186 lines
12 KiB
HTML
186 lines
12 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>return 语句</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_return skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading">return 语句</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-language.html">language</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<p>终止当前函数并返回指定值给调用方函数。</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><span class="t-spar">属性说明符序列</span><span class="t-mark">(可选)</span> <code><b>return</b></code> <span class="t-spar">表达式</span> <code><b>;</b></code></td>
|
|
<td>(1)</td>
|
|
<td class="t-sdsc-nopad"></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="10" class="t-sdsc-sep"></td>
|
|
</tr>
|
|
<tr class="t-sdsc">
|
|
<td><span class="t-spar">属性说明符序列</span><span class="t-mark">(可选)</span> <code><b>return</b></code> <code><b>;</b></code></td>
|
|
<td>(2)</td>
|
|
<td class="t-sdsc-nopad"></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="10" class="t-sdsc-sep"></td>
|
|
</tr>
|
|
</table>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td><span class="t-spar">表达式</span></td>
|
|
<td>-</td>
|
|
<td>用于初始化函数返回值的表达式</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td><span class="t-spar">属性说明符序列</span></td>
|
|
<td>-</td>
|
|
<td><span class="t-mark-rev t-since-c23">(C23)</span>可选的<a href="c-language-attributes.html">属性</a>列表，应用到 <code>return</code> 语句</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
|
|
<div class="t-li1"><span class="t-li">1)</span> 求值 <span class="t-spar">表达式</span> ，终止当前函数，并返回 <span class="t-spar">表达式</span> 的结果给调用方（返回值成为函数调用表达式的值）。仅对函数返回类型非 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span></span></span> 的情形合法。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 终止当前函数。仅对函数返回类型为 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span></span></span> 的情形合法。</div>
|
|
<p>若 <span class="t-spar">表达式</span> 的类型异于函数的返回类型，则如同赋值一般<a href="c-language-conversion.html">转换</a>其值为对象，对象类型为函数的返回类型，除了容许对象表示间的重叠：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="kw1">struct</span> s <span class="br0">{</span> <span class="kw4">double</span> i<span class="sy4">;</span> <span class="br0">}</span> f<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 函数返回 struct s</span>
|
|
<span class="kw1">union</span> <span class="br0">{</span> <span class="kw1">struct</span> <span class="br0">{</span> <span class="kw4">int</span> f1<span class="sy4">;</span> <span class="kw1">struct</span> s f2<span class="sy4">;</span> <span class="br0">}</span> u1<span class="sy4">;</span>
|
|
<span class="kw1">struct</span> <span class="br0">{</span> <span class="kw1">struct</span> s f3<span class="sy4">;</span> <span class="kw4">int</span> f4<span class="sy4">;</span> <span class="br0">}</span> u2<span class="sy4">;</span> <span class="br0">}</span> g<span class="sy4">;</span>
|
|
<span class="kw1">struct</span> s f<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">return</span> g.<span class="me1">u1</span>.<span class="me1">f2</span><span class="sy4">;</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="co1">// g.u2.f3 = g.u1.f2; // 未定义行为（赋值中重叠）</span>
|
|
g.<span class="me1">u2</span>.<span class="me1">f3</span> <span class="sy1">=</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 良好定义</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>若返回类型是实浮点类型，则结果可能拥有比新类型所隐含者<a href="c-types-limits-FLT_EVAL_METHOD.html">更大的范围和精度</a>的表示。</p>
|
|
<p>抵达返回 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span></span></span> 的函数的末尾等价于 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw1">return</span><span class="sy4">;</span></span></span>。若函数结果用于表达式，则抵达任何其他返回值的函数的结尾为未定义行为（允许舍弃这种返回值）。对于 <code>main</code>，见 <a href="c-language-main_function.html"><code>main</code> 函数</a>。</p>
|
|
<table class="t-rev-begin">
|
|
<tr class="t-rev t-since-c11">
|
|
<td>
|
|
<p>在<a href="c-language-_Noreturn.html">不返回函数</a>中执行 <code>return</code> 语句是未定义行为。</p>
|
|
</td>
|
|
<td><span class="t-mark-rev t-since-c11">(C11 起)</span></td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E5.85.B3.E9.94.AE.E8.AF.8D">关键词</span></h3>
|
|
<p><a href="c-keyword-return.html"><tt>return</tt></a></p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
|
|
<tr>
|
|
<td class="mbox-empty-cell"></td>
|
|
<td class="mbox-text" style="">本节未完成<br />
|
|
原因：改进</td>
|
|
</tr>
|
|
</table>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="co2">#include <stdio.h></span>
|
|
|
|
<span class="kw4">void</span> fa<span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">if</span> <span class="br0">(</span>i <span class="sy1">==</span> <span class="nu0">2</span><span class="br0">)</span>
|
|
<span class="kw1">return</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"fa(): %d<span class="es1">\n</span>"</span>, i<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span> <span class="co1">// 隐含return;</span>
|
|
|
|
<span class="kw4">int</span> fb<span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">if</span> <span class="br0">(</span>i <span class="sy1">></span> <span class="nu0">4</span><span class="br0">)</span>
|
|
<span class="kw1">return</span> <span class="nu0">4</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"fb(): %d<span class="es1">\n</span>"</span>, i<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">return</span> <span class="nu0">2</span><span class="sy4">;</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>
|
|
fa<span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span><span class="sy4">;</span>
|
|
fa<span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">int</span> i <span class="sy1">=</span> fb<span class="br0">(</span><span class="nu0">5</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 返回值 4 用于初始化 i</span>
|
|
i <span class="sy1">=</span> fb<span class="br0">(</span>i<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 返回值 2 用作赋值的右运算数</span>
|
|
<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"main(): %d<span class="es1">\n</span>"</span>, i<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">fa(): 1
|
|
fb(): 4
|
|
main(): 2</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
|
|
<div class="t-ref-std-17">
|
|
<ul>
|
|
<li>C17 标准（ISO/IEC 9899:2018）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.8.6.4 The return statement (p: 111-112)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<div class="t-ref-std-11">
|
|
<ul>
|
|
<li>C11 标准（ISO/IEC 9899:2011）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.8.6.4 The return statement (p: 154)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<div class="t-ref-std-c99">
|
|
<ul>
|
|
<li>C99 标准（ISO/IEC 9899:1999）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>6.8.6.4 The return statement (p: 139)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<div class="t-ref-std-c89">
|
|
<ul>
|
|
<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>3.6.6.4 The return statement</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</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>
|