84 lines
7.0 KiB
HTML
84 lines
7.0 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>C 属性： fallthrough (C23 起)</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_language_attributes_fallthrough skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">C 属性：</span> fallthrough <span class="t-mark-rev t-since-c23">(C23 起)</span></h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-language.html">language</a>‎ | <a href="c-language-attributes.html">attributes</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<p>指示从前一标号直落是有意的，而在发生直落时给出警告的编译器不应诊断它。</p>
|
|
<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
|
|
<table class="t-sdsc-begin">
|
|
<tr>
|
|
<td colspan="10" class="t-sdsc-sep"></td>
|
|
</tr>
|
|
<tr class="t-sdsc">
|
|
<td class="t-sdsc-nopad"><code><b>[[</b></code> <code><b>fallthrough</b></code> <code><b>]]</b></code><br />
|
|
<code><b>[[</b></code> <code><b>__fallthrough__</b></code> <code><b>]]</b></code></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>
|
|
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
|
|
<p>仅可用于<a href="c-language-declarations.html">属性声明</a>以创建<i>直落声明</i>（<span class="t-c"><span class="mw-geshi c source-c"><span class="br0">[</span><span class="br0">[</span>fallthrough<span class="br0">]</span><span class="br0">]</span><span class="sy4">;</span></span></span>）。</p>
|
|
<p>直落声明仅可用于 <a href="cpp-language-switch.html"><tt>switch</tt></a> 语句中，其中要遇到的下个块项（语句、声明或标号）是该 <code>switch</code> 语句的带 <code>case</code> 或 <code>default</code> 标号的语句。</p>
|
|
<p>指示从前一标号直落是有意的，而在发生直落时给出警告的编译器不应诊断它。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="co2">#include <stdbool.h></span>
|
|
|
|
<span class="kw4">void</span> g<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
|
|
<span class="kw4">void</span> h<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
|
|
<span class="kw4">void</span> i<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
|
|
|
|
<span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">int</span> n<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">switch</span> <span class="br0">(</span>n<span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="kw1">case</span> <span class="nu0">1</span><span class="sy4">:</span>
|
|
<span class="kw1">case</span> <span class="nu0">2</span><span class="sy4">:</span>
|
|
g<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">[</span><span class="br0">[</span>fallthrough<span class="br0">]</span><span class="br0">]</span><span class="sy4">;</span>
|
|
<span class="kw1">case</span> <span class="nu0">3</span><span class="sy4">:</span> <span class="co1">// 直落时不警告</span>
|
|
h<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">case</span> <span class="nu0">4</span><span class="sy4">:</span> <span class="co1">// 编译器可在发生直落时警告</span>
|
|
<span class="kw1">if</span><span class="br0">(</span>n <span class="sy1"><</span> <span class="nu0">3</span><span class="br0">)</span> <span class="br0">{</span>
|
|
i<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">[</span><span class="br0">[</span>fallthrough<span class="br0">]</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// OK</span>
|
|
<span class="br0">}</span>
|
|
<span class="kw1">else</span> <span class="br0">{</span>
|
|
<span class="kw1">return</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<span class="kw1">case</span> <span class="nu0">5</span><span class="sy4">:</span>
|
|
<span class="kw1">while</span> <span class="br0">(</span><span class="kw2">false</span><span class="br0">)</span> <span class="br0">{</span>
|
|
<span class="br0">[</span><span class="br0">[</span>fallthrough<span class="br0">]</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// 谬构：下一语句不是同一迭代的一部分</span>
|
|
<span class="br0">}</span>
|
|
<span class="kw1">case</span> <span class="nu0">6</span><span class="sy4">:</span>
|
|
<span class="br0">[</span><span class="br0">[</span>fallthrough<span class="br0">]</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// 谬构：下一语句不是同一迭代的一部分</span>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin"></table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|