左值到右值、数组到指针和函数到指针转换，然后，</div>
|
|
<div class="t-li2"><span class="t-li">6.1)</span> 若 <code>E2</code> 与 <code>E3</code> 现在均具有相同类型，则结果是该类型的纯右值，<span class="t-rev-inl t-until-cxx17"><span>指代一个临时对象，</span> <span><span class="t-mark-rev t-until-cxx17">(C++17 前)</span></span></span><span class="t-rev-inl t-since-cxx17"><span>其结果对象</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span>从求值 <code>E1</code> 后选择的那个操作数进行复制初始化。</div>
|
|
<div class="t-li2"><span class="t-li">6.2)</span> 若 <code>E2</code> 与 <code>E3</code> 均具有算术或枚举类型：则应用<a href="cpp-language-operator_arithmetic.html#.E8.BD.AC.E6.8D.A2"><i>一般算术转换</i></a>将它们变为<i>公共类型</i>，而该类型即是结果。</div>
|
|
<div class="t-li2"><span class="t-li">6.3)</span> 若 <code>E2</code> 与 <code>E3</code> 均为指针，或一个是指针而另一个是空指针常量，则应用指针转换和限定性转换，将它们变为公共类型，而该类型即是结果。</div>
|
|
<div class="t-li2"><span class="t-li">6.4)</span> 若 <code>E2</code> 与 <code>E3</code> 均为成员指针，或一个是成员指针而另一个是空指针常量，则应用成员指针转换和限定性转换，将它们变成公共类型，而该类型即是结果。</div>
|
|
<div class="t-li2"><span class="t-li">6.5)</span> 若 <code>E2</code> 与 <code>E3</code> 均为空指针常量，而至少有一个为 <span class="t-lc"><a href="cpp-types-nullptr_t.html">std::nullptr_t</a></span> 类型，则结果类型为 <code>std::nullptr_t</code>。</div>
|
|
<div class="t-li2"><span class="t-li">6.6)</span> 所有其他情况下，程序非良构。</div>
|
|
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
|
|
<tr>
|
|
<td class="mbox-empty-cell"></td>
|
|
<td class="mbox-text" style="">本节未完成<br />
|
|
原因：任何令此更可读，而不遗漏重点的机会？退一步来说，给每条一个一行的小示例会大有裨益</td>
|
|
</tr>
|
|
</table>
|
|
<p>对于每对提升后的算术类型 L 和 R 并对于每个类型 P，其中 P 为指针、成员指针或有作用域枚举类型，下列函数签名在上述规则的步骤 5 参与重载决议：</p>
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dcl">
|
|
<td class="t-dcl-nopad">
|
|
<div><span class="mw-geshi cpp source-cpp">LR operator<span class="sy4">?:</span><span class="br0">(</span><span class="kw4">bool</span>, L, R <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td class="t-dcl-nopad">
|
|
<div><span class="mw-geshi cpp source-cpp">P operator<span class="sy4">?:</span><span class="br0">(</span><span class="kw4">bool</span>, P, P <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>其中 LR 是 <code>L</code> 和 <code>R</code> 上进行的<a href="cpp-language-operator_arithmetic.html">一般算术转换</a>的结果。不能重载运算符 “?:”，这些函数签名只为重载决议的目的存在。</p>
|
|
<p>条件运算符的返回类型亦能作为二元类型特性 <span class="t-lc"><a href="cpp-types-common_type.html">std::common_type</a></span> 访问。</p>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <string></span>
|
|
<span class="co2">#include <iostream></span>
|
|
<span class="kw1">struct</span> Node
|
|
<span class="br0">{</span>
|
|
Node<span class="sy2">*</span> next<span class="sy4">;</span>
|
|
<span class="kw4">int</span> data<span class="sy4">;</span>
|
|
<span class="co1">// 深复制的复制构造函数</span>
|
|
Node<span class="br0">(</span><span class="kw4">const</span> Node<span class="sy3">&</span> other<span class="br0">)</span>
|
|
<span class="sy4">:</span> next<span class="br0">(</span>other.<span class="me1">next</span> <span class="sy4">?</span> new Node<span class="br0">(</span><span class="sy2">*</span>other.<span class="me1">next</span><span class="br0">)</span> <span class="sy4">:</span> <a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span>
|
|
, data<span class="br0">(</span>other.<span class="me1">data</span><span class="br0">)</span>
|
|
<span class="br0">{</span><span class="br0">}</span>
|
|
Node<span class="br0">(</span><span class="kw4">int</span> d<span class="br0">)</span> <span class="sy4">:</span> next<span class="br0">(</span><a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span>, data<span class="br0">(</span>d<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
|
|
~Node<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> delete next <span class="sy4">;</span> <span class="br0">}</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="co1">// 简单的右值示例</span>
|
|
<span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span> <span class="sy1">></span> <span class="nu0">2</span> <span class="sy4">?</span> <span class="nu0">10</span> <span class="sy4">:</span> <span class="nu0">11</span><span class="sy4">;</span> <span class="co1">// 1 > 2 为 false，故 n = 11</span>
|
|
<span class="co1">// 简单的左值示例</span>
|
|
<span class="kw4">int</span> m <span class="sy1">=</span> <span class="nu0">10</span><span class="sy4">;</span>
|
|
