90 lines
7.5 KiB
HTML
90 lines
7.5 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>override 说明符(C++11 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-cpp_language_override skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading">override 说明符<span class="t-mark-rev t-since-cxx11">(C++11 起)</span></h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-language.html">language</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<p>指定一个<a href="cpp-language-virtual.html">虚函数</a>覆盖另一个虚函数。</p>
|
|
<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
|
|
<p>如果使用标识符 <code>override</code>，那么它紧随成员函数声明或类定义内的成员函数定义语法中的<a href="cpp-language-function.html">声明符</a>之后出现。</p>
|
|
<table class="t-sdsc-begin">
|
|
<tr>
|
|
<td colspan="10" class="t-sdsc-sep"></td>
|
|
</tr>
|
|
<tr class="t-sdsc">
|
|
<td><span class="t-spar">声明符</span> <span class="t-spar">虚说明符序列</span><span class="t-mark">(可选)</span> <span class="t-spar">纯说明符</span><span class="t-mark">(可选)</span></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">声明符</span> <span class="t-spar">虚说明符序列</span><span class="t-mark">(可选)</span> <span class="t-spar">函数体</span></td>
|
|
<td>(2)</td>
|
|
<td class="t-sdsc-nopad"></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="10" class="t-sdsc-sep"></td>
|
|
</tr>
|
|
</table>
|
|
<div class="t-li1"><span class="t-li">1)</span> 在成员函数声明中，<code>override</code> 可以在紧随声明符之后并在 <a href="cpp-language-abstract_class.html"><span class="t-spar">纯说明符</span></a> 之前（如有使用）的 <span class="t-spar">虚说明符序列</span> 中出现。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 在类定义内成员函数定义中，<code>override</code> 可以在紧随声明符之后并紧接 <span class="t-spar">函数体</span> 之前的 <span class="t-spar">虚说明符序列</span> 中出现。</div>
|
|
<p>两种情况中，如果使用 <span class="t-spar">虚说明符序列</span> ，那么它必须是 <code>override</code>、<a href="cpp-language-final.html"><code>final</code></a>、<code>final override</code> 或 <code>override final</code> 之一。</p>
|
|
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
|
|
<p>在成员函数的声明或定义中，<code>override</code> 说明符确保该函数为虚函数并覆盖某个基类中的虚函数。如果不是这样，那么程序为谬构（生成编译错误）。</p>
|
|
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">override</span></span> 是在成员函数声明符之后使用时拥有特殊含义的标识符：其他情况下它不是保留的关键词。</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="cpp source-cpp">
|
|
<pre class="de1"><span class="kw1">struct</span> A
|
|
<span class="br0">{</span>
|
|
<span class="kw1">virtual</span> <span class="kw4">void</span> foo<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">void</span> bar<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="kw1">struct</span> B <span class="sy4">:</span> A
|
|
<span class="br0">{</span>
|
|
<span class="kw4">void</span> foo<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> override<span class="sy4">;</span> <span class="co1">// 错误：B::foo 不覆盖 A::foo</span>
|
|
<span class="co1">// （签名不匹配）</span>
|
|
<span class="kw4">void</span> foo<span class="br0">(</span><span class="br0">)</span> override<span class="sy4">;</span> <span class="co1">// OK：B::foo 覆盖 A::foo</span>
|
|
<span class="kw4">void</span> bar<span class="br0">(</span><span class="br0">)</span> override<span class="sy4">;</span> <span class="co1">// 错误：A::bar 非虚</span>
|
|
<span class="br0">}</span><span class="sy4">;</span></pre></div>
|
|
</div>
|
|
<p>可能的输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">main.cpp:9:10: 错误：'void B::foo() const' 标记为 'override'，但没有覆盖
|
|
9 | void foo() const override; // 错误：B::foo 不覆盖 A::foo
|
|
| ^~~
|
|
main.cpp:12:10: 错误：'void B::bar()' 标记为 'override'，但没有覆盖
|
|
12 | void bar() override; // Error: A::bar 非虚
|
|
| ^~~</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">
|
|
<tr class="t-dsc">
|
|
<td><a href="cpp-language-final.html"><code>final</code> 说明符</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
|
|
<td>声明不能被覆盖的方法</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|