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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"><</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">></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"><</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">></span></code> |
| or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</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">></span></code> |
| </p> |
| <p> |
| <span class="bold"><strong>Compiler Compatibility:</strong></span> this trait also |
| requires a working <a class="link" href="is_base_of.html" title="is_base_of">is_base_of</a> |
| 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 report <a href="https://svn.boost.org/trac/boost/ticket/3730" target="_top">#3730</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"><</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">></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"><</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">>::</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"><</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Derived</span><span class="special">>::</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"><</span><span class="identifier">SomeClassType</span><span class="special">,</span> |
| <span class="identifier">SomeClassType</span><span class="special">>::</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"><</span><span class="identifier">NotAClassType</span><span class="special">,</span> |
| <span class="identifier">NotAClassType</span><span class="special">>::</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"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">U</span><span class="special">>::</span><span class="identifier">value_type</span></code> |
| is the type <code class="computeroutput"><span class="keyword">bool</span></code>. |
| </p></blockquote></div> |
| </div> |
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| Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven |
| Watanabe<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
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