| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>is_base_of</title> |
| <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.74.0"> |
| <link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits"> |
| <link rel="up" href="../reference.html" title="Alphabetical Reference"> |
| <link rel="prev" href="is_array.html" title="is_array"> |
| <link rel="next" href="is_class.html" title="is_class"> |
| </head> |
| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
| <table cellpadding="2" width="100%"><tr> |
| <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> |
| <td align="center"><a href="../../../../../../index.html">Home</a></td> |
| <td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> |
| <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> |
| <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> |
| <td align="center"><a href="../../../../../../more/index.htm">More</a></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="is_array.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="is_class.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| <div class="section" lang="en"> |
| <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 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 always inherit from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>. |
| <span class="bold"><strong>This is the case even if <code class="computeroutput"><span class="identifier">X</span></code> |
| is not a class type</strong></span>. This is a change in behaviour from Boost-1.33 |
| in order to track the Technical Report on C++ Library Extensions. |
| </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> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2000, 2006 Adobe Systems Inc, David Abrahams, |
| Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, Jesse Jones, Mat |
| Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert |
| Ramey and Jeremy Siek<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>) |
| </p> |
| </div></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="is_array.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="is_class.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |
