117 lines
9.0 KiB
HTML
117 lines
9.0 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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<title>std::cin, std::wcin</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_cin 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>cin, <span style="font-size:0.7em; line-height:130%">std::</span>wcin</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-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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">extern</span> <a href="cpp-io-basic_istream.html"><span class="kw1727">std::<span class="me2">istream</span></span></a> cin<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_istream.html"><span class="kw1741">std::<span class="me2">wistream</span></span></a> wcin<span class="sy4">;</span></span></div>
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<p>全局对象 <code>std::cin</code> 和 <code>std::wcin</code> 控制来自实现定义类型（导出自 <span class="t-lc"><a href="cpp-io-basic_streambuf.html">std::streambuf</a></span> ）的流缓冲区的输入，与标准 C 输入流 <span class="t-lc"><a href="cpp-io-c.html">stdin</a></span> 关联。</p>
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<p>保证在首次构造 <span class="t-lc"><a href="cpp-io-ios_base-Init.html">std::ios_base::Init</a></span> 前或期间初始化这些对象，且它们可用于拥有<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>的静态对象的构造及析构函数（只要在定义该对象前包含 <code><iostream></code> ）。</p>
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<p>如果不使用 <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>， 则从多个线程访问这些对象，进行有格式和无格式输入是安全的。</p>
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<p>一旦构造 <code>std::cin</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">cin</span>.<span class="me1">tie</span><span class="br0">(</span><span class="br0">)</span></span></span> 就返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span><a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a></span></span> ，类似地 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">wcin</span>.<span class="me1">tie</span><span class="br0">(</span><span class="br0">)</span></span></span> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span><a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">wcout</span></span></a></span></span> 。这表示若有任何字符正在等待输出，则任何 <code>std::cin</code> 上的格式化输入操作会强制调用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a>.<span class="me1">flush</span><span class="br0">(</span><span class="br0">)</span></span></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“character”（ <a rel="nofollow" class="external text" href="http://www.stroustrup.com/bs_faq2.html#cout">stroustrup.com FAQ</a> ）； <code>cin</code> 表示“字符输入”而 <code>wcin</code> 表示“宽字符输入”。</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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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Enter n: "</span><span class="sy4">;</span> <span class="co1">// 不需要冲入</span>
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std<span class="sy4">::</span><span class="me2">cin</span> <span class="sy1">>></span> n<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">// static object</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="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"f.n is "</span> <span class="sy1"><<</span> f.<span class="me1">n</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">Enter n: 10
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f.n is 10</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-cout.html"><span class="t-lines"><span>cout</span><span>wcout</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 输出流 <span class="t-lc"><a href="cpp-io-c.html">stdout</a></span><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-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>
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<div class="visualClear"></div>
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