143 lines
9.5 KiB
HTML
143 lines
9.5 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>stdin, stdout, stderr</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_io_c_std_streams 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">stdin, stdout, stderr</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>‎ | <a href="cpp-io-c.html">c</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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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-cstdio.html"><cstdio></a></code></div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="co2">#define stdin /* implementation-defined */</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="co2">#define stdout /* implementation-defined */</span></span></div>
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</td>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="co2">#define stderr /* implementation-defined */</span></span></div>
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</td>
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<td>(3)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>预定义三个文本流。这些流在程序启动时隐式打开，且为无面向。</p>
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<div class="t-li1"><span class="t-li">1)</span> 与<i>标准输入</i>流关联，用于读取约定的输入。程序启动时，该流为完全缓冲当且仅当能确定流不引用交互式设备。</div>
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<div class="t-li1"><span class="t-li">2)</span> 与<i>标准输出</i>流关联，用于写入约定的输出。程序启动时，该流为完全缓冲当且仅当能确定流不引用交互式设备。</div>
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<div class="t-li1"><span class="t-li">3)</span> 与<i>标准错误</i>流关联，用于写入诊断输出。程序启动时，该流不为完全缓冲。</div>
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<p>何者组成交互式设备是实现定义的。</p>
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<p>这些宏展开成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c.html"><span class="kw1877">std::<span class="me2">FILE</span></span></a><span class="sy2">*</span></span></span> 类型表达式。</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>尽管 POSIX 不强制， UNIX 约定是 <code>stdin</code> 与 <code>stdout</code> 若与终端关联则为行缓冲，而 <code>stderr</code> 为无缓冲。</p>
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<p>这些宏可能展开成可修改左值。若修改任何这些 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c.html"><span class="kw1877">std::<span class="me2">FILE</span></span></a><span class="sy2">*</span></span></span> 左值，则对应的流上的后续操作导致未指明或未定义行为。</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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<p>此示例展示等价于 <span class="t-lc"><a href="cpp-io-c-fprintf.html">std::printf</a></span> 的函数。</p>
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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 <stdarg.h></span>
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<span class="co2">#include <stdio.h></span>
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<span class="kw4">int</span> my_printf<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span> fmt, ...<span class="br0">)</span>
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<span class="br0">{</span>
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std<span class="sy4">::</span><span class="kw4">va_list</span> vl<span class="sy4">;</span>
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<a href="cpp-utility-variadic-va_start.html"><span class="kw961">va_start</span></a><span class="br0">(</span>vl, fmt<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> ret <span class="sy1">=</span> <a href="cpp-io-c-vfprintf.html"><span class="kw1850">std::<span class="me2">vfprintf</span></span></a><span class="br0">(</span><span class="kw2">stdout</span>, fmt, vl<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-utility-variadic-va_end.html"><span class="kw964">va_end</span></a><span class="br0">(</span>vl<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> ret<span class="sy4">;</span>
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<span class="br0">}</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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my_printf<span class="br0">(</span><span class="st0">"Rounding:<span class="es1">\t</span>%f %.0f %.32f<span class="es1">\n</span>"</span>, <span class="nu16">1.5</span>, <span class="nu16">1.5</span>, <span class="nu16">1.3</span><span class="br0">)</span><span class="sy4">;</span>
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my_printf<span class="br0">(</span><span class="st0">"Padding:<span class="es1">\t</span>%05.2f %.2f %5.2f<span class="es1">\n</span>"</span>, <span class="nu16">1.5</span>, <span class="nu16">1.5</span>, <span class="nu16">1.5</span><span class="br0">)</span><span class="sy4">;</span>
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my_printf<span class="br0">(</span><span class="st0">"Scientific:<span class="es1">\t</span>%E %e<span class="es1">\n</span>"</span>, <span class="nu16">1.5</span>, <span class="nu16">1.5</span><span class="br0">)</span><span class="sy4">;</span>
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my_printf<span class="br0">(</span><span class="st0">"Hexadecimal:<span class="es1">\t</span>%a %A<span class="es1">\n</span>"</span>, <span class="nu16">1.5</span>, <span class="nu16">1.5</span><span class="br0">)</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>可能的输出：</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">Rounding: 1.500000 2 1.30000000000000004440892098500626
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Padding: 01.50 1.50 1.50
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Scientific: 1.500000E+00 1.500000e+00
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Hexadecimal: 0x1.8p+0 0X1.8P+0</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-cin.html"><span class="t-lines"><span>cin</span><span>wcin</span></span></a></div>
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</div>
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</td>
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<td>从标准 C 输入流 <span class="t-lc"><a href="cpp-io-c.html">stdin</a></span> 中读取<br />
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<span class="t-mark">(全局对象)</span></td>
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</tr>
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<tr class="t-dsc">
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<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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</tr>
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<tr class="t-dsc">
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<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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</tr>
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<tr class="t-dsc">
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<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>
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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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