561 lines
44 KiB
HTML
561 lines
44 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-c_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="c.html">c</a>‎ | <a href="c-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>不适合任何其他主要类别的运算符的汇集。</p>
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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<tr>
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<td class="mbox-empty-cell"></td>
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<td class="mbox-text" style="">本节未完成<br />
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原因：为这个和其他表格考虑更通用的，覆盖多个专题的 ToC</td>
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</tr>
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</table>
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<table class="wikitable" style="font-size:85%;">
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<tr style="text-align:center">
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<th>运算符</th>
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<th>运算符名</th>
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<th>示例</th>
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<th>描述</th>
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</tr>
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<tr style="text-align:center">
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<td><span class="t-c"><span class="mw-geshi c source-c"><span class="br0">(</span>...<span class="br0">)</span></span></span></td>
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<td><a href="c-language-operator_other.html#.E5.87.BD.E6.95.B0.E8.B0.83.E7.94.A8">函数调用</a></td>
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<td><span class="t-c"><span class="mw-geshi c source-c">f<span class="br0">(</span>...<span class="br0">)</span></span></span></td>
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<td>以令或更多参数调用 <b>f</b>()</td>
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</tr>
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<tr style="text-align:center">
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<td><span class="t-c"><span class="mw-geshi c source-c">,</span></span></td>
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<td><a href="c-language-operator_other.html#.E9.80.97.E5.8F.B7.E8.BF.90.E7.AE.97.E7.AC.A6">逗号运算符</a></td>
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<td><span class="t-c"><span class="mw-geshi c source-c">a, b</span></span></td>
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<td>求值表达式 <b>a</b> ，舍弃其返回值并完成任何副效应，然后求值表达式 <b>b</b> ，返回此求值的类型和结果</td>
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</tr>
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<tr style="text-align:center">
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<td><span class="t-c"><span class="mw-geshi c source-c"><span class="br0">(</span>type<span class="br0">)</span></span></span></td>
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<td><a href="c-language-cast.html">转型</a></td>
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<td><span class="t-c"><span class="mw-geshi c source-c"><span class="br0">(</span>type<span class="br0">)</span>a</span></span></td>
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<td>转型 <b>a</b> 的类型为 <b>type</b></td>
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</tr>
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<tr style="text-align:center">
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<td><span class="t-c"><span class="mw-geshi c source-c"><span class="sy4">?</span> <span class="sy4">:</span></span></span></td>
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<td><a href="c-language-operator_other.html#.E6.9D.A1.E4.BB.B6.E8.BF.90.E7.AE.97.E7.AC.A6">条件运算符</a></td>
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<td><span class="t-c"><span class="mw-geshi c source-c">a <span class="sy4">?</span> b <span class="sy4">:</span> c</span></span></td>
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<td>若 <b>a</b> 逻辑上为真（不求值为零）则求值表达式 <b>b</b> ，否则求值表达式 <b>c</b></td>
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</tr>
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<tr style="text-align:center">
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<td><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">sizeof</span></span></span></td>
