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<title>is_virtual_base_of</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_typetraits.reference.is_virtual_base_of"></a><a class="link" href="is_virtual_base_of.html" title="is_virtual_base_of">is_virtual_base_of</a>
</h3></div></div></div>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Base</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Derived</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">is_virtual_base_of</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span>
</pre>
<p>
        <span class="bold"><strong>Inherits:</strong></span> If Base is a virtual base class
        of type Derived then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
        otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
      </p>
<p>
        Types <code class="computeroutput"><span class="identifier">Base</span></code> and <code class="computeroutput"><span class="identifier">Derived</span></code> must not be incomplete types.
      </p>
<p>
        <span class="bold"><strong>C++ Standard Reference:</strong></span> 10.
      </p>
<p>
        <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
        <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_virtual_base_of</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
        or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
      </p>
<p>
        <span class="bold"><strong>Compiler Compatibility:</strong></span> All current compilers
        are supported by this trait.
      </p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
          There are a small number of cases where it's simply not possible for this
          trait to work, and where attempting to instantiate the trait will cause
          compiler errors (see bug reports <a href="https://svn.boost.org/trac/boost/ticket/3730" target="_top">#3730</a>
          and <a href="https://svn.boost.org/trac/boost/ticket/11323" target="_top">11323</a>).
          Further more the issues may well be compiler specific. In this situation
          the user should supply a full specialization of the trait to work around
          the problem.
        </p></td></tr>
</table></div>
<p>
        <span class="bold"><strong>Examples:</strong></span>
      </p>
<div class="blockquote"><blockquote class="blockquote"><p>
          Given: <code class="computeroutput"> <span class="keyword">class</span> <span class="identifier">Base</span><span class="special">{};</span> <span class="keyword">class</span> <span class="identifier">Derived</span> <span class="special">:</span> <span class="keyword">public</span> <span class="keyword">virtual</span>
          <span class="identifier">Base</span><span class="special">{};</span></code>
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special">&lt;</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">&gt;</span></code>
          inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special">&lt;</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">&gt;::</span><span class="identifier">type</span></code> is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special">&lt;</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>true</em></span>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special">&lt;</span><span class="identifier">SomeClassType</span><span class="special">,</span>
          <span class="identifier">SomeClassType</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>true</em></span>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special">&lt;</span><span class="identifier">NotAClassType</span><span class="special">,</span>
          <span class="identifier">NotAClassType</span><span class="special">&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>false</em></span>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_virtual_base_of</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">&gt;::</span><span class="identifier">value_type</span></code>
          is the type <code class="computeroutput"><span class="keyword">bool</span></code>.
        </p></blockquote></div>
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        Distributed under the Boost Software License, Version 1.0. (See accompanying
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