89 lines
8.5 KiB
HTML
89 lines
8.5 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>break 语句</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_break 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">break 语句</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-language.html">language</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<p>导致外围的 <a href="cpp-language-for.html">for</a>、<a href="cpp-language-range-for.html">范围 for</a>、<a href="cpp-language-while.html">while</a> 或 <a href="cpp-language-do.html">do-while</a> 循环或 <a href="cpp-language-switch.html">switch 语句</a>终止。</p>
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<p>在用条件表达式和条件语句终止循环显得笨拙时使用。</p>
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<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
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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 class="t-sdsc">
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<td class="t-sdsc-nopad"><span class="t-spar">属性</span><span class="t-mark">(可选)</span> <code><b>break</b></code> <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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</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>此语句之后，控制将被转移到紧跟其外围循环或 switch 的下一位置。与退出任何代码块一样，在执行外围循环之后的下一行之前，所有在外围复合语句或循环/switch 的 <span class="t-spar">条件</span> 中声明的具有自动存储期的变量，按照它们构造的逆序销毁。</p>
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<h3><span class="mw-headline" id=".E5.85.B3.E9.94.AE.E8.AF.8D">关键词</span></h3>
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<p><a href="cpp-keyword-break.html"><tt>break</tt></a></p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>break 语句不能用于跳出多重嵌套循环。这种情况可以使用 <a href="cpp-language-goto.html">goto 语句</a>。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">2</span><span class="sy4">;</span>
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<span class="kw1">switch</span> <span class="br0">(</span>i<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">case</span> <span class="nu0">1</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">"1"</span><span class="sy4">;</span> <span class="co1">//<---- 可能会有警告：直落</span>
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<span class="kw1">case</span> <span class="nu0">2</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">"2"</span><span class="sy4">;</span> <span class="co1">//从此 case 标号开始执行（+警告）</span>
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<span class="kw1">case</span> <span class="nu0">3</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">"3"</span><span class="sy4">;</span> <span class="co1">//<---- 可能会有警告：直落</span>
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<span class="kw1">case</span> <span class="nu0">4</span><span class="sy4">:</span> <span class="co1">//<---- 可能会有警告：直落</span>
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<span class="kw1">case</span> <span class="nu0">5</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">"45"</span><span class="sy4">;</span>
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<span class="kw1">break</span><span class="sy4">;</span> <span class="co1">//终止后续语句的执行</span>
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<span class="kw1">case</span> <span class="nu0">6</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">"6"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> j <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> j <span class="sy1"><</span> <span class="nu0">2</span><span class="sy4">;</span> j<span class="sy2">++</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> k <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> k <span class="sy1"><</span> <span class="nu0">5</span><span class="sy4">;</span> k<span class="sy2">++</span><span class="br0">)</span> <span class="br0">{</span> <span class="co1">// break 只会影响此循环</span>
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<span class="kw1">if</span> <span class="br0">(</span>k <span class="sy1">==</span> <span class="nu0">2</span><span class="br0">)</span> <span class="kw1">break</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> j <span class="sy1"><<</span> k <span class="sy1"><<</span> <span class="st0">" "</span><span class="sy4">;</span>
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<span class="br0">}</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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<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">2345
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00 01 10 11</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<td><code>[[<a href="cpp-language-attributes-fallthrough.html">fallthrough</a>]]</code><span class="t-mark-rev t-since-cxx17">(C++17)</span></td>
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<td>指示从上一个 case 标签的直落是有意的，会对直落进行警告的编译器不应对此进行诊断</td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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