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<td><a href="c-language-sizeof.html">sizeof 运算符</a></td>
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<td><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">sizeof</span> a</span></span></td>
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<td><b>a</b> 的字节大小</td>
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</tr>
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<tr style="text-align:center">
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<td><span class="t-c"><span class="mw-geshi c source-c">_Alignof</span></span> <span class="t-mark-rev t-since-c11">(C11 起)</span></td>
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<td><a href="c-language-_Alignof.html">_Alignof 运算符</a></td>
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<td><span class="t-c"><span class="mw-geshi c source-c">_Alignof<span class="br0">(</span>type<span class="br0">)</span></span></span></td>
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<td><b>type</b> 对齐</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.87.BD.E6.95.B0.E8.B0.83.E7.94.A8">函数调用</span></h3>
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<p>函数调用表达式拥有形式</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">expression</span> <code><b>(</b></code> <span class="t-spar">argument-list</span><span class="t-mark">(可选)</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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<table class="t-par-begin">
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<tr class="t-par">
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<td><span class="t-spar">expression</span></td>
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<td>-</td>
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<td>任何指向函数指针类型表达式（在<a href="c-language-conversion.html#.E5.B7.A6.E5.80.BC.E8.BD.AC.E6.8D.A2">左值转换</a>后）</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">argument-list</span></td>
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<td>-</td>
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<td>任何完整对象类型表达式（不能是逗号运算符）的逗号分隔列表。调用不接受参数的函数时可以省略。</td>
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</tr>
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</table>
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<p>函数调用表达式的行为，取决于正在调用的函数的原型是否在调用点处<a href="c-language-scope.html">于作用域中</a>。</p>
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<h4><span class="mw-headline" id=".E8.B0.83.E7.94.A8.E6.9C.89.E5.8E.9F.E5.9E.8B.E5.87.BD.E6.95.B0">调用有原型函数</span></h4>
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<div class="t-li1"><span class="t-li">1)</span> 形参数量必须等于实参数量（除非使用省略号形参）。</div>
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<div class="t-li1"><span class="t-li">2)</span> 必须存在<a href="c-language-conversion.html">如同赋值的隐式转换</a>，将对应实参的无限定类型转换为形参类型。</div>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-c99">
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<td>
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<div class="t-li1"><span class="t-li"></span> 另外，对于每个在 <code><b>[</b></code> 和 <code><b>]</b></code> 间使用关键词 <code>static</code> 的<a href="c-language-array.html">数组类型</a>形参，实参表达式所指代的数组元素数，必须不少于形参的大小表达式中指定的数量。</div>
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</td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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</tr>
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</table>
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<div class="t-li1"><span class="t-li">3)</span> <a href="c-language-eval_order.html">以未指定顺序无序地</a>求值实参。</div>
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<div class="t-li1"><span class="t-li">4)</span> 进行<span class="t-rev-inl t-until-c11"><span><a href="c-language-operator_assignment.html">赋值</a></span> <span><span class="t-mark-rev t-until-c11">(C11 前)</span></span></span><span class="t-rev-inl t-since-c11"><span><a href="c-language-initialization.html">初始化</a></span> <span><span class="t-mark-rev t-since-c11">(C11 起)</span></span></span>，复制每个实参到对应的函数形参（注意：函数能修改其形参，而这些修改不影响实参， C 函数调用只有以值调用）。
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<dl>
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<dd>
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<ul>
