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  26 <div class="refentry">
  27 <a name="boost.logic.tribool"></a><div class="titlepage"></div>
  28 <div class="refnamediv">
  29 <h2><span class="refentrytitle">Class tribool</span></h2>
  30 <p>boost::logic::tribool &#8212; A 3-state boolean type. </p>
  31 </div>
  32 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  33 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../tribool/reference.html#header.boost.logic.tribool_hpp" title="Header &lt;boost/logic/tribool.hpp&gt;">boost/logic/tribool.hpp</a>&gt;
  34
  35 </span>
  36 <span class="keyword">class</span> <a class="link" href="tribool.html" title="Class tribool">tribool</a> <span class="special">{</span>
  37 <span class="keyword">public</span><span class="special">:</span>
  38   <span class="keyword">enum</span> <a class="link" href="tribool/value_t.html" title="Type value_t">value_t</a><span class="special">;</span>
  39   <span class="comment">// <a class="link" href="tribool.html#boost.logic.triboolconstruct-copy-destruct">construct/copy/destruct</a></span>
  40   <a class="link" href="tribool.html#idm45206266816320-bb"><span class="identifier">tribool</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
  41   <a class="link" href="tribool.html#idm45206266758144-bb"><span class="identifier">tribool</span></a><span class="special">(</span><span class="keyword">bool</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
  42   <a class="link" href="tribool.html#idm45206266754912-bb"><span class="identifier">tribool</span></a><span class="special">(</span><span class="identifier">indeterminate_keyword_t</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span>
  43
  44   <span class="comment">// <a class="link" href="tribool.html#idm45206266820208-bb">public member functions</a></span>
  45   <span class="keyword">explicit</span> <span class="identifier">BOOST_CONSTEXPR</span> <a class="link" href="tribool.html#idm45206266819648-bb"><span class="keyword">operator</span> <span class="keyword">bool</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span>
  46
  47   <span class="comment">// public data members</span>
  48   <span class="keyword">enum</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">logic</span><span class="special">::</span><span class="identifier">tribool</span><span class="special">::</span><span class="identifier">value_t</span> <span class="identifier">value</span><span class="special">;</span>
  49 <span class="special">}</span><span class="special">;</span></pre></div>
  50 <div class="refsect1">
  51 <a name="id-1.3.24.5.2.4.4"></a><h2>Description</h2>
  52 <p>3-state boolean values are either true, false, or indeterminate. </p>
  53 <div class="refsect2">
  54 <a name="id-1.3.24.5.2.4.4.3"></a><h3>
  55 <a name="boost.logic.triboolconstruct-copy-destruct"></a><code class="computeroutput">tribool</code>
  56         public
  57        construct/copy/destruct</h3>
  58 <div class="orderedlist"><ol class="orderedlist" type="1">
  59 <li class="listitem">
  60 <pre class="literallayout"><a name="idm45206266816320-bb"></a><span class="identifier">tribool</span><span class="special">(</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></pre>
  61 <p>Construct a new 3-state boolean value with the value 'false'.</p>
  62 <p>
  63 </p>
  64 <div class="variablelist"><table border="0" class="variablelist compact">
  65 <colgroup>
  66 <col align="left" valign="top">
  67 <col>
  68 </colgroup>
  69 <tbody><tr>
  70 <td><p><span class="term">Throws:</span></p></td>
  71 <td>Will not throw.</td>
  72 </tr></tbody>
  73 </table></div>
  74 </li>
  75 <li class="listitem">
  76 <pre class="literallayout"><a name="idm45206266758144-bb"></a><span class="identifier">tribool</span><span class="special">(</span><span class="keyword">bool</span> initial_value<span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></pre>
  77 <p>Construct a new 3-state boolean value with the given boolean value, which may be <code class="computeroutput">true</code> or <code class="computeroutput">false</code>.</p>
  78 <p>
  79 </p>
  80 <div class="variablelist"><table border="0" class="variablelist compact">
  81 <colgroup>
  82 <col align="left" valign="top">
  83 <col>
  84 </colgroup>
  85 <tbody><tr>
  86 <td><p><span class="term">Throws:</span></p></td>
  87 <td>Will not throw.</td>
  88 </tr></tbody>
  89 </table></div>
  90 </li>
  91 <li class="listitem">
  92 <pre class="literallayout"><a name="idm45206266754912-bb"></a><span class="identifier">tribool</span><span class="special">(</span><span class="identifier">indeterminate_keyword_t</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></pre>
  93 <p>Construct a new 3-state boolean value with an indeterminate value.</p>
  94 <p>
  95 </p>
  96 <div class="variablelist"><table border="0" class="variablelist compact">
  97 <colgroup>
  98 <col align="left" valign="top">
  99 <col>
 100 </colgroup>
 101 <tbody><tr>
 102 <td><p><span class="term">Throws:</span></p></td>
 103 <td>Will not throw.</td>
 104 </tr></tbody>
 105 </table></div>
 106 </li>
 107 </ol></div>
 108 </div>
 109 <div class="refsect2">
 110 <a name="id-1.3.24.5.2.4.4.4"></a><h3>
 111 <a name="idm45206266820208-bb"></a><code class="computeroutput">tribool</code> public member functions</h3>
 112 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
 113 <pre class="literallayout"><span class="keyword">explicit</span> <span class="identifier">BOOST_CONSTEXPR</span> <a name="idm45206266819648-bb"></a><span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></pre>
 114 <p>Use a 3-state boolean in a boolean context. Will evaluate true in a boolean context only when the 3-state boolean is definitely true.</p>
 115 <p>
 116
 117 </p>
 118 <div class="variablelist"><table border="0" class="variablelist compact">
 119 <colgroup>
 120 <col align="left" valign="top">
 121 <col>
 122 </colgroup>
 123 <tbody>
 124 <tr>
 125 <td><p><span class="term">Returns:</span></p></td>
 126 <td><p>true if the 3-state boolean is true, false otherwise </p></td>
 127 </tr>
 128 <tr>
 129 <td><p><span class="term">Throws:</span></p></td>
 130 <td>Will not throw.</td>
 131 </tr>
 132 </tbody>
 133 </table></div>
 134 </li></ol></div>
 135 </div>
 136 </div>
 137 </div>
 138 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 139 <td align="left"></td>
 140 <td align="right"><div class="copyright-footer">Copyright &#169; 2002-2004 Douglas Gregor<p>Use, modification and distribution is subject to the Boost
 141     Software License, Version 1.0. (See accompanying file
 142     <code class="filename">LICENSE_1_0.txt</code> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</p>
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