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>Cloning Boost.Intrusive containers</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="erasing_and_disposing.html" title="Erasing and disposing values from Boost.Intrusive containers"> 11<link rel="next" href="function_hooks.html" title="Using function hooks"> 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="erasing_and_disposing.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="function_hooks.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.clone_from"></a><a class="link" href="clone_from.html" title="Cloning Boost.Intrusive containers">Cloning Boost.Intrusive containers</a> 29</h2></div></div></div> 30<p> 31 As previously mentioned, <span class="bold"><strong>Boost.Intrusive</strong></span> containers 32 are <span class="bold"><strong>non-copyable and non-assignable</strong></span>, because 33 intrusive containers don't allocate memory at all. To implement a copy-constructor 34 or assignment operator, the user must clone one by one all the elements of 35 the container and insert them in another intrusive container. However, cloning 36 by hand is usually more inefficient than a member cloning function and a specialized 37 cloning function can offer more guarantees than the manual cloning (better 38 exception safety guarantees, for example). 39 </p> 40<p> 41 To ease the implementation of copy constructors and assignment operators of 42 classes containing <span class="bold"><strong>Boost.Intrusive</strong></span> containers, 43 all <span class="bold"><strong>Boost.Intrusive</strong></span> containers offer a special 44 cloning function called <code class="computeroutput"><span class="identifier">clone_from</span></code>. 45 </p> 46<p> 47 Apart from the container to be cloned, <code class="computeroutput"><span class="identifier">clone_from</span></code> 48 takes two function objects as arguments. For example, consider the <code class="computeroutput"><span class="identifier">clone_from</span></code> member function of <code class="computeroutput"><a class="link" href="../boost/intrusive/list.html" title="Class template list">list</a></code>: 49 </p> 50<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Cloner</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Disposer</span><span class="special">></span> 51<span class="keyword">void</span> <span class="identifier">clone_from</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">list</span> <span class="special">&</span><span class="identifier">src</span><span class="special">,</span> <span class="identifier">Cloner</span> <span class="identifier">cloner</span><span class="special">,</span> <span class="identifier">Disposer</span> <span class="identifier">disposer</span><span class="special">);</span> 52</pre> 53<p> 54 This function will make <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> 55 a clone of <code class="computeroutput"><span class="identifier">src</span></code>. Let's explain 56 the arguments: 57 </p> 58<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 59<li class="listitem"> 60 The first parameter is the list to be cloned. 61 </li> 62<li class="listitem"> 63 The second parameter is a function object that will clone <code class="computeroutput"><span class="identifier">value_type</span></code> objects and return a pointer 64 to the clone. It must implement the following function: <code class="computeroutput"><span class="identifier">pointer</span> 65 <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">value_type</span> 66 <span class="special">&)</span></code>. 67 </li> 68<li class="listitem"> 69 The second parameter is a function object that will dispose <code class="computeroutput"><span class="identifier">value_type</span></code> objects. It's used first to 70 empty the container before cloning and to dispose the elements if an exception 71 is thrown. 72 </li> 73</ul></div> 74<p> 75 The cloning function works as follows: 76 </p> 77<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 78<li class="listitem"> 79 First it clears and disposes all the elements from *this using the disposer 80 function object. 81 </li> 82<li class="listitem"> 83 After that it starts cloning all the elements of the source container using 84 the cloner function object. 85 </li> 86<li class="listitem"> 87 If any operation in the cloning function (for example, the cloner function 88 object) throws, all the constructed elements are disposed using the disposer 89 function object. 90 </li> 91</ul></div> 92<p> 93 Here is an example of <code class="computeroutput"><span class="identifier">clone_from</span></code>: 94 </p> 95<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> 96<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 97<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span> 98 99<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> 100 101<span class="comment">//A class that can be inserted in an intrusive list</span> 102<span class="keyword">class</span> <span class="identifier">my_class</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">list_base_hook</span><span class="special"><></span> 103<span class="special">{</span> 104 <span class="keyword">public</span><span class="special">:</span> 105 <span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span><span class="keyword">const</span> <span class="identifier">my_class</span> <span class="special">&</span><span class="identifier">a</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">my_class</span> <span class="special">&</span><span class="identifier">b</span><span class="special">)</span> 106 <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">int_</span> <span class="special">==</span> <span class="identifier">b</span><span class="special">.</span><span class="identifier">int_</span><span class="special">;</span> <span class="special">}</span> 107 108 <span class="keyword">int</span> <span class="identifier">int_</span><span class="special">;</span> 109 110 <span class="comment">//...</span> 111<span class="special">};</span> 112 113<span class="comment">//Definition of the intrusive list</span> 114<span class="keyword">typedef</span> <span class="identifier">list</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">></span> <span class="identifier">my_class_list</span><span class="special">;</span> 115 116<span class="comment">//Cloner object function</span> 117<span class="keyword">struct</span> <span class="identifier">new_cloner</span> 118<span class="special">{</span> 119 <span class="identifier">my_class</span> <span class="special">*</span><span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">my_class</span> <span class="special">&</span><span class="identifier">clone_this</span><span class="special">)</span> 120 <span class="special">{</span> <span class="keyword">return</span> <span class="keyword">new</span> <span class="identifier">my_class</span><span class="special">(</span><span class="identifier">clone_this</span><span class="special">);</span> <span class="special">}</span> 121<span class="special">};</span> 122 123<span class="comment">//The disposer object function</span> 124<span class="keyword">struct</span> <span class="identifier">delete_disposer</span> 125<span class="special">{</span> 126 <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">my_class</span> <span class="special">*</span><span class="identifier">delete_this</span><span class="special">)</span> 127 <span class="special">{</span> <span class="keyword">delete</span> <span class="identifier">delete_this</span><span class="special">;</span> <span class="special">}</span> 128<span class="special">};</span> 129 130<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 131<span class="special">{</span> 132 <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">MaxElem</span> <span class="special">=</span> <span class="number">100</span><span class="special">;</span> 133 <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">my_class</span><span class="special">></span> <span class="identifier">nodes</span><span class="special">(</span><span class="identifier">MaxElem</span><span class="special">);</span> 134 135 <span class="comment">//Fill all the nodes and insert them in the list</span> 136 <span class="identifier">my_class_list</span> <span class="identifier">list</span><span class="special">;</span> 137 138 <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="identifier">MaxElem</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">nodes</span><span class="special">[</span><span class="identifier">i</span><span class="special">].</span><span class="identifier">int_</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> 139 140 <span class="identifier">list</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> <span class="identifier">nodes</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">nodes</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span> 141 142 <span class="comment">//Now clone "list" using "new" and "delete" object functions</span> 143 <span class="identifier">my_class_list</span> <span class="identifier">cloned_list</span><span class="special">;</span> 144 <span class="identifier">cloned_list</span><span class="special">.</span><span class="identifier">clone_from</span><span class="special">(</span><span class="identifier">list</span><span class="special">,</span> <span class="identifier">new_cloner</span><span class="special">(),</span> <span class="identifier">delete_disposer</span><span class="special">());</span> 145 146 <span class="comment">//Test that both are equal</span> 147 <span class="keyword">if</span><span class="special">(</span><span class="identifier">cloned_list</span> <span class="special">!=</span> <span class="identifier">list</span><span class="special">)</span> 148 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Both lists are different"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 149 <span class="keyword">else</span> 150 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Both lists are equal"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 151 152 <span class="comment">//Don't forget to free the memory from the second list</span> 153 <span class="identifier">cloned_list</span><span class="special">.</span><span class="identifier">clear_and_dispose</span><span class="special">(</span><span class="identifier">delete_disposer</span><span class="special">());</span> 154 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 155<span class="special">}</span> 156</pre> 157</div> 158<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 159<td align="left"></td> 160<td align="right"><div class="copyright-footer">Copyright © 2005 Olaf Krzikalla<br>Copyright © 2006-2015 Ion Gaztanaga<p> 161 Distributed under the Boost Software License, Version 1.0. (See accompanying 162 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>) 163 </p> 164</div></td> 165</tr></table> 166<hr> 167<div class="spirit-nav"> 168<a accesskey="p" href="erasing_and_disposing.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="function_hooks.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 169</div> 170</body> 171</html> 172