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<li>若有<a href="c-language-variadic.html">尾随省略号</a>形参，则在剩余实参上进行<a href="c-language-conversion.html#.E9.BB.98.E8.AE.A4.E5.8F.82.E6.95.B0.E6.8F.90.E5.8D.87">默认参数提升</a>，这使得它们可由 <span class="t-lc">va_list</span> 访问。</li>
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</ul>
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</dd>
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</dl>
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</div>
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<div class="t-li1"><span class="t-li">5)</span> 执行函数，而其返回值成为函数调用表达式的值（若函数返回 void ，则函数调用表达式为 void 表达式）。
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1"><span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">char</span><span class="sy2">*</span> p, <span class="kw4">int</span> x<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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f<span class="br0">(</span><span class="st0">"abc"</span>, <span class="nu16">3.14</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 数组到指针和 float 到 int 转换</span>
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<span class="br0">}</span></pre></div>
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</div>
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</div>
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<h4><span class="mw-headline" id=".E8.B0.83.E7.94.A8.E6.97.A0.E5.8E.9F.E5.9E.8B.E5.87.BD.E6.95.B0">调用无原型函数</span></h4>
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<div class="t-li1"><span class="t-li">1)</span> <a href="c-language-eval_order.html">以未指定顺序无序地</a>求值实参。</div>
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<div class="t-li1"><span class="t-li">2)</span> 在每个实参表达式上进行<a href="c-language-conversion.html#.E9.BB.98.E8.AE.A4.E5.8F.82.E6.95.B0.E6.8F.90.E5.8D.87">默认参数提升</a>。</div>
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<div class="t-li1"><span class="t-li">3)</span> 进行<span class="t-rev-inl t-until-c11"><span><a href="c-language-operator_assignment.html">赋值</a></span> <span><span class="t-mark-rev t-until-c11">(C11 前)</span></span></span><span class="t-rev-inl t-since-c11"><span><a href="c-language-initialization.html">初始化</a></span> <span><span class="t-mark-rev t-since-c11">(C11 起)</span></span></span>，复制每个实参到对应的函数形参。</div>
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<div class="t-li1"><span class="t-li">4)</span> 执行函数，而其所返回的值成为函数调用表达式的值（若函数返回 void ，则函数调用表达式为 void 表达式）
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1"><span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 无原型</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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f<span class="br0">(</span><span class="nu0">1</span>, <span class="nu17">1.0f</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// UB ，除非定义 f 为接收一个 int 和一个 double</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">int</span> a, <span class="kw4">double</span> c<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></pre></div>
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</div>
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</div>
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<p>调用无原型函数的行为未定义，若</p>
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<ul>
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<li>实参数量不匹配形参数量</li>
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<li>提升后的实参类型与提升后形参类型不<a href="c-language-types.html#.E5.85.BC.E5.AE.B9.E7.B1.BB.E5.9E.8B">兼容</a>，除了</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>认为相同整数类型的有符号和无符号版本兼容，若参数值能以两个类型表示。</li>
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<li>认为指向 void 指针和指向（可有 cvr 限定的）字符类型指针兼容</li>
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</ul>
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</dd>
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</dl>
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<h4><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h4>
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<p>指代要调用的函数的 <span class="t-spar">expression</span> 和所有参数的求值相对于彼此<a href="c-language-eval_order.html">无序</a>（但在函数开始执行前有一个序列点）</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1"><span class="br0">(</span><span class="sy2">*</span>pf<span class="br0">[</span>f1<span class="br0">(</span><span class="br0">)</span><span class="br0">]</span><span class="br0">)</span> <span class="br0">(</span>f2<span class="br0">(</span><span class="br0">)</span>, f3<span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> f4<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 可以以任何顺序调用 f1 、 f2 、 f3 、 f4</span></pre></div>
