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<title>std::basic_fstream&lt;CharT,Traits&gt;::is_open</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::basic_fstream&lt;CharT,Traits&gt;::</span>is_open</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-io.html">io</a>&lrm; | <a href="cpp-io-basic_fstream.html">basic fstream</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> is_open<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 &#21069;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> is_open<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 &#36215;)</span></td>
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<p>&#26816;&#26597;&#25991;&#20214;&#27969;&#26159;&#21542;&#26377;&#20851;&#32852;&#25991;&#20214;&#12290;</p>
<p>&#31561;&#25928;&#22320;&#35843;&#29992; <a href="cpp-io-basic_filebuf-is_open.html"><tt>rdbuf()-&gt;is_open()</tt></a> &#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
<p>&#65288;&#26080;&#65289;</p>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p>&#33509;&#25991;&#20214;&#27969;&#26377;&#20851;&#32852;&#25991;&#20214;&#65292;&#21017;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#65292;&#21542;&#21017;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> &#12290;</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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<pre class="de1"><span class="co2">#include &lt;string&gt;</span>
<span class="co2">#include &lt;fstream&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> filename <span class="sy1">=</span> <span class="st0">&quot;some_file&quot;</span><span class="sy4">;</span>
<a href="cpp-io-basic_fstream.html"><span class="kw1734">std::<span class="me2">fstream</span></span></a> fs<span class="br0">(</span>filename, std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">in</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;fs.is_open() = &quot;</span> <span class="sy1">&lt;&lt;</span> fs.<span class="me1">is_open</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="kw1">if</span><span class="br0">(</span><span class="sy3">!</span>fs.<span class="me1">is_open</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>
<span class="br0">{</span>
fs.<span class="me1">clear</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
fs.<span class="me1">open</span><span class="br0">(</span>filename, std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">out</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;fs.is_open() = &quot;</span> <span class="sy1">&lt;&lt;</span> fs.<span class="me1">is_open</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span></pre></div>
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<p>&#21487;&#33021;&#30340;&#36755;&#20986;&#65306;</p>
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<pre class="de1">fs.is_open() = false
fs.is_open() = true</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
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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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<td>&#25171;&#24320;&#25991;&#20214;&#65292;&#24182;&#23558;&#23427;&#19982;&#27969;&#20851;&#32852;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div><a href="cpp-io-basic_fstream-close.html"><span class="t-lines"><span>close</span></span></a></div>
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<td>&#20851;&#38381;&#20851;&#32852;&#25991;&#20214;<br />
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