1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Using function hooks</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../intrusive.html" title="Chapter 19. Boost.Intrusive"> 10<link rel="prev" href="clone_from.html" title="Cloning Boost.Intrusive containers"> 11<link rel="next" href="recursive.html" title="Recursive Boost.Intrusive containers"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<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> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="intrusive.function_hooks"></a><a class="link" href="function_hooks.html" title="Using function hooks">Using function hooks</a> 29</h2></div></div></div> 30<p> 31 A programmer might find that base or member hooks are not flexible enough in 32 some situations. In some applications it would be optimal to put a hook deep 33 inside a member of a class or just outside the class. <span class="bold"><strong>Boost.Intrusive</strong></span> 34 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>. 35 </p> 36<p> 37 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> 38 or <code class="computeroutput"><a class="link" href="../boost/intrusive/base_hook.html" title="Struct template base_hook">base_hook</a></code>, but 39 the programmer can specify a function object that tells the container how to 40 obtain a hook from a value and vice versa. The programmer just needs to define 41 the following function object: 42 </p> 43<pre class="programlisting"><span class="comment">//This functor converts between value_type and a hook_type</span> 44<span class="keyword">struct</span> <span class="identifier">Functor</span> 45<span class="special">{</span> 46 <span class="comment">//Required types</span> 47 <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">hook_type</span><span class="special">;</span> 48 <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">hook_ptr</span><span class="special">;</span> 49 <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">const_hook_ptr</span><span class="special">;</span> 50 <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">value_type</span><span class="special">;</span> 51 <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">pointer</span><span class="special">;</span> 52 <span class="keyword">typedef</span> <span class="comment">/*impl-defined*/</span> <span class="identifier">const_pointer</span><span class="special">;</span> 53 <span class="comment">//Required static functions</span> 54 <span class="keyword">static</span> <span class="identifier">hook_ptr</span> <span class="identifier">to_hook_ptr</span> <span class="special">(</span><span class="identifier">value_type</span> <span class="special">&</span><span class="identifier">value</span><span class="special">);</span> 55 <span class="keyword">static</span> <span class="identifier">const_hook_ptr</span> <span class="identifier">to_hook_ptr</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&</span><span class="identifier">value</span><span class="special">);</span> 56 <span class="keyword">static</span> <span class="identifier">pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">hook_ptr</span> <span class="identifier">n</span><span class="special">);</span> 57 <span class="keyword">static</span> <span class="identifier">const_pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">const_hook_ptr</span> <span class="identifier">n</span><span class="special">);</span> 58<span class="special">};</span> 59</pre> 60<p> 61 Converting from values to hooks is generally easy, since most hooks are in 62 practice members or base classes of class data members. The inverse operation 63 is a bit more complicated, but <span class="bold"><strong>Boost.Intrusive</strong></span> 64 offers a bit of help with the function <code class="computeroutput"><a class="link" href="../boost/intrusive/get_pare_idm45020921461200.html" title="Function template get_parent_from_member">get_parent_from_member</a></code>, 65 which allows easy conversions from the address of a data member to the address 66 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>: 67 </p> 68<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 69<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">intrusive</span><span class="special">/</span><span class="identifier">parent_from_member</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 70 71<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">intrusive</span><span class="special">;</span> 72 73<span class="keyword">struct</span> <span class="identifier">MyClass</span> 74<span class="special">{</span> 75 <span class="keyword">int</span> <span class="identifier">dummy</span><span class="special">;</span> 76 <span class="comment">//This internal type has a member hook</span> 77 <span class="keyword">struct</span> <span class="identifier">InnerNode</span> 78 <span class="special">{</span> 79 <span class="keyword">int</span> <span class="identifier">dummy</span><span class="special">;</span> 80 <span class="identifier">list_member_hook</span><span class="special"><></span> <span class="identifier">hook</span><span class="special">;</span> 81 <span class="special">}</span> <span class="identifier">inner</span><span class="special">;</span> 82<span class="special">};</span> 83 84<span class="comment">//This functor converts between MyClass and InnerNode's member hook</span> 85<span class="keyword">struct</span> <span class="identifier">Functor</span> 86<span class="special">{</span> 87 <span class="comment">//Required types</span> 88 <span class="keyword">typedef</span> <span class="identifier">list_member_hook</span><span class="special"><></span> <span class="identifier">hook_type</span><span class="special">;</span> 89 <span class="keyword">typedef</span> <span class="identifier">hook_type</span><span