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<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Using function hooks</title> <link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> <link rel="up" href="../intrusive.html" title="Chapter 15. Boost.Intrusive"> <link rel="prev" href="clone_from.html" title="Cloning Boost.Intrusive containers"> <link rel="next" href="recursive.html" title="Recursive Boost.Intrusive containers"> </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="clone_from.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../intrusive.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="recursive.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="intrusive.function_hooks"></a><a class="link" href="function_hooks.html" title="Using function hooks">Using function hooks</a> </h2></div></div></div> A programmer might find that base or member hooks are not flexible enough in some situations. In some applications it would be optimal to put a hook deep inside a member of a class or just outside the class. Boost.Intrusive has an easy option to allow such cases: <code class="computeroutput"><a class="link" href="../boost/intrusive/function_hook.html" title="Struct template function_hook">function_hook</a></code>. This option is similar to <code class="computeroutput"><a class="link" href="../boost/intrusive/member_hook.html" title="Struct template member_hook">member_hook</a></code> or <code class="computeroutput"><a class="link" href="../boost/intrusive/base_hook.html" title="Struct template base_hook">base_hook</a></code>, but the programmer can specify a function object that tells the container how to obtain a hook from a value and vice versa. The programmer just needs to define the following function object: <pre class="programlisting">//This functor converts between value_type and a hook_type struct Functor { //Required types typedef /*impl-defined*/ hook_type; typedef /*impl-defined*/ hook_ptr; typedef /*impl-defined*/ const_hook_ptr; typedef /*impl-defined*/ value_type; typedef /*impl-defined*/ pointer; typedef /*impl-defined*/ const_pointer; //Required static functions static hook_ptr to_hook_ptr (value_type &value); static const_hook_ptr to_hook_ptr(const value_type &value); static pointer to_value_ptr(hook_ptr n); static const_pointer to_value_ptr(const_hook_ptr n); }; </pre> Converting from values to hooks is generally easy, since most hooks are in practice members or base classes of class data members. The inverse operation is a bit more complicated, but Boost.Intrusive offers a bit of help with the function <code class="computeroutput"><a class="link" href="../boost/intrusive/get_parent_fro_idp64070480.html" title="Function template get_parent_from_member">get_parent_from_member</a></code>, which allows easy conversions from the address of a data member to the address of the parent holding that member. Let's see a little example of <code class="computeroutput"><a class="link" href="../boost/intrusive/function_hook.html" title="Struct template function_hook">function_hook</a></code>: <pre class="programlisting">#include <boost/intrusive/list.hpp> #include <boost/intrusive/parent_from_member.hpp> using namespace boost::intrusive; struct MyClass { int dummy; //This internal type has a member hook struct InnerNode { int dummy; list_member_hook<> hook; } inner; }; //This functor converts between MyClass and InnerNode's member hook struct Functor { //Required types typedef list_member_hook<> hook_type; typedef hook_type* hook_ptr; typedef const hook_type* const_hook_ptr; typedef MyClass value_type; typedef value_type* pointer; typedef const value_type* const_pointer; //Required static functions static hook_ptr to_hook_ptr (value_type &value) { return &value.inner.hook; } static const_hook_ptr to_hook_ptr(const value_type &value) { return &value.inner.hook; } static pointer to_value_ptr(hook_ptr n) { return get_parent_from_member<MyClass> (get_parent_from_member<MyClass::InnerNode>(n, &MyClass::InnerNode::hook) ,&MyClass::inner ); } static const_pointer to_value_ptr(const_hook_ptr n) { return get_parent_from_member<MyClass> (get_parent_from_member<MyClass::InnerNode>(n, &MyClass::InnerNode::hook) ,&MyClass::inner ); } }; //Define a list that will use the hook accessed through the function object typedef list< MyClass, function_hook< Functor> > List; int main() { MyClass n; List l; //Insert the node in both lists l.insert(l.begin(), n); assert(l.size() == 1); return 0; } </pre> </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 © 2005 Olaf Krzikalla Copyright © 2006-2013 Ion Gaztanaga 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>) </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="clone_from.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../intrusive.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="recursive.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>