203 lines
14 KiB
HTML
203 lines
14 KiB
HTML
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<title>std::basic_filebuf<CharT,Traits>::open</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_filebuf_open 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_filebuf<CharT,Traits>::</span>open</h1>
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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_filebuf.html">basic filebuf</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-io-basic_filebuf.html"><span class="kw1667">std::<span class="me2">basic_filebuf</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy2">*</span> open<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> s,<br />
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<a href="cpp-io-ios_base-openmode.html"><span class="kw1671">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">openmode</span></span></a> mode <span class="br0">)</span></span></div>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-io-basic_filebuf.html"><span class="kw1667">std::<span class="me2">basic_filebuf</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy2">*</span> open<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy3">&</span> str,<br />
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<a href="cpp-io-ios_base-openmode.html"><span class="kw1671">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">openmode</span></span></a> mode <span class="br0">)</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-io-basic_filebuf.html"><span class="kw1667">std::<span class="me2">basic_filebuf</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy2">*</span> open<span class="br0">(</span> <span class="kw4">const</span> <a href="cpp-filesystem-path.html"><span class="kw2199">std::<span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">path</span></span></a><span class="sy3">&</span> p,<br />
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<a href="cpp-io-ios_base-openmode.html"><span class="kw1671">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">openmode</span></span></a> mode <span class="br0">)</span></span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<tr class="t-dcl t-since-cxx17">
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-io-basic_filebuf.html"><span class="kw1667">std::<span class="me2">basic_filebuf</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy2">*</span> open<span class="br0">(</span> <span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">path</span><span class="sy4">::</span><span class="me2">value_type</span><span class="sy2">*</span> s,<br />
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<a href="cpp-io-ios_base-openmode.html"><span class="kw1671">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">openmode</span></span></a> mode <span class="br0">)</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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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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<p>打开拥有给定名称（ <span class="t-c"><span class="mw-geshi cpp source-cpp">s</span></span> <span class="t-rev-inl t-since-cxx17"><span>、 <span class="t-c"><span class="mw-geshi cpp source-cpp">p.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span></span></span></span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span></span></span> ，取决于重载）的文件。</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx17">
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<td>
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<p>仅若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">filesystem</span><span class="sy4">::</span><span class="me2">path</span><span class="sy4">::</span><span class="me2">value_type</span></span></span> 非 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span> 才提供重载 <span class="t-v">(4)</span> 。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>如同通过以按下列方式确定的第二参数 (<code>mode</code>) 调用 <span class="t-lc"><a href="cpp-io-c-fopen.html">std::fopen</a></span> 打开文件：</p>
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<table class="wikitable">
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<th>mode</th>
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<th>openmode & ~ate</th>
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<th>若文件已存在的动作</th>
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<th>若文件不存在的动作</th>
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</tr>
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<tr>
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<td>"r"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">in</span></span></td>
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<td>从头读取</td>
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<td>打开失败</td>
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</tr>
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<tr>
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<td>"w"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">out</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">out<span class="sy3">|</span>trunc</span></span></td>
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<td>销毁内容</td>
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<td>创建新文件</td>
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</tr>
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<tr>
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<td>"a"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">app</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">out<span class="sy3">|</span>app</span></span></td>
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<td>后附到文件</td>
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<td>创建新文件</td>
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</tr>
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<tr>
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<td>"r+"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">out<span class="sy3">|</span>in</span></span></td>
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<td>从头读取</td>
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<td>错误</td>
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</tr>
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<tr>
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<td>"w+"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">out<span class="sy3">|</span>in<span class="sy3">|</span>trunc</span></span></td>
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<td>销毁内容</td>
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<td>创建新文件</td>
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</tr>
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<tr>
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<td>"a+"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">out<span class="sy3">|</span>in<span class="sy3">|</span>app</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">in<span class="sy3">|</span>app</span></span></td>
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<td>写入到结尾</td>
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<td>创建新文件</td>
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</tr>
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<tr>
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<td>"rb"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>in</span></span></td>
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<td>从头读取</td>
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<td>打开失败</td>
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</tr>
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<tr>
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<td>"wb"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>out</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>out<span class="sy3">|</span>trunc</span></span></td>
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<td>销毁内容</td>
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<td>创建新文件</td>
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</tr>
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<tr>
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<td>"ab"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>app</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>out<span class="sy3">|</span>app</span></span></td>
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<td>写入结尾</td>
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<td>创建新文件</td>
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</tr>
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<tr>
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<td>"r+b"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>out<span class="sy3">|</span>in</span></span></td>
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<td>从头读取</td>
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<td>错误</td>
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</tr>
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<tr>
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<td>"w+b"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>out<span class="sy3">|</span>in<span class="sy3">|</span>trunc</span></span></td>
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<td>销毁内容</td>
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<td>创建新文件</td>
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</tr>
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<tr>
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<td>"a+b"</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>out<span class="sy3">|</span>in<span class="sy3">|</span>app</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">binary<span class="sy3">|</span>in<span class="sy3">|</span>app</span></span></td>
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<td>写入到结尾</td>
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<td>创建新文件</td>
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</tr>
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</table>
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<p>若 <code>openmode</code> 不是列出的模式之一，则 <code>open()</code> 失败。</p>
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<p>若打开操作成功且 <span class="t-c"><span class="mw-geshi cpp source-cpp">openmode <span class="sy3">&</span> <a href="cpp-io-ios_base-openmode.html"><span class="kw1677">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">ate</span></span></a> <span class="sy3">!</span><span class="sy1">=</span> <span class="nu0">0</span></span></span> （设置了 <code>ate</code> 位），则重寻位文件位置到文件尾，如同用调用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c-fseek.html"><span class="kw1867">std::<span class="me2">fseek</span></span></a><span class="br0">(</span>file, <span class="nu0">0</span>, <a href="cpp-io-c.html"><span class="kw1891">SEEK_END</span></a><span class="br0">)</span></span></span> ，其中 <code>file</code> 是调用 <code>fopen</code> 返回的指针。若寻位失败，则调用 <span class="t-lc"><a href="cpp-io-basic_filebuf-close.html">close()</a></span> 并返回空指针以指示失败。</p>
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<p>若关联文件已打开，则立即返回空指针。</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>s, str, p</td>
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<td>-</td>
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<td>要打开的文件名； <code>s</code> 必须指向空终止字符串</td>
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</tr>
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<tr class="t-par">
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<td>openmode</td>
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<td>-</td>
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<td>文件打开模式， <span class="t-lc"><a href="cpp-io-ios_base.html">std::ios_base</a></span> 模式的二进制或</td>
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</tr>
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</table>
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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">this</span></span> ，失败时为空指针。</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>常由 <span class="t-lc"><a href="cpp-io-basic_fstream.html">std::basic_fstream</a></span> 的构造函数或 <code>open()</code> 成员函数调用 <code>open()</code> 。</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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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<tr>
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<td class="mbox-empty-cell"></td>
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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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</tr>
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</table>
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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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<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_filebuf-is_open.html"><span class="t-lines"><span>is_open</span></span></a></div>
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</div>
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</td>
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<td>检查关联文件是否打开<br />
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<span class="t-mark">(公开成员函数)</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_filebuf-close.html"><span class="t-lines"><span>close</span></span></a></div>
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</div>
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</td>
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<td>冲入放置区缓冲区并关闭关联的文件<br />
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<span class="t-mark">(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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</body>
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