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<div class="section boost_typetraits_reference_is_base_of">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_typetraits.reference.is_base_of"></a><a class="link" href="is_base_of.html" title="is_base_of">is_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_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 base class of type
Derived or if both types are the same class type 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>
This template will detect non-public base classes, and ambiguous base classes.
</p>
<p>
Note that <code class="computeroutput"><span class="identifier">is_base_of</span><span class="special"><</span><span class="identifier">X</span><span class="special">,</span><span class="identifier">X</span><span class="special">></span></code> will inherit from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>
if X is a class type. This is a change in behaviour from Boost-1.39.0 in
order to track the emerging C++0x standard.
</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_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> If the compiler
does not support partial-specialization of class templates, then this template
can not be used with function types. There are some older compilers which
will produce compiler errors if <code class="computeroutput"><span class="identifier">Base</span></code>
is a private base class of <code class="computeroutput"><span class="identifier">Derived</span></code>,
or if <code class="computeroutput"><span class="identifier">Base</span></code> is an ambiguous
base of <code class="computeroutput"><span class="identifier">Derived</span></code>. These compilers
include Borland C++, older versions of Sun Forte C++, Digital Mars C++, and
older versions of EDG based compilers.
</p>
<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="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_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_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_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_base_of</span><span class="special"><</span><span class="identifier">Base</span><span class="special">,</span> <span class="identifier">Base</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>: a class is regarded as it's
own base.
</p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
<code class="computeroutput"><span class="identifier">is_base_of</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">T</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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<td align="right"><div class="copyright-footer">Copyright © 2000, 2011 Adobe Systems Inc, David Abrahams,
Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant,
Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten
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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