123 lines
12 KiB
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123 lines
12 KiB
HTML
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<title>std::basic_istream<CharT,Traits>::sync</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_istream_sync 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::basic_istream<CharT,Traits>::</span>sync</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-basic_istream.html">basic istream</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> sync<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>将输入缓冲区与关联数据源同步。</p>
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<p>表现为<a href="cpp-named_req-UnformattedInputFunction.html"><span style="font-style:italic">无格式输入函数</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UnformattedInputFunction)</span></a> ，除了不影响 <span class="t-lc"><a href="cpp-io-basic_istream-gcount.html">gcount()</a></span> 构造并检查 sentry 对象后，</p>
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<p>若 <span class="t-lc"><a href="cpp-io-basic_ios-rdbuf.html">rdbuf()</a></span> 为空指针，则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> 。</p>
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<p>否则调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">rdbuf<span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>pubsync<span class="br0">(</span><span class="br0">)</span></span></span> 。若该函数返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> ，则调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">setstate<span class="br0">(</span>badbit<span class="br0">)</span></span></span> 并返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> 。否则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 。</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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<p>（无）</p>
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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>成功时为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ，失败时或若流不支持此操作（无缓冲）则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>同 <span class="t-lc"><a href="cpp-io-basic_istream-readsome.html">readsome()</a></span> ，此函数是否对库提供的流做任何事是实现定义的。意图典型地是为了令下个读取操作拾取任何在流缓冲最后填充其获取区后，可能已对关联输入序列做出的更改。为达成之， <code>sync()</code> 可以清空获取区，或重填充它，或不做任何事。值得注意的例外是 Visual Studio ，其中此操作在以标准输入流调用时舍弃未处理的输出。</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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<p>演示以文件输入使用输入流 sync() ，在一些平台上实现。</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 <iostream></span>
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<span class="co2">#include <fstream></span>
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<span class="kw4">void</span> file_abc<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-basic_ofstream.html"><span class="kw1733">std::<span class="me2">ofstream</span></span></a> f<span class="br0">(</span><span class="st0">"test.txt"</span><span class="br0">)</span><span class="sy4">;</span>
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f <span class="sy1"><<</span> <span class="st0">"abc<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> file_123<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-basic_ofstream.html"><span class="kw1733">std::<span class="me2">ofstream</span></span></a> f<span class="br0">(</span><span class="st0">"test.txt"</span><span class="br0">)</span><span class="sy4">;</span>
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f <span class="sy1"><<</span> <span class="st0">"123<span class="es1">\n</span>"</span><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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file_abc<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 文件现在含 "abc"</span>
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<a href="cpp-io-basic_ifstream.html"><span class="kw1732">std::<span class="me2">ifstream</span></span></a> f<span class="br0">(</span><span class="st0">"test.txt"</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">"Reading from the file<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw4">char</span> c<span class="sy4">;</span>
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f <span class="sy1">>></span> c<span class="sy4">;</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> c<span class="sy4">;</span>
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file_123<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 文件现在含 "123"</span>
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f <span class="sy1">>></span> c<span class="sy4">;</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> c<span class="sy4">;</span>
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f <span class="sy1">>></span> c<span class="sy4">;</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> c <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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f.<span class="me1">close</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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file_abc<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 文件现在含 "abc"</span>
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f.<span class="me1">open</span><span class="br0">(</span><span class="st0">"test.txt"</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">"Reading from the file, with sync()<span class="es1">\n</span>"</span><span class="sy4">;</span>
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f <span class="sy1">>></span> c<span class="sy4">;</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> c<span class="sy4">;</span>
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file_123<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 文件现在含 "123"</span>
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f.<span class="me1">sync</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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f <span class="sy1">>></span> c<span class="sy4">;</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> c<span class="sy4">;</span>
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f <span class="sy1">>></span> c<span class="sy4">;</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> c <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>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">Reading from the file
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abc
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Reading from the file, with sync()
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a23</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_streambuf-pubsync.html"><span class="t-lines"><span>sync</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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</div>
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</td>
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<td>将缓冲与关联的字符序列同步<br />
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<span class="t-mark">(<code>std::basic_streambuf<CharT,Traits></code> 的虚受保护成员函数)</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-basic_ostream-flush.html"><span class="t-lines"><span>flush</span></span></a></div>
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</div>
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</td>
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<td>与底层存储设备同步<br />
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<span class="t-mark">(<code>std::basic_ostream<CharT,Traits></code> 的公开成员函数)</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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