<span class="br0">(</span>n <span class="sy1">==</span> m <span class="sy4">?</span> n <span class="sy4">:</span> m<span class="br0">)</span> <span class="sy1">=</span> <span class="nu0">7</span><span class="sy4">;</span> <span class="co1">// n == m 为 false，故 m = 7</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">"n = "</span> <span class="sy1"><<</span> n <span class="sy1"><<</span> <span class="st0">"<span class="es1">\n</span>m = "</span> <span class="sy1"><<</span> m<span class="sy4">;</span> <span class="co1">// 输出结果</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">n = 11
|
|
m = 7</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E6.A0.87.E5.87.86.E5.BA.93">标准库</span></h3>
|
|
<p>标准库中许多类都重载了 <code>operator()</code>，以使其能被用作函数对象。</p>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-memory-default_delete.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>删除对象或数组<br />
|
|
<span class="t-mark">(<code>std::default_delete<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-plus.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回两个实参的和<br />
|
|
<span class="t-mark">(<code>std::plus<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-minus.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回两个实参的差<br />
|
|
<span class="t-mark">(<code>std::minus<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-multiplies.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回两个实参的乘积<br />
|
|
<span class="t-mark">(<code>std::multiplies<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-divides.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回第一个实参除以第二个实参的结果<br />
|
|
<span class="t-mark">(<code>std::divides<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-modulus.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回第一个实参除以第二个实参的余数<br />
|
|
<span class="t-mark">(<code>std::modulus<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-negate.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回其实参的非<br />
|
|
<span class="t-mark">(<code>std::negate<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-equal_to.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>检查实参是否相等<br />
|
|
<span class="t-mark">(<code>std::equal_to<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-not_equal_to.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>检查实参是否不相等<br />
|
|
<span class="t-mark">(<code>std::not_equal_to<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-greater.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>检查第一个实参是否大于第二个实参<br />
|
|
<span class="t-mark">(<code>std::greater<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-less.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>检查第一个实参是否小于第二个实参<br />
|
|
<span class="t-mark">(<code>std::less<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-greater_equal.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>检查第一个实参是否大于或等于第二个实参<br />
|
|
<span class="t-mark">(<code>std::greater_equal<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-less_equal.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>检查第一个实参是否小于或等于第二个实参<br />
|
|
<span class="t-mark">(<code>std::less_equal<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-logical_and.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回两个实参的逻辑 AND<br />
|
|
<span class="t-mark">(<code>std::logical_and<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-logical_or.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回两个实参的逻辑 OR<br />
|
|
<span class="t-mark">(<code>std::logical_or<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-logical_not.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回其实参的逻辑 NOT<br />
|
|
<span class="t-mark">(<code>std::logical_not<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-bit_and.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回两个实参的按位 AND 的结果<br />
|
|
<span class="t-mark">(<code>std::bit_and<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-bit_or.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回两个实参的按位 OR 的结果<br />
|
|
<span class="t-mark">(<code>std::bit_or<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-bit_xor.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回两个实参的按位 XOR 的结果<br />
|
|
<span class="t-mark">(<code>std::bit_xor<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-unary_negate.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回对其所存储的谓词调用的结果的逻辑补<br />
|
|
<span class="t-mark">(<code>std::unary_negate<Predicate></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-binary_negate.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>返回对其所存储的谓词的调用的结果的逻辑补<br />
