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<title>std::basic_ios&lt;CharT,Traits&gt;::operator bool</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::basic_ios&lt;CharT,Traits&gt;::</span>operator bool</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_ios.html">basic ios</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">operator <span class="kw4">void</span><span class="sy2">*</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
<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="kw1">explicit</span> operator <span class="kw4">bool</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
<td><span class="t-mark-rev t-since-cxx11">(C++11 &#36215;)</span></td>
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<p>&#26816;&#26597;&#27969;&#26159;&#21542;&#26080;&#38169;&#35823;&#12290;</p>
<div class="t-li1"><span class="t-li">1)</span> &#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">fail<span class="br0">(</span><span class="br0">)</span></span></span> &#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#21017;&#36820;&#22238;&#31354;&#25351;&#38024;&#65292;&#21542;&#21017;&#36820;&#22238;&#38750;&#31354;&#25351;&#38024;&#12290;&#27492;&#25351;&#38024;&#21487;&#38544;&#24335;&#36716;&#25442;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> &#65292;&#24182;&#21487;&#29992;&#20110;&#24067;&#23572;&#35821;&#22659;&#12290;</div>
<div class="t-li1"><span class="t-li">2)</span> &#33509;&#27969;&#26080;&#38169;&#35823;&#19988;&#24050;&#20026; I/O &#25805;&#20316;&#23601;&#32490;&#21017;&#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#12290;&#23588;&#20854;&#26159;&#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span>fail<span class="br0">(</span><span class="br0">)</span></span></span> &#12290;</div>
<p>&#27492;&#36816;&#31639;&#31526;&#20351;&#24471;&#20197;&#27969;&#21644;&#36820;&#22238;&#21040;&#27969;&#24341;&#29992;&#30340;&#20989;&#25968;&#20026;&#24490;&#29615;&#26465;&#20214;&#21487;&#34892;&#65292;&#20135;&#29983;&#24815;&#29992;&#30340; C++ &#36755;&#20837;&#24490;&#29615;&#65292;&#20363;&#22914; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">while</span><span class="br0">(</span>stream <span class="sy1">&gt;&gt;</span> value<span class="br0">)</span> <span class="br0">{</span>...<span class="br0">}</span></span></span> &#25110; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">while</span><span class="br0">(</span>getline<span class="br0">(</span>stream, string<span class="br0">)</span><span class="br0">)</span><span class="br0">{</span>...<span class="br0">}</span></span></span> &#12290;&#36825;&#31181;&#24490;&#29615;&#20165;&#33509;&#36755;&#20837;&#25805;&#20316;&#25104;&#21151;&#25165;&#25191;&#34892;&#24490;&#29615;&#20307;&#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;&#27969;&#26080;&#38169;&#35823;&#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>
<div class="t-example">
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<pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;sstream&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> s<span class="br0">(</span><span class="st0">&quot;1 2 3 error&quot;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">int</span> n<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="sy1">&lt;&lt;</span> <span class="st0">&quot;s is &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="kw1">static_cast</span><span class="sy1">&lt;</span><span class="kw4">bool</span><span class="sy1">&gt;</span><span class="br0">(</span>s<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">while</span> <span class="br0">(</span>s <span class="sy1">&gt;&gt;</span> n<span class="br0">)</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> n <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>
<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;s is &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="kw1">static_cast</span><span class="sy1">&lt;</span><span class="kw4">bool</span><span class="sy1">&gt;</span><span class="br0">(</span>s<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></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">s is true
1
2
3
s is false</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
<p>&#19979;&#34920;&#26174;&#31034; <code>basic_ios</code> &#35775;&#38382;&#22120;&#65288; <a href="cpp-io-basic_ios-good.html"><tt>good()</tt></a>&#12289; <a href="cpp-io-basic_ios-fail.html"><tt>fail()</tt></a> &#31561;&#65289;&#23545;&#20110; <a href="cpp-io-ios_base-iostate.html"><tt>ios_base::iostate</tt></a> &#26631;&#24535;&#30340;&#25152;&#26377;&#21487;&#33021;&#32452;&#21512;&#30340;&#20540;&#65306;</p>
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<td colspan="3"><a href="cpp-io-ios_base-iostate.html"><tt>ios_base::iostate</tt></a> &#26631;&#24535;</td>
<td colspan="6"><code>basic_ios</code> &#35775;&#38382;&#22120;</td>
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<tr>
<td>eofbit</td>
<td>failbit</td>
<td>badbit</td>
<td><a href="cpp-io-basic_ios-good.html"><tt>good()</tt></a></td>
<td><a href="cpp-io-basic_ios-fail.html"><tt>fail()</tt></a></td>
<td><a href="cpp-io-basic_ios-bad.html"><tt>bad()</tt></a></td>
<td><a href="cpp-io-basic_ios-eof.html"><tt>eof()</tt></a></td>
<td><strong class="selflink"><tt>operator bool</tt></strong></td>
<td><a href="cpp-io-basic_ios-operator!.html"><tt>operator!</tt></a></td>
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<tr>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
</tr>
<tr>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
</tr>
<tr>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
</tr>
<tr>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
</tr>
<tr>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
</tr>
<tr>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
</tr>
<tr>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
</tr>
<tr>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
</tr>
</table>
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