366 lines
21 KiB
HTML
366 lines
21 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>逻辑运算符</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_logical 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">逻辑运算符</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>逻辑运算符应用标准布尔代数运算到其运算数。</p>
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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>结果</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="sy3">!</span></span></span></td>
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<td>逻辑非</td>
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<td><span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">!</span>a</span></span></td>
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<td><b>a</b> 的逻辑否定</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="sy3">&&</span></span></span></td>
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<td>逻辑与</td>
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<td><span class="t-c"><span class="mw-geshi c source-c">a <span class="sy3">&&</span> b</span></span></td>
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<td><b>a</b> 与 <b>b</b> 的逻辑与</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="sy3">||</span></span></span></td>
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<td>逻辑或</td>
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<td><span class="t-c"><span class="mw-geshi c source-c">a <span class="sy3">||</span> b</span></span></td>
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<td><b>a</b> 与 <b>b</b> 的逻辑或</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E9.80.BB.E8.BE.91.E9.9D.9E">逻辑非</span></h3>
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<p>逻辑非运算符拥有形式</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"><code><b>!</b></code> <span class="t-spar">expression</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>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>拥有任何<a href="c-language-type.html#.E7.B1.BB.E5.9E.8B.E7.BB.84.E5.88.AB" class="mw-redirect">标量类型</a>的表达式</td>
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</tr>
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</table>
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<p>逻辑非运算符拥有 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span> 类型。若 <span class="t-spar">expression</span> 求值为不等于零的整数则其值为 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> 。若 <span class="t-spar">expression</span> 求值为等于零的整数则其值为 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 。（故 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">!</span>E</span></span> 与 {{c|(0==E)} 相同）</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="c source-c">
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<pre class="de1"><span class="co2">#include <stdbool.h></span>
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<span class="co2">#include <stdio.h></span>
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<span class="co2">#include <ctype.h></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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bool b <span class="sy1">=</span> <span class="sy3">!</span><span class="br0">(</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="br0">)</span><span class="sy4">;</span> <span class="co1">// 非 true</span>
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<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"!(2+2==4) = %s<span class="es1">\n</span>"</span>, b <span class="sy4">?</span> <span class="st0">"true"</span> <span class="sy4">:</span> <span class="st0">"false"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> n <span class="sy1">=</span> <a href="c-string-byte-isspace.html"><span class="kw534">isspace</span></a><span class="br0">(</span><span class="st0">'a'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 若 'a' 空格则为零，否则为非零</span>
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<span class="kw4">int</span> x <span class="sy1">=</span> <span class="sy3">!!</span>n<span class="sy4">;</span> <span class="co1">// "bang-bang" ，常用的 C 手法，映射标量为 [0,1]</span>
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<span class="co1">// （所有非零值变为 1 ）</span>
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<span class="kw4">char</span> <span class="sy2">*</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="st0">"nonspace"</span>, <span class="st0">"space"</span><span class="br0">}</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%s<span class="es1">\n</span>"</span>, a<span class="br0">[</span>x<span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 现在能安全地以 x 为 2 个 int 的数组的下标</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">!(2+2==4) = false
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nonspace</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E9.80.BB.E8.BE.91.E4.B8.8E">逻辑与</span></h3>
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<p>逻辑与表达式拥有形式</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">lhs</span> <code><b>&&</b></code> <span class="t-spar">rhs</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>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">lhs</span></td>
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<td>-</td>
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<td>拥有任何标量类型的表达式</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">rhs</span></td>
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<td>-</td>
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<td>拥有任何标量类型的表达式，仅若 <span class="t-spar">lhs</span> 比较不等于 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> 才求值</td>
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</tr>
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</table>
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<p>逻辑与运算符拥有 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span> 类型，而若 <span class="t-spar">lhs</span> 与 <span class="t-spar">rhs</span> 都比较不等于零则拥有值 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 。否则拥有值 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> （若 <span class="t-spar">lhs</span> 或 <span class="t-spar">rhs</span> 之一或两者比较等于零）。</p>
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<p>在 <span class="t-spar">lhs</span> 的求值后有<a href="c-language-eval_order.html">序列点</a>。若 <span class="t-spar">lhs</span> 的结果比较等于零，则完全不求值 <span class="t-spar">rhs</span> （是谓<i>短路求值</i>）。</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="c source-c">
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<pre class="de1"><span class="co2">#include <stdbool.h></span>
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<span class="co2">#include <stdio.h></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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bool b <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="sy3">&&</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="co1">// b == true</span>
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<span class="nu0">1</span> <span class="sy1">></span> <span class="nu0">2</span> <span class="sy3">&&</span> <a href="c-io-puts.html"><span class="kw836">puts</span></a><span class="br0">(</span><span class="st0">"this won't print"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">char</span> <span class="sy2">*</span>p <span class="sy1">=</span> <span class="st0">"abc"</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>p <span class="sy3">&&</span> <span class="sy2">*</span>p<span class="br0">)</span> <span class="co1">// 常用的 C 手法：若 p 非空 *与* 若 p 不指向字符串尾</span>
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<span class="br0">{</span> <span class="co1">// （注意拜短路求值所赐，这不会试图解引用空指针）</span>
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<span class="co1">// ... // ……然后做一些字符串处理</span>
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<span class="br0">}</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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<h3><span class="mw-headline" id=".E9.80.BB.E8.BE.91.E6.88.96">逻辑或</span></h3>
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<p>逻辑或表达式拥有形式</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">lhs</span> <code><b>||</b></code> <span class="t-spar">rhs</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>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">lhs</span></td>
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<td>-</td>
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<td>拥有任何标量类型的表达式</td>
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</tr>