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</div>
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<p>尽管函数调用只对指向函数指针定义，它亦能作用于函数指代器，因为<a href="c-language-conversion.html#.E5.87.BD.E6.95.B0.E5.88.B0.E6.8C.87.E9.92.88.E8.BD.AC.E6.8D.A2">函数到指针隐式转换</a>。</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1"><span class="kw4">int</span> f<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="br0">}</span>
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<span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>pf<span class="br0">)</span><span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="sy1">=</span> f<span class="sy4">;</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</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">// 转换 f 为指针，然后调用</span>
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<span class="br0">(</span><span class="sy3">&</span>f<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 创建指向函数指针，然后调用</span>
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pf<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 调用函数</span>
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<span class="br0">(</span><span class="sy2">*</span>pf<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 获得函数指代器，转换为指针，然后滴啊用、</span>
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<span class="br0">(</span><span class="sy2">****</span>f<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 转换为指针，获得函数，重复 4 次，然后调用</span>
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<span class="br0">(</span><span class="sy2">****</span>pf<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 亦 OK</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>必须用在作用域中的原型调用忽略不使用实参的函数，如 <span class="t-lc"><a href="c-io-fprintf.html">printf</a></span> （这种函数的原型需要使用<a href="c-language-variadic.html">尾随省略号</a>形参），以避免未定义行为。</p>
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<p>C11 后缺陷报告 DR 427 将在调用有原型的函数时的函数形参准备，从赋值自其对应实参，更改为从其对应实参初始化，以允许 const 限定类型的形参（<i>事实上</i>已允许）。容许的隐式转换仍为如同赋值的转换，因为<a href="c-language-initialization.html">初始化</a>亦使用这些。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-until-c99">
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<td>
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<p>其 <span class="t-spar">expression</span> 完全由一个标识符组成，而未声明该标识符的函数调用表达式，表现为通过将该标识符声明如下</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1"><span class="kw2">extern</span> <span class="kw4">int</span> identifier<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 返回 int 且无原型</span></pre></div>
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</div>
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<p>故下列完整程序在 C89 中合法：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1">main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">int</span> n <span class="sy1">=</span> <a href="c-string-byte-atoi.html"><span class="kw541">atoi</span></a><span class="br0">(</span><span class="st0">"123"</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 隐式声明 atoi 为 int atoi()</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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<td><span class="t-mark-rev t-until-c99">(C99 前)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E9.80.97.E5.8F.B7.E8.BF.90.E7.AE.97.E7.AC.A6">逗号运算符</span></h3>
|
|
<p>逗号运算符表达式拥有形式</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">lhs</span> <code><b>,</b></code> <span class="t-spar">rhs</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>其中</p>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td><span class="t-spar">lhs</span></td>
|
|
<td>-</td>
|
|
<td>任何表达式</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td><span class="t-spar">rhs</span></td>
|
|
<td>-</td>
|
|
<td>任何异于另一逗号运算符的表达式（换言之，逗号运算符的<a href="c-language-operator_precedence.html">结合性</a>为从左到右）</td>
|
|
</tr>
|
|
</table>
|
|
<p>首先，求值左运算数 <span class="t-spar">lhs</span> 并舍弃其结果值。</p>
|
|
<p>然后，发生<a href="c-language-eval_order.html">序列点</a>，从而 <span class="t-spar">lhs</span> 的所有副效应完成。</p>
|
|
