130 lines
10 KiB
HTML
130 lines
10 KiB
HTML
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<title>std::cout, std::wcout</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_cout skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>cout, <span style="font-size:0.7em; line-height:130%">std::</span>wcout</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-io.html">io</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-iostream.html"><iostream></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">extern</span> <a href="cpp-io-basic_ostream.html"><span class="kw1729">std::<span class="me2">ostream</span></span></a> cout<span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">extern</span> <a href="cpp-io-basic_ostream.html"><span class="kw1743">std::<span class="me2">wostream</span></span></a> wcout<span class="sy4">;</span></span></div>
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<p>全局对象 <code>std::cout</code> 和 <code>std::wcout</code> 控制到实现定义类型流缓冲（导出自 <span class="t-lc"><a href="cpp-io-basic_streambuf.html">std::streambuf</a></span> ）的输出，它与标准 C 输出流 <span class="t-lc"><a href="cpp-io-c.html">stdout</a></span> 关联。</p>
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<p>保证这些对象在首次构造 <span class="t-lc"><a href="cpp-io-ios_base-Init.html">std::ios_base::Init</a></span> 类型对象期间或之前初始化，并可用于拥有<a href="cpp-language-initialization.html#.E9.9D.9E.E5.B1.80.E9.83.A8.E5.8F.98.E9.87.8F">有序初始化</a>的静态对象的构造函数和析构函数（只要在定义对象前包含 <code><iostream></code> ）。</p>
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<p>除非发出 <span class="t-c"><span class="mw-geshi cpp source-cpp">sync_with_stdio<span class="br0">(</span><span class="kw2">false</span><span class="br0">)</span></span></span> ，否则从多个线程为有格式和无格式输出同时访问这些对象是安全的。</p>
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<p>一旦初始化，则 <code>std::cout</code> 被 <span class="t-c"><span class="mw-geshi cpp source-cpp">tie<span class="br0">(</span><span class="br0">)</span></span></span> 到 <span class="t-lc"><a href="cpp-io-cin.html">std::cin</a></span> 而 <code>std::wcout</code> 被 tie() 到 <span class="t-lc"><a href="cpp-io-cin.html">std::wcin</a></span> ，这表示任何 <span class="t-lc"><a href="cpp-io-cin.html">std::cin</a></span> 上的输入操作执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">cout</span>.<span class="me1">flush</span><span class="br0">(</span><span class="br0">)</span></span></span> （通过 <span class="t-lc"><a href="cpp-io-basic_istream-sentry.html">std::basic_istream::sentry</a></span> 构造函数）。</p>
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<p>一旦初始化，则 <code>std::cout</code> 亦被 <span class="t-c"><span class="mw-geshi cpp source-cpp">tie<span class="br0">(</span><span class="br0">)</span></span></span> 到 <span class="t-lc"><a href="cpp-io-cerr.html">std::cerr</a></span> 而 <code>std::wcout</code> 被 tie() 到 <span class="t-lc"><a href="cpp-io-cerr.html">std::wcerr</a></span> ，这表示任何 <span class="t-lc"><a href="cpp-io-cerr.html">std::cerr</a></span> 上的输入操作执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">cout</span>.<span class="me1">flush</span><span class="br0">(</span><span class="br0">)</span></span></span> （通过 <span class="t-lc"><a href="cpp-io-basic_istream-sentry.html">std::basic_istream::sentry</a></span> 构造函数）。<span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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>名称中的 'c' 指代“字符”（ <a rel="nofollow" class="external text" href="http://www.stroustrup.com/bs_faq2.html#cout">stroustrup.com FAQ</a> ）； <code>cout</code> 表示“字符输出”而 <code>wcout</code> 表示“宽字符输出”。</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">struct</span> Foo <span class="br0">{</span>
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<span class="kw4">int</span> n<span class="sy4">;</span>
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Foo<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">cout</span> <span class="sy1"><<</span> <span class="st0">"static constructor<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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~Foo<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">cout</span> <span class="sy1"><<</span> <span class="st0">"static destructor<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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Foo f<span class="sy4">;</span> <span class="co1">// 静态对象</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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std<span class="sy4">::</span><span class="me2">cout</span> <span class="sy1"><<</span> <span class="st0">"main function<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">static constructor
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main function
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static destructor</pre></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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<div class="t-dsc-member-div">
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<div><a href="cpp-io-ios_base-Init.html"><span class="t-lines"><span>Init</span></span></a></div>
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</div>
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</td>
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<td>初始化标准流对象<br />
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<span class="t-mark">(<code>std::ios_base</code> 的公开成员类)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-cerr.html"><span class="t-lines"><span>cerr</span><span>wcerr</span></span></a></div>
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</div>
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</td>
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<td>写入到标准 C 错误流 <span class="t-lc"><a href="cpp-io-c.html">stderr</a></span>， 无缓冲<br />
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<span class="t-mark">(全局对象)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-clog.html"><span class="t-lines"><span>clog</span><span>wclog</span></span></a></div>
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</div>
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</td>
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<td>写入到标准 C 错误流 <span class="t-lc"><a href="cpp-io-c.html">stderr</a></span><br />
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<span class="t-mark">(全局对象)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-c-std_streams.html"><span class="t-lines"><span>stdin</span><span>stdout</span><span>stderr</span></span></a></div>
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</div>
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</td>
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<td>与输入流关联到 <span class="t-c"><span class="mw-geshi cpp source-cpp">FILE<span class="sy2">*</span></span></span> 类型表达式<br />
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与输出流关联的 <span class="t-c"><span class="mw-geshi cpp source-cpp">FILE<span class="sy2">*</span></span></span> 类型表达式<br />
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与错误输出流关联的 <span class="t-c"><span class="mw-geshi cpp source-cpp">FILE<span class="sy2">*</span></span></span> 类型表达式<br />
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<span class="t-mark">(宏常量)</span></td>
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<div class="visualClear"></div>
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