217 lines
16 KiB
HTML
217 lines
16 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::basic_fstream<CharT,Traits>::basic_fstream</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_fstream_basic_fstream skin-cppreference2 action-view cpp-page-template cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::basic_fstream<CharT,Traits>::</span>basic_fstream</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_fstream.html">basic fstream</a></span></div>
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<div class="t-page-template" style="">
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<p></p>
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<div><span class="mw-geshi cpp source-cpp">basic_fstream<span class="br0">(</span><span class="br0">)</span><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="kw1">explicit</span> basic_fstream<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> filename,<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="sy1">=</span> ios_base<span class="sy4">::</span><span class="me2">in</span><span class="sy3">|</span>ios_base<span class="sy4">::</span><span class="me2">out</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> basic_fstream<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> filename,<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="sy1">=</span> ios_base<span class="sy4">::</span><span class="me2">in</span><span class="sy3">|</span>ios_base<span class="sy4">::</span><span class="me2">out</span> <span class="br0">)</span><span class="sy4">;</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>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> basic_fstream<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> filename,<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="sy1">=</span> ios_base<span class="sy4">::</span><span class="me2">in</span><span class="sy3">|</span>ios_base<span class="sy4">::</span><span class="me2">out</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 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"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span><br /></span>
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<p><span class="kw1">explicit</span> basic_fstream<span class="br0">(</span> <span class="kw4">const</span> T<span class="sy3">&</span> filename,<br /></p>
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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="sy1">=</span> ios_base<span class="sy4">::</span><span class="me2">in</span><span class="sy3">|</span>ios_base<span class="sy4">::</span><span class="me2">out</span> <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(5)</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-cxx11">
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<div><span class="mw-geshi cpp source-cpp">basic_fstream<span class="br0">(</span> basic_fstream<span class="sy3">&&</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(6)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp">basic_fstream<span class="br0">(</span> <span class="kw4">const</span> basic_fstream<span class="sy3">&</span> rhs<span class="br0">)</span> <span class="sy1">=</span> delete<span class="sy4">;</span></span></div>
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</td>
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<td>(7)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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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</tbody>
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<p>构造新的文件流。</p>
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<div class="t-li1"><span class="t-li">1)</span> 默认构造函数：构造不关联到文件的流：默认构造 <span class="t-lc"><a href="cpp-io-basic_filebuf.html">std::basic_filebuf</a></span> 并构造拥有指向此默认构造的 <span class="t-lc"><a href="cpp-io-basic_filebuf.html">std::basic_filebuf</a></span> 成员的基类。</div>
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<div class="t-li1"><span class="t-li">2-3)</span> 首先，进行同默认构造函数的步骤，然后通过调用 <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>open<span class="br0">(</span>filename, mode<span class="br0">)</span></span></span>（该调用效果上的细节见 <span class="t-lc"><a href="cpp-io-basic_filebuf-open.html">std::basic_filebuf::open</a></span> ）关联流与文件。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">open<span class="br0">(</span><span class="br0">)</span></span></span> 调用返回空指针，则设置 <span class="t-c"><span class="mw-geshi cpp source-cpp">setstate<span class="br0">(</span>failbit<span class="br0">)</span></span></span> 。<span class="t-rev-inl t-since-cxx17"><span>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">(3)</span> 。</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span></div>
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<div class="t-li1"><span class="t-li">4-5)</span> 同 <span class="t-c"><span class="mw-geshi cpp source-cpp">basic_fstream<span class="br0">(</span>filename.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span>, mode<span class="br0">)</span></span></span> 。 <span class="t-rev-inl t-since-cxx17"><span><span class="t-v">(5)</span> 仅若 <code>T</code> 为 <span class="t-lc"><a href="cpp-filesystem-path.html">std::filesystem::path</a></span> 才参与重载决议。</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span></div>
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<div class="t-li1"><span class="t-li">6)</span> 移动构造函数：首先，从 <code>other</code> 移动构造基类（这不影响 <code>rdbuf()</code> 指针），然后移动构造 <span class="t-lc"><a href="cpp-io-basic_filebuf.html">std::basic_filebuf</a></span> 成员，再调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">this<span class="sy2">-</span><span class="sy1">></span>set_rdbuf<span class="br0">(</span><span class="br0">)</span></span></span> 安装新的 <code>basic_filebuf</code> 为基类中的 <span class="t-c"><span class="mw-geshi cpp source-cpp">rdbuf<span class="br0">(</span><span class="br0">)</span></span></span> 指针。</div>
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<div class="t-li1"><span class="t-li">7)</span> 复制构造函数被删除：此类不可复制。</div>
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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>filename</td>