<p>然后，求值右运算数 <span class="t-spar">rhs</span> ，而逗号运算符作为<a href="c-language-value_category.html">非左值</a>返回其结果。</p>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F_2">注意</span></h3>
|
|
<p><span class="t-spar">lhs</span> 的类型可为 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span></span></span> （即可为对返回 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span></span></span> 的函数的调用，或能为 <a href="c-language-cast.html">转型</a>到 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span></span></span> 的表达式）。</p>
|
|
<p>逗号运算符在 C++ 中可为左值，但 C 中决不是。</p>
|
|
<p>逗号运算符可返回结构体（其他返回结构体的表达式仅有复合字面量、函数调用、赋值和条件运算符）。</p>
|
|
<p>下列语境中，逗号运算符不能出现于表达式的顶层，因为逗号有不同含义：</p>
|
|
<ul>
|
|
<li>函数调用中的实参列表</li>
|
|
<li>初始化器表达式或<a href="c-language-initialization.html">初始化器列表</a></li>
|
|
<li><a href="c-language-generic.html">泛型选择</a></li>
|
|
</ul>
|
|
<p>若必须在这种语境中使用逗号运算符，则必须加括号：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="co1">// int n = 2,3; // 错误：认为逗号开始下个声明器</span>
|
|
<span class="co1">// int a[2] = {1,2,3}; // 错误：初始化器多于元素</span>
|
|
<span class="kw4">int</span> n <span class="sy1">=</span> <span class="br0">(</span><span class="nu0">2</span>,<span class="nu0">3</span><span class="br0">)</span>, a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span><span class="br0">(</span><span class="nu0">1</span>,<span class="nu0">2</span><span class="br0">)</span>,<span class="nu0">3</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
|
|
f<span class="br0">(</span>a, <span class="br0">(</span>t<span class="sy1">=</span><span class="nu0">3</span>, t<span class="sy2">+</span><span class="nu0">2</span><span class="br0">)</span>, c<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK ：存储 3 于 t ，然后以三个参数调用 f</span></pre></div>
|
|
</div>
|
|
<p>数组边界中亦禁止顶层逗号</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="co1">// int a[2,3]; // 错误</span>
|
|
<span class="kw4">int</span> a<span class="br0">[</span><span class="br0">(</span><span class="nu0">2</span>,<span class="nu0">3</span><span class="br0">)</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// OK ：大小为 3 的 VLA 数组（因为 (2, 3) 不是常量表达式故为 VLA ）</span></pre></div>
|
|
</div>
|
|
<p><a href="c-language-constant_expression.html">常量表达式</a>中不允许逗号，不管它是否出现于顶层</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="co1">// static int n = (1,2); // 错误：常量表达式不能调用逗号运算符</span></pre></div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E8.BD.AC.E5.9E.8B.E8.BF.90.E7.AE.97.E7.AC.A6">转型运算符</span></h3>
|
|
<p>见<a href="c-language-cast.html">转型运算符</a></p>
|
|
<h3><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></h3>
|
|
<p>条件运算符表达式拥有形式</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">condition</span> <code><b>?</b></code> <span class="t-spar">expression-true</span> <code><b>:</b></code> <span class="t-spar">expression-false</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>其中</p>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td><span class="t-spar">condition</span></td>
|
|
<td>-</td>
|
|
<td>标量类型表达式</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td><span class="t-spar">expression-true</span></td>
|
|
<td>-</td>
|
|
<td>若条件比较不等于零则将求值的表达式</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td><span class="t-spar">expression-false</span></td>
|
|
<td>-</td>
|
|
<td>若条件比较等于零则将求值的表达式</td>
|
|
</tr>
|
|
</table>
|
|
<p>仅允许下列表达式为 <span class="t-spar">expression-true</span> 和 <span class="t-spar">expression-false</span></p>
|
|
<ul>
|
|
<li>二个任何<a href="c-language-arithmetic_types.html">算术</a>类型的表达式</li>
|
|
<li>二个相同<a href="c-language-struct.html">结构体</a>或<a href="c-language-union.html">联合体</a>类型的表达式</li>
|
|
<li>二个 void 类型表达式</li>
|
|
<li>二个指针类型表达式，指向<a href="c-language-types.html#.E5.85.BC.E5.AE.B9.E7.B1.BB.E5.9E.8B">兼容</a>的类型，忽略 cvr 限定符</li>
|
|
<li>一个表达式是指针而另一个是空指针常量（例如 <span class="t-lc"><a href="c-types-NULL.html">NULL</a></span> ）</li>
|
|
<li>一个表达式是指向对象指针而另一个是指向 void （可有限定）指针</li>
|
|
</ul>
|
|
<div class="t-li1"><span class="t-li">1)</span> 首先，求值 <span class="t-spar">condition</span> 。此求值后有<a href="c-language-eval_order.html">序列点</a>。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 若 <span class="t-spar">condition</span> 的结果比较等于零，则执行 <span class="t-spar">expression-true</span> ，否则执行 <span class="t-spar">exception-false</span> 。</div>
|
|
<div class="t-li1"><span class="t-li">3)</span> 进行从结果到<i>公共类型</i>的<a href="c-language-conversion.html">转换</a>，转换定义如下：</div>
