115 lines
9.4 KiB
HTML
115 lines
9.4 KiB
HTML
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<title>std::ios_base::sync_with_stdio</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_ios_base_sync_with_stdio 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::ios_base::</span>sync_with_stdio</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-ios_base.html">ios base</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">static</span> <span class="kw4">bool</span> sync_with_stdio<span class="br0">(</span> <span class="kw4">bool</span> sync <span class="sy1">=</span> <span class="kw2">true</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td></td>
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<p>设置标准 C++ 流是否与标准 C 流在每次输入/输出操作后同步。</p>
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<p>标准 C++ 流为下列者： <span class="t-lc"><a href="cpp-io-cin.html">std::cin</a></span> 、 <span class="t-lc"><a href="cpp-io-cout.html">std::cout</a></span> 、 <span class="t-lc"><a href="cpp-io-cerr.html">std::cerr</a></span> 、 <span class="t-lc"><a href="cpp-io-clog.html">std::clog</a></span> 、 <span class="t-lc"><a href="cpp-io-cin.html">std::wcin</a></span> 、 <span class="t-lc"><a href="cpp-io-cout.html">std::wcout</a></span> 、 <span class="t-lc"><a href="cpp-io-cerr.html">std::wcerr</a></span> 和 <span class="t-lc"><a href="cpp-io-clog.html">std::wclog</a></span> 。</p>
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<p>标准 C 流为下列者： <span class="t-lc"><a href="cpp-io-c.html">stdin</a></span> 、 <span class="t-lc"><a href="cpp-io-c.html">stdout</a></span> 和 <span class="t-lc"><a href="cpp-io-c.html">stderr</a></span> 。</p>
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<p>对于与 C 流 <code>f</code> 同步的标准流 <code>str</code> ，下列函数对拥有等同的效果：</p>
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<div class="t-li1"><span class="t-li">1)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c-fputc.html"><span class="kw1824">std::<span class="me2">fputc</span></span></a><span class="br0">(</span>f, c<span class="br0">)</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>sputc<span class="br0">(</span>c<span class="br0">)</span></span></span></div>
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<div class="t-li1"><span class="t-li">2)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c-fgetc.html"><span class="kw1821">std::<span class="me2">fgetc</span></span></a><span class="br0">(</span>f<span class="br0">)</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>sbumpc<span class="br0">(</span><span class="br0">)</span></span></span></div>
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<div class="t-li1"><span class="t-li">3)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c-ungetc.html"><span class="kw1831">std::<span class="me2">ungetc</span></span></a><span class="br0">(</span>c, f<span class="br0">)</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>sputbackc<span class="br0">(</span>c<span class="br0">)</span></span></span></div>
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<p>实践中，这表示同步的 C++ 流为无缓冲，而每次 C++ 流上的 I/O 都立即应用到对应 C 流的缓冲区。这使得能自由地混合 C++ 与 C I/O 。</p>
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<p>另外，同步的 C++ 流保证为线程安全（从多个线程输出的单独字符可能交错，但无数据竞争）。</p>
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<p>若关闭同步，则允许 C++ 标准流独立地缓冲其 I/O ，可认为这在某些情况下更快。</p>
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<p>所有八个标准 C++ 流默认与其相应的 C 流同步。</p>
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<p>若在标准流上已出现 I/O 后调用此函数，则行为是实现定义的：有的实现无效果，有的实现销毁读取缓冲区。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>sync</td>
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<td>-</td>
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<td>新的同步设置</td>
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</tr>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>调用函数前的同步状态</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 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="co2">#include <cstdio></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">ios</span><span class="sy4">::</span><span class="me2">sync_with_stdio</span><span class="br0">(</span><span class="kw2">false</span><span class="br0">)</span><span class="sy4">;</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> <span class="st0">"a<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<a href="cpp-io-c-fprintf.html"><span class="kw1845">std::<span class="me2">printf</span></span></a><span class="br0">(</span><span class="st0">"b<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</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> <span class="st0">"c<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>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">b
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a
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c</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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<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-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 class="t-dsc">
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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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</table>
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</div>
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<div class="visualClear"></div>
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