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<tr class="t-par">
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<td><span class="t-spar">rhs</span></td>
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<td>-</td>
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<td>拥有任何标量类型的表达式，仅若 <span class="t-spar">lhs</span> 比较等于 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> 才求值</td>
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</tr>
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</table>
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<p>逻辑或运算符拥有 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span> 类型，而若 <span class="t-spar">lhs</span> 或 <span class="t-spar">rhs</span> 比较不等于零则拥有值 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 。否则它拥有值 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> （若 <span class="t-spar">lhs</span> 与 <span class="t-spar">rhs</span> 都比较等于零）、</p>
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<p>在 <span class="t-spar">lhs</span> 的求值后有<a href="c-language-eval_order.html">序列点</a>。若 <span class="t-spar">lhs</span> 的结果比较不等于零，则完全不求值 <span class="t-spar">rhs</span> （是谓<i>短路求值</i>）。</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="c source-c">
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<pre class="de1"><span class="co2">#include <stdbool.h></span>
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<span class="co2">#include <stdio.h></span>
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<span class="co2">#include <string.h></span>
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<span class="co2">#include <errno.h></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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bool b <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="sy3">||</span> <span class="nu0">2</span><span class="sy2">+</span><span class="nu0">2</span> <span class="sy1">==</span> <span class="nu0">5</span><span class="sy4">;</span> <span class="co1">// true</span>
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<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"true or false = %s<span class="es1">\n</span>"</span>, b <span class="sy4">?</span> <span class="st0">"true"</span> <span class="sy4">:</span> <span class="st0">"false"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 逻辑或能像 perl 的 "or die" 一样使用，只要 rhs 拥有标量类型</span>
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<a href="c-io-fopen.html"><span class="kw819">fopen</span></a><span class="br0">(</span><span class="st0">"test.txt"</span>, <span class="st0">"r"</span><span class="br0">)</span> <span class="sy3">||</span> <a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"could not open test.txt: %s<span class="es1">\n</span>"</span>, <a href="c-string-byte-strerror.html"><span class="kw574">strerror</span></a><span class="br0">(</span><span class="kw2">errno</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出：</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">true or false = true
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could not open test.txt: No such file or directory</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准（ISO/IEC 9899:2011）：</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>6.5.3.3 Unary arithmetic operators (p: 89)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>6.5.13 Logical AND operator (p: 99)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>6.5.14 Logical OR operator (p: 99)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准（ISO/IEC 9899:1999）：</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>6.5.3.3 Unary arithmetic operators (p: 79)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>6.5.13 Logical AND operator (p: 89)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>6.5.14 Logical OR operator (p: 89)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c89">
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<ul>
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<li>C89/C90 标准（ISO/IEC 9899:1990）：</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>3.3.3.3 Unary arithmetic operators</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>3.3.13 Logical AND operator</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>3.3.14 Logical OR operator</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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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<p><a href="c-language-operator_precedence.html">运算符优先级</a></p>
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<table class="wikitable">
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<tr style="text-align:center">
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<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><strong class="selflink">逻辑</strong></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><a href="c-language-operator_other.html">其他</a></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 />
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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 />
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a <span class="sy2">%</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="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>
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</td>
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<td>
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<p><span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">++</span>a<br />
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<span class="sy2">--</span>a<br />
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a<span class="sy2">++</span><br />
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a<span class="sy2">--</span></span></span></p>
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</td>
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<td>
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<p><span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">+</span>a<br />
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<span class="sy2">-</span>a<br />
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a <span class="sy2">+</span> b<br />
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a <span class="sy2">-</span> b<br />
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a <span class="sy2">*</span> b<br />
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a <span class="sy2">/</span> b<br />
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a <span class="sy2">%</span> b<br />
|
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~a<br />
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a <span class="sy3">&</span> b<br />
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a <span class="sy3">|</span> b<br />
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a <span class="sy3">^</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>
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<td>
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<p><span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">!</span>a<br />
|
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a <span class="sy3">&&</span> b<br />
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a <span class="sy3">||</span> b</span></span></p>
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|
</td>
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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="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<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>
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<td>
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<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 />
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|
<span class="sy3">&</span>a<br />
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|
a<span class="sy2">-</span><span class="sy1">></span>b<br />
|
|
a.<span class="me1">b</span></span></span></p>
|
|
</td>
|
|
<td>
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<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>
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</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>
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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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</body>
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</html>
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