|
|
<div class="t-li2"><span class="t-li">1)</span> 若表达式拥有算术类型，则公共类型为<a href="c-language-conversion.html#.E9.80.9A.E5.B8.B8.E7.AE.97.E6.9C.AF.E8.BD.AC.E6.8D.A2">通常算术转换</a>后的类型</div>
|
|
<div class="t-li2"><span class="t-li">2)</span> 若表达式拥有结构体/联合体类型，则公共类型为结构体/联合体类型</div>
|
|
<div class="t-li2"><span class="t-li">3)</span> 若表达式都是 void ，则整个条件运算符表达式就是 void 表达式</div>
|
|
<div class="t-li2"><span class="t-li">4)</span> 若一个表达式为指针而另一个是空指针常量，则类型为该指针的类型</div>
|
|
<div class="t-li2"><span class="t-li">5)</span> 若两个表达式都是指针，则结果为指向组合两个被指向类型的 cvr 限定符的类型的指针（即若一个指针是 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">*</span></span></span> 而另一个是 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">volatile</span> <span class="kw4">int</span><span class="sy2">*</span></span></span> ，则结果为 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">const</span> <span class="kw4">volatile</span> <span class="kw4">int</span><span class="sy2">*</span></span></span> ），而假如类型不同，则被指向类型为两类型的<a href="c-language-types.html#.E5.90.88.E6.88.90.E7.B1.BB.E5.9E.8B">合成类型</a>。</div>
|
|
<div class="t-li2"><span class="t-li">6)</span> 若一个表达式是指向 void 指针，则结果为指向带组合的 cvr 限定符的 void 的指针。</div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="co2">#define ICE(x) (sizeof(*(1 ? ((void*)((x) * 0l)) : (int*)1)))</span>
|
|
|
|
<span class="co1">// 若 x 是整数常量表达式，则宏展开成</span>
|
|
|
|
<span class="kw4">sizeof</span><span class="br0">(</span> <span class="nu0">1</span> <span class="sy4">?</span> <a href="c-types-NULL.html"><span class="kw103">NULL</span></a> <span class="sy4">:</span> <span class="br0">(</span><span class="kw4">int</span> <span class="sy2">*</span><span class="br0">)</span> <span class="nu0">1</span><span class="br0">)</span> <span class="co1">// (void *)((x)*0l)) -> NULL</span>
|
|
|
|
<span class="co1">// 按照第 (4) 点这进一步转换成</span>
|
|
|
|
<span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span>
|
|
|
|
<span class="co1">// 若 x 不是整数常量表达式，则宏按照第 (6) 点展开成</span>
|
|
|
|
<span class="br0">(</span><span class="kw4">sizeof</span><span class="br0">(</span><span class="sy2">*</span><span class="br0">(</span><span class="kw4">void</span> <span class="sy2">*</span><span class="br0">)</span><span class="br0">(</span>x<span class="br0">)</span><span class="br0">)</span> <span class="co1">// 因不完整类型而错误</span></pre></div>
|
|
</div>
|
|
<h4><span class="mw-headline" id=".E6.B3.A8.E6.84.8F_3">注意</span></h4>
|
|
<p>条件运算符决不是<a href="c-language-value_category.html">左值表达式</a>，尽管它可以返回结构体/联合体类型的对象。其他可以返回结构体的表达式仅有<a href="c-language-operator_assignment.html">赋值</a>、<a href="c-language-operator_other.html#.E9.80.97.E5.8F.B7.E8.BF.90.E7.AE.97.E7.AC.A6">逗号</a>、<a href="c-language-operator_other.html#.E5.87.BD.E6.95.B0.E8.B0.83.E7.94.A8">函数调用</a>和<a href="c-language-compound_literal.html">复合字面量</a>。</p>
|
|
<p>注意 C++ 中它可以为左值表达式。</p>
|
|
<p>此运算符和赋值的相对优先级上的细节见<a href="c-language-operator_precedence.html">运算符优先级</a>。</p>
|
|
<p>条件运算符拥有从右到左结合性，这允许链式写法</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="kw1">struct</span> vehicle v <span class="sy1">=</span> arg <span class="sy1">==</span> <span class="st0">'B'</span> <span class="sy4">?</span> bus <span class="sy4">:</span>
|
|
arg <span class="sy1">==</span> <span class="st0">'A'</span> <span class="sy4">?</span> airplane <span class="sy4">:</span>
|
|
arg <span class="sy1">==</span> <span class="st0">'T'</span> <span class="sy4">?</span> train <span class="sy4">:</span>
|
|
arg <span class="sy1">==</span> <span class="st0">'C'</span> <span class="sy4">?</span> car <span class="sy4">:</span>
|
|
arg <span class="sy1">==</span> <span class="st0">'H'</span> <span class="sy4">?</span> horse <span class="sy4">:</span>
|
|
feet<span class="sy4">;</span></pre></div>
|
|
</div>
|
|
<h3><span class="mw-headline" id="sizeof_.E8.BF.90.E7.AE.97.E7.AC.A6">sizeof 运算符</span></h3>
|
|
<p>见 <a href="c-language-sizeof.html">sizeof 运算符</a></p>
|
|
<h3><span class="mw-headline" id="Alignof_.E8.BF.90.E7.AE.97.E7.AC.A6">_Alignof 运算符</span></h3>
|
|
<p>见 <a href="c-language-_Alignof.html">_Alignof 运算符</a></p>
|
|
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
|
|
<div class="t-ref-std-11">
|
|
<ul>
|
|