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<td>-</td>
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<td>要打开的文件名</td>
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</tr>
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<tr class="t-par">
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<td>mode</td>
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<td>-</td>
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<td>指定打开模式。可使用下列常量或它们之间的逐位或：
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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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<td>常量</td>
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<td>解释</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>app</tt></a></td>
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<td>每次写入前寻位到流结尾</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>binary</tt></a></td>
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<td>以<a href="cpp-io-c-FILE.html#.E4.BA.8C.E8.BF.9B.E5.88.B6.E4.B8.8E.E6.96.87.E6.9C.AC.E6.A8.A1.E5.BC.8F">二进制模式</a>打开</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>in</tt></a></td>
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<td>为读打开</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>out</tt></a></td>
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<td>为写打开</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>trunc</tt></a></td>
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<td>在打开时舍弃流的内容</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>ate</tt></a></td>
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<td>打开后立即寻位到流结尾</td>
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</tr>
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</table>
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</td>
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</tr>
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<tr class="t-par">
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<td>other</td>
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<td>-</td>
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<td>用作源的另一文件流</td>
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</tr>
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</table>
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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 t-example-std-cxx11">
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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 <fstream></span>
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<span class="co2">#include <utility></span>
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<span class="co2">#include <string></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-basic_fstream.html"><span class="kw1734">std::<span class="me2">fstream</span></span></a> f0<span class="sy4">;</span>
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<a href="cpp-io-basic_fstream.html"><span class="kw1734">std::<span class="me2">fstream</span></span></a> f1<span class="br0">(</span><span class="st0">"test.bin"</span>, std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">binary</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> name <span class="sy1">=</span> <span class="st0">"example.txt"</span><span class="sy4">;</span>
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<a href="cpp-io-basic_fstream.html"><span class="kw1734">std::<span class="me2">fstream</span></span></a> f2<span class="br0">(</span>name<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-basic_fstream.html"><span class="kw1734">std::<span class="me2">fstream</span></span></a> f3<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>f1<span class="br0">)</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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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3430">LWG 3430</a></td>
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<td>C++17</td>
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<td><span class="t-lc"><a href="cpp-filesystem-path.html">std::filesystem::path</a></span> 重载导致了不想要的转换</td>
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<td>使之为模板以避免</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_fstream-open.html"><span class="t-lines"><span>open</span></span></a></div>
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</div>
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</td>
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<td>打开文件，并将它与流关联<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-open.html"><span class="t-lines"><span>open</span></span></a></div>
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</div>
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</td>
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<td>打开文件并配置它为关联字符序列<br />
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<span class="t-mark">(<code>std::basic_filebuf<CharT,Traits></code> 的公开成员函数)</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_ios-set_rdbuf.html"><span class="t-lines"><span>set_rdbuf</span></span></a></div>
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</div>
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</td>
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<td>替换 <code>rdbuf</code> 而不清除其错误状态<br />
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<span class="t-mark">(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 t-dsc-member-nobold-div">
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<div><a href="cpp-io-basic_iostream-basic_iostream.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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<td>构造对象<br />
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<span class="t-mark">(<code>std::basic_iostream<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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</div>
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</body>
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</html>
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