185 lines
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185 lines
16 KiB
HTML
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<title>std::basic_ios<CharT,Traits>::bad</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_ios_bad 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_ios<CharT,Traits>::</span>bad</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_ios.html">basic ios</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> bad<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<p>若关联的流上已出现不可恢复的错误则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。尤其是若 <span class="t-c"><span class="mw-geshi cpp source-cpp">rdstate<span class="br0">(</span><span class="br0">)</span></span></span> 中设置了 <a href="cpp-io-ios_base-iostate.html"><tt>badbit</tt></a> 则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 。</p>
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<p>设置 <code>badbit</code> 的条件列表见 <a href="cpp-io-ios_base-iostate.html"><tt>ios_base::iostate</tt></a> 。</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>若出现不可恢复的错误则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ,否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</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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<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="co2">#include <cstdlib></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_ifstream.html"><span class="kw1732">std::<span class="me2">ifstream</span></span></a> file<span class="br0">(</span><span class="st0">"test.txt"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span><span class="sy3">!</span>file<span class="br0">)</span> <span class="co1">// operator! 用于此</span>
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<span class="br0">{</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">"File opening failed<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">return</span> <a href="cpp-utility-program-EXIT_status.html"><span class="kw973">EXIT_FAILURE</span></a><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="co1">// 典型的 C++ I/O 循环以 I/O 函数的返回值为循环控制条件,</span>
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<span class="co1">// operator bool() 用于此</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> n<span class="sy4">;</span> file <span class="sy1">>></span> n<span class="sy4">;</span> <span class="br0">)</span> <span class="br0">{</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> n <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<span class="br0">}</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">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>file.<span class="me1">bad</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</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">"I/O error while reading<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">else</span> <span class="kw1">if</span> <span class="br0">(</span>file.<span class="me1">eof</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</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">"End of file reached successfully<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">else</span> <span class="kw1">if</span> <span class="br0">(</span>file.<span class="me1">fail</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</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">"Non-integer data encountered<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span></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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<p>下表显示 <code>basic_ios</code> 访问器( <a href="cpp-io-basic_ios-good.html"><tt>good()</tt></a>、 <a href="cpp-io-basic_ios-fail.html"><tt>fail()</tt></a> 等)对于 <a href="cpp-io-ios_base-iostate.html"><tt>ios_base::iostate</tt></a> 标志的所有可能组合的值:</p>
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<table class="wikitable" style="font-size:85%; text-align:center;">
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<tr>
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<td colspan="3"><a href="cpp-io-ios_base-iostate.html"><tt>ios_base::iostate</tt></a> 标志</td>
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<td colspan="6"><code>basic_ios</code> 访问器</td>
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<tr>
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<td>eofbit</td>
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<td>failbit</td>
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<td>badbit</td>
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<td><a href="cpp-io-basic_ios-good.html"><tt>good()</tt></a></td>
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<td><a href="cpp-io-basic_ios-fail.html"><tt>fail()</tt></a></td>
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<td><strong class="selflink"><tt>bad()</tt></strong></td>
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<td><a href="cpp-io-basic_ios-eof.html"><tt>eof()</tt></a></td>
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<td><a href="cpp-io-basic_ios-operator_bool.html"><tt>operator bool</tt></a></td>
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<td><a href="cpp-io-basic_ios-operator!.html"><tt>operator!</tt></a></td>
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</tr>
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<tr>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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</tr>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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</tr>
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<tr>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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</tr>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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</tr>
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<tr>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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</tr>
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<tr>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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</tr>
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<tr>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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</tr>
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<tr>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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<td style="background:#ff9090; color:black; vertical-align: middle; text-align: center;" class="table-no">false</td>
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<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">true</td>
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