|
|
<span class="t-mark">(<code>std::binary_negate<Predicate></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-reference_wrapper-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>调用其所存储的函数<br />
|
|
<span class="t-mark">(<code>std::reference_wrapper<T></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-utility-functional-function-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>调用其目标<br />
|
|
<span class="t-mark">(<code>std::function<R(Args...)></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-locale-locale-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>用此 locale 的 collate 刻面以字典序比较两个字符串<br />
|
|
<span class="t-mark">(<code>std::locale</code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-map-value_compare.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>比较两个 <code>value_type</code> 类型的值<br />
|
|
<span class="t-mark">(<code>std::map<Key,T,Compare,Allocator>::value_compare</code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-multimap-value_compare.html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>比较两个 <code>value_type</code> 类型的值<br />
|
|
<span class="t-mark">(<code>std::multimap<Key,T,Compare,Allocator>::value_compare</code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-thread-packaged_task-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>执行函数<br />
|
|
<span class="t-mark">(<code>std::packaged_task<R(Args...)></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-numeric-random-linear_congruential_engine-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>推进引擎状态并返回生成的值<br />
|
|
<span class="t-mark">(<code>std::linear_congruential_engine<UIntType,a,c,m></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-numeric-random-uniform_int_distribution-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>生成分布中的下个随机数<br />
|
|
<span class="t-mark">(<code>std::uniform_int_distribution<IntType></code> 的公开成员函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
<p>标准库中的任何类都不重载逗号运算符。boost 库将 <code>operator,</code> 用于 <a rel="nofollow" class="external text" href="http://www.boost.org/doc/libs/release/libs/assign/doc/index.html#intro">boost.assign</a>、boost.spirit 和其他库。数据库访问库 <a rel="nofollow" class="external text" href="http://soci.sourceforge.net/doc.html">SOCI</a> 亦重载 <code>operator,</code>。</p>
|
|
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
|
|
<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
|
|
<table class="dsctable" style="font-size:0.8em">
|
|
<tr>
|
|
<th>DR</th>
|
|
<th>应用于</th>
|
|
<th>出版时的行为</th>
|
|
<th>正确行为</th>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://wg21.cmeerw.net/cwg/issue1550">CWG 1550</a></td>
|
|
<td>C++98</td>
|
|
<td>当另一操作数并非 void 时 ?: 中不允许有括号的 throw 表达式</td>
|
|
<td>接受有括号的 throw 表达式</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://wg21.cmeerw.net/cwg/issue1560">CWG 1560</a></td>
|
|
<td>C++98</td>
|
|
<td> ?: 中的 void 操作数导致另一操作数上<br />
|
|
无理由的左值到右值转换，始终产生右值</td>
|
|
<td>带 void 的 ?: 能为左值</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://wg21.cmeerw.net/cwg/issue1932">CWG 1932</a></td>
|
|
<td>C++14</td>
|
|
<td> ?: 中缺失同类型位域</td>
|
|
<td>以底层类型处理</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://wg21.cmeerw.net/cwg/issue1895">CWG 1895</a></td>
|
|
<td>C++14</td>
|
|
<td>不明确弃置或不可访问的转换函数是否阻止 ?: 的转换，<br />
|
|
且未考虑从基类到派生类纯右值的转换</td>
|
|
<td>与重载决议相似的方式处理</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<p><a href="cpp-language-operator_precedence.html">运算符优先级</a></p>
|
|
<p><a href="cpp-language-operators.html">运算符重载</a></p>
|
|
<table class="wikitable">
|
|
<tr style="text-align:center">
|
|
<th colspan="7">常见运算符</th>
|
|
</tr>
|
|
<tr style="text-align:center">
|
|
<td><a href="cpp-language-operator_assignment.html">赋值</a></td>
|
|
<td><a href="cpp-language-operator_incdec.html">自增<br />
|
|
自减</a></td>
|
|
<td><a href="cpp-language-operator_arithmetic.html">算术</a></td>
|
|
<td><a href="cpp-language-operator_logical.html">逻辑</a></td>
|
|
<td><a href="cpp-language-operator_comparison.html">比较</a></td>
|
|
<td><a href="cpp-language-operator_member_access.html">成员访问</a></td>
|
|
<td><strong class="selflink">其他</strong></td>
|
|
</tr>
|
|
<tr style="text-align:center">
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">=</span> b<br />
|
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a <span class="sy2">+</span><span class="sy1">=</span> b<br />
|
|
