97 lines
5.3 KiB
HTML
97 lines
5.3 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>命名空间别名</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_namespace_alias 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">命名空间别名</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>命名空间别名允许程序员定义命名空间的另一个名字。</p>
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<p>它们常用作长的或嵌套过深的命名空间的简便使用方式。</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>
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<tr class="t-sdsc">
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<td><code><b>namespace</b></code> <span class="t-spar">别名</span> = <span class="t-spar">命名空间名</span><code><b>;</b></code></td>
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<td>(1)</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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<tr class="t-sdsc">
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<td><code><b>namespace</b></code> <span class="t-spar">别名</span> = <code><b>::</b></code><span class="t-spar">命名空间名</span><code><b>;</b></code></td>
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<td>(2)</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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<tr class="t-sdsc">
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<td><code><b>namespace</b></code> <span class="t-spar">别名</span> = <span class="t-spar">嵌套名</span><code><b>::</b></code><span class="t-spar">命名空间名</span><code><b>;</b></code></td>
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<td>(3)</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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<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
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<p>新别名 <span class="t-spar">别名</span> 提供另一种访问 <span class="t-spar">命名空间名</span> 的方法。</p>
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<p><span class="t-spar">别名</span> 必须是先前未使用过的名称。<span class="t-spar">别名</span> 在引入它的作用域的期间内有效。</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="kw1">namespace</span> foo <span class="br0">{</span>
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<span class="kw1">namespace</span> bar <span class="br0">{</span>
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<span class="kw1">namespace</span> baz <span class="br0">{</span>
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<span class="kw4">int</span> qux <span class="sy1">=</span> <span class="nu0">42</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>
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<span class="kw1">namespace</span> fbz <span class="sy1">=</span> foo<span class="sy4">::</span><span class="me2">bar</span><span class="sy4">::</span><span class="me2">baz</span><span class="sy4">;</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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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> fbz<span class="sy4">::</span><span class="me2">qux</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</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>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">42</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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<tr class="t-dsc">
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<td><a href="cpp-language-namespace.html">命名空间声明</a></td>
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<td>标识命名空间</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-language-type_alias.html">类型别名声明</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
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<td>创建类型的同义词</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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