<li>C11 标准（ISO/IEC 9899:2011）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.2.2 Function calls (p: 81-82)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.3.4 The sizeof and _Alignof operators (p: 90-91)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.4 Cast operators (p: 91)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.15 Conditional operator (p: 100)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.17 Comma operator (p: 105)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<div class="t-ref-std-c99">
|
|
<ul>
|
|
<li>C99 标准（ISO/IEC 9899:1999）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.2.2 Function calls (p: 71-72)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.3.4 The sizeof operator (p: 80-81)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.4 Cast operators (p: 81)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.15 Conditional operator (p: 90-91)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.5.17 Comma operator (p: 94)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<div class="t-ref-std-c89">
|
|
<ul>
|
|
<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>3.3.2.2 Function calls</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>3.3.3.4 The sizeof operator</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>3.3.4 Cast operators</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>3.3.15 Conditional operator</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>3.3.17 Comma operator</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<ul>
|
|
<li><a href="c-language-operator_precedence.html">运算符优先级</a></li>
|
|
</ul>
|
|
<table class="wikitable">
|
|
<tr style="text-align:center">
|
|
<th colspan="7">常用运算符</th>
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</tr>
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<tr style="text-align:center">
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<td><a href="c-language-operator_assignment.html">赋值</a></td>
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<td><a href="c-language-operator_incdec.html">自增<br />
|
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自减</a></td>
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<td><a href="c-language-operator_arithmetic.html">算术</a></td>
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|
<td><a href="c-language-operator_logical.html">逻辑</a></td>
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<td><a href="c-language-operator_comparison.html">比较</a></td>
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<td><a href="c-language-operator_member_access.html">成员<br />
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|
访问</a></td>
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|
<td><strong class="selflink">其他</strong></td>
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</tr>
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<tr style="text-align:center">
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<td>
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<p><span class="t-c"><span class="mw-geshi c source-c">a <span class="sy1">=</span> b<br />
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a <span class="sy2">+</span><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="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="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>
|
|
</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi c source-c"><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>
|
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<p><span class="t-c"><span class="mw-geshi c source-c"><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 c source-c"><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 c source-c">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</span></span></p>
|
|
</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi c source-c">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></span></span></p>
|
|
</td>
|
|
<td>
|
|
<p><span class="t-c"><span class="mw-geshi c source-c">a<span class="br0">(</span>...<span class="br0">)</span><br />
|
|
a, b<br />
|
|
<span class="br0">(</span>type<span class="br0">)</span> a<br />
|
|
<span class="sy4">?</span> <span class="sy4">:</span><br />
|
|
<span class="kw4">sizeof</span><br />
|
|
_Alignof</span></span> <span class="t-mark-rev t-since-c11">(C11 起)</span></p>
|
|
</td>
|
|
</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>
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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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