class="special">*</span> <span class="identifier">hook_ptr</span><span class="special">;</span> 90 <span class="keyword">typedef</span> <span class="keyword">const</span> <span class="identifier">hook_type</span><span class="special">*</span> <span class="identifier">const_hook_ptr</span><span class="special">;</span> 91 <span class="keyword">typedef</span> <span class="identifier">MyClass</span> <span class="identifier">value_type</span><span class="special">;</span> 92 <span class="keyword">typedef</span> <span class="identifier">value_type</span><span class="special">*</span> <span class="identifier">pointer</span><span class="special">;</span> 93 <span class="keyword">typedef</span> <span class="keyword">const</span> <span class="identifier">value_type</span><span class="special">*</span> <span class="identifier">const_pointer</span><span class="special">;</span> 94 95 <span class="comment">//Required static functions</span> 96 <span class="keyword">static</span> <span class="identifier">hook_ptr</span> <span class="identifier">to_hook_ptr</span> <span class="special">(</span><span class="identifier">value_type</span> <span class="special">&</span><span class="identifier">value</span><span class="special">)</span> 97 <span class="special">{</span> <span class="keyword">return</span> <span class="special">&</span><span class="identifier">value</span><span class="special">.</span><span class="identifier">inner</span><span class="special">.</span><span class="identifier">hook</span><span class="special">;</span> <span class="special">}</span> 98 <span class="keyword">static</span> <span class="identifier">const_hook_ptr</span> <span class="identifier">to_hook_ptr</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&</span><span class="identifier">value</span><span class="special">)</span> 99 <span class="special">{</span> <span class="keyword">return</span> <span class="special">&</span><span class="identifier">value</span><span class="special">.</span><span class="identifier">inner</span><span class="special">.</span><span class="identifier">hook</span><span class="special">;</span> <span class="special">}</span> 100 <span class="keyword">static</span> <span class="identifier">pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">hook_ptr</span> <span class="identifier">n</span><span class="special">)</span> 101 <span class="special">{</span> 102 <span class="keyword">return</span> <span class="identifier">get_parent_from_member</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> 103 <span class="special">(</span><span class="identifier">get_parent_from_member</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">>(</span><span class="identifier">n</span><span class="special">,</span> <span class="special">&</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">::</span><span class="identifier">hook</span><span class="special">)</span> 104 <span class="special">,&</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">inner</span> 105 <span class="special">);</span> 106 <span class="special">}</span> 107 <span class="keyword">static</span> <span class="identifier">const_pointer</span> <span class="identifier">to_value_ptr</span><span class="special">(</span><span class="identifier">const_hook_ptr</span> <span class="identifier">n</span><span class="special">)</span> 108 <span class="special">{</span> 109 <span class="keyword">return</span> <span class="identifier">get_parent_from_member</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> 110 <span class="special">(</span><span class="identifier">get_parent_from_member</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">>(</span><span class="identifier">n</span><span class="special">,</span> <span class="special">&</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">InnerNode</span><span class="special">::</span><span class="identifier">hook</span><span class="special">)</span> 111 <span class="special">,&</span><span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">inner</span> 112 <span class="special">);</span> 113 <span class="special">}</span> 114<span class="special">};</span> 115 116<span class="comment">//Define a list that will use the hook accessed through the function object</span> 117<span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span> <span class="identifier">MyClass</span><span class="special">,</span> <span class="identifier">function_hook</span><span class="special"><</span> <span class="identifier">Functor</span><span class="special">></span> <span class="special">></span> <span class="identifier">List</span><span class="special">;</span> 118 119<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 120<span class="special">{</span> 121 <span class="identifier">MyClass</span> <span class="identifier">n</span><span class="special">;</span> 122 <span class="identifier">List</span> <span class="identifier">l</span><span class="special">;</span> 123 <span class="comment">//Insert the node in both lists</span> 124 <span class="identifier">l</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">n</span><span class="special">);</span> 125 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> 126 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 127<span class="special">}</span> 128</pre> 129</div> 130<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 131<td align="left"></td> 132<td align="right"><div class="copyright-footer">Copyright © 2005 Olaf Krzikalla<br>Copyright © 2006-2015 Ion Gaztanaga<p> 133 Distributed under the Boost Software License, Version 1.0. (See accompanying 134 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>) 135 </p> 136</div></td> 137</tr></table> 138<hr> 139<div class="spirit-nav"> 140<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> 141</div> 142</body> 143</html> 144