a <span class="sy2">-</span><span class="sy1">=</span> b<br />
|
|
a <span class="sy2">*</span><span class="sy1">=</span> b<br />
|
|
a <span class="sy2">/</span><span class="sy1">=</span> b<br />
|
|
a <span class="sy2">%</span><span class="sy1">=</span> b<br />
|
|
a <span class="sy3">&</span><span class="sy1">=</span> b<br />
|
|
a <span class="sy3">|</span><span class="sy1">=</span> b<br />
|
|
a <span class="sy3">^</span><span class="sy1">=</span> b<br />
|
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a <span class="sy1"><<=</span> b<br />
|
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a <span class="sy1">>>=</span> b</span></span></p>
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</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>a<br />
|
|
<span class="sy2">--</span>a<br />
|
|
a<span class="sy2">++</span><br />
|
|
a<span class="sy2">--</span></span></span></p>
|
|
</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">+</span>a<br />
|
|
<span class="sy2">-</span>a<br />
|
|
a <span class="sy2">+</span> b<br />
|
|
a <span class="sy2">-</span> b<br />
|
|
a <span class="sy2">*</span> b<br />
|
|
a <span class="sy2">/</span> b<br />
|
|
a <span class="sy2">%</span> b<br />
|
|
~a<br />
|
|
a <span class="sy3">&</span> b<br />
|
|
a <span class="sy3">|</span> b<br />
|
|
a <span class="sy3">^</span> b<br />
|
|
a <span class="sy1"><<</span> b<br />
|
|
a <span class="sy1">>></span> b</span></span></p>
|
|
</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span>a<br />
|
|
a <span class="sy3">&&</span> b<br />
|
|
a <span class="sy3">||</span> b</span></span></p>
|
|
</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">==</span> b<br />
|
|
a <span class="sy3">!</span><span class="sy1">=</span> b<br />
|
|
a <span class="sy1"><</span> b<br />
|
|
a <span class="sy1">></span> b<br />
|
|
a <span class="sy1"><=</span> b<br />
|
|
a <span class="sy1">>=</span> b<br />
|
|
a <span class="sy1"><=></span> b</span></span></p>
|
|
</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>b<span class="br0">]</span><br />
|
|
<span class="sy2">*</span>a<br />
|
|
<span class="sy3">&</span>a<br />
|
|
a<span class="sy2">-</span><span class="sy1">></span>b<br />
|
|
a.<span class="me1">b</span><br />
|
|
a<span class="sy2">-</span><span class="sy1">></span><span class="sy2">*</span>b<br />
|
|
a.<span class="sy2">*</span>b</span></span></p>
|
|
</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">(</span>...<span class="br0">)</span><br />
|
|
a, b<br />
|
|
<span class="sy4">?</span> <span class="sy4">:</span></span></span></p>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<th colspan="7">特殊运算符</th>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="7">
|
|
<p><a href="cpp-language-static_cast.html"><tt>static_cast</tt></a> 转换一个类型为另一相关类型<br />
|
|
<a href="cpp-language-dynamic_cast.html"><tt>dynamic_cast</tt></a> 在继承层级中转换<br />
|
|
<a href="cpp-language-const_cast.html"><tt>const_cast</tt></a> 添加或移除 <a href="cpp-language-cv.html">cv</a> 限定符<br />
|
|
<a href="cpp-language-reinterpret_cast.html"><tt>reinterpret_cast</tt></a> 转换类型到无关类型<br />
|
|
<a href="cpp-language-explicit_cast.html">C 风格转型</a> 以 <code>static_cast</code> 、 <code>const_cast</code> 及 <code>reinterpret_cast</code> 的混合转换一个类型到另一类型<br />
|
|
<a href="cpp-language-new.html"><tt>new</tt></a> 创建有动态存储期的对象<br />
|
|
<a href="cpp-language-delete.html"><tt>delete</tt></a> 销毁先前由 new 表达式创建的对象，并释放其所拥有的内存区域<br />
|
|
<a href="cpp-language-sizeof.html"><tt>sizeof</tt></a> 查询类型的大小<br />
|
|
<a href="cpp-language-sizeof....html"><tt>sizeof...</tt></a> 查询<a href="cpp-language-parameter_pack.html">形参包</a>的大小<span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
|
|
<a href="cpp-language-typeid.html"><tt>typeid</tt></a> 查询类型的类型信息<br />
|
|
<a href="cpp-language-noexcept.html"><tt>noexcept</tt></a> 查询表达式是否能抛出异常<span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
|
|
<a href="cpp-language-alignof.html"><tt>alignof</tt></a> 查询类型的对齐要求<span class="t-mark-rev t-since-cxx11">(C++11 起)</span></p>
|
|
</td>
|
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</tr>
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</table>
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<table class="t-dsc-begin"></table>
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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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