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>Move iterators</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="../move.html" title="Chapter 25. Boost.Move"> 10<link rel="prev" href="move_return.html" title="Implicit Move when returning a local object"> 11<link rel="next" href="move_inserters.html" title="Move inserters"> 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="move_return.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../move.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="move_inserters.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="move.move_iterator"></a><a class="link" href="move_iterator.html" title="Move iterators">Move iterators</a> 29</h2></div></div></div> 30<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">></span> 31<span class="keyword">class</span> <span class="identifier">move_iterator</span><span class="special">;</span> 32 33<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">It</span><span class="special">></span> 34<span class="identifier">move_iterator</span><span class="special"><</span><span class="identifier">It</span><span class="special">></span> <span class="identifier">make_move_iterator</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">It</span> <span class="special">&</span><span class="identifier">it</span><span class="special">);</span> 35</pre> 36<p> 37 <code class="computeroutput"><a class="link" href="../boost/move_iterator.html" title="Class template move_iterator">move_iterator</a></code> is an iterator 38 adaptor with the same behavior as the underlying iterator except that its dereference 39 operator implicitly converts the value returned by the underlying iterator's 40 dereference operator to a rvalue reference: <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">underlying_iterator</span><span class="special">)</span></code> 41 It is a read-once iterator, but can have up to random access traversal characteristics. 42 </p> 43<p> 44 <code class="computeroutput"><span class="identifier">move_iterator</span></code> is very useful 45 because some generic algorithms and container insertion functions can be called 46 with move iterators to replace copying with moving. For example: 47 </p> 48<p> 49</p> 50<pre class="programlisting"><span class="comment">//header file "movable.hpp"</span> 51<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">move</span><span class="special">/</span><span class="identifier">core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 52<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">move</span><span class="special">/</span><span class="identifier">traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 53 54<span class="comment">//A movable class</span> 55<span class="keyword">class</span> <span class="identifier">movable</span> 56<span class="special">{</span> 57 <span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">movable</span><span class="special">)</span> 58 <span class="keyword">int</span> <span class="identifier">value_</span><span class="special">;</span> 59 60 <span class="keyword">public</span><span class="special">:</span> 61 <span class="identifier">movable</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">value_</span><span class="special">(</span><span class="number">1</span><span class="special">){}</span> 62 63 <span class="comment">//Move constructor and assignment</span> 64 <span class="identifier">movable</span><span class="special">(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">movable</span><span class="special">)</span> <span class="identifier">m</span><span class="special">)</span> 65 <span class="special">{</span> <span class="identifier">value_</span> <span class="special">=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">value_</span><span class="special">;</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">value_</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="special">}</span> 66 67 <span class="identifier">movable</span> <span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">movable</span><span class="special">)</span> <span class="identifier">m</span><span class="special">)</span> 68 <span class="special">{</span> <span class="identifier">value_</span> <span class="special">=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">value_</span><span class="special">;</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">value_</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span> <span class="special">}</span> 69 70 <span class="keyword">bool</span> <span class="identifier">moved</span><span class="special">()</span> <span class="keyword">const</span> <span class="comment">//Observer</span> 71 <span class="special">{</span> <span class="keyword">return</span> <span class="special">!</span><span class="identifier">value_</span><span class="special">;</span> <span class="special">}</span> 72 73 <span class="keyword">int</span> <span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span> <span class="comment">//Observer</span> 74 <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">value_</span><span class="special">;</span> <span class="special">}</span> 75<span class="special">};</span> 76 77<span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> 78 79<span class="keyword">template</span><span class="special"><></span> 80<span class="keyword">struct</span> <span class="identifier">has_nothrow_move</span><span class="special"><</span><span class="identifier">movable</span><span class="special">></span> 81<span class="special">{</span> 82 <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">value</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span> 83<span class="special">};</span> 84 85<span class="special">}</span> <span class="comment">//namespace boost{</span> 86</pre> 87<p> 88 </p> 89<p> 90 <code class="computeroutput"><span class="identifier">movable</span></code> objects can be moved 91 from one container to another using move iterators and insertion and assignment 92 operations.w 93 </p> 94<p> 95</p> 96<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 97<span class="preprocessor">#include</span> <span class="string">"movable.hpp"</span> 98<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span> 99 100<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 101<span class="special">{</span> 102 <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">container</span><span class="special">;</span> 103 104 <span class="comment">//Create a vector with 10 default constructed objects</span> 105 <span class="identifier">vector</span><span class="special"><</span><span class="identifier">movable</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="number">10</span><span class="special">);</span> 106 <span class="identifier">assert</span><span class="special">(!</span><span class="identifier">v</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">moved</span><span class="special">());</span> 107 108 <span class="comment">//Move construct all elements in v into v2</span> 109 <span class="identifier">vector</span><span class="special"><</span><span class="identifier">movable</span><span class="special">></span> <span class="identifier">v2</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_move_iterator</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">begin</span><span class="special">())</span> 110 <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_move_iterator</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">end</span><span class="special">()));</span> 111 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">moved</span><span class="special">());</span> 112 <span class="identifier">assert</span><span class="special">(!</span><span class="identifier">v2</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">moved</span><span class="special">());</span> 113 114 <span class="comment">//Now move assign all elements from in v2 back into v</span> 115 <span class="identifier">v</span><span class="special">.</span><span class="identifier">assign</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_move_iterator</span><span class="special">(</span><span class="identifier">v2</span><span class="special">.</span><span class="identifier">begin</span><span class="special">())</span> 116 <span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_move_iterator</span><span class="special">(</span><span class="identifier">v2</span><span class="special">.</span><span class="identifier">end</span><span class="special">()));</span> 117 <span class="identifier">assert</span><span class="special">(</span><span class="identifier">v2</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">moved</span><span class="special">());</span> 118 <span class="identifier">assert</span><span class="special">(!</span><span class="identifier">v</span><span class="special">[</span><span class="number">0</span><span class="special">].</span><span class="identifier">moved</span><span class="special">());</span> 119 120 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 121<span class="special">}</span> 122</pre> 123<p> 124 </p> 125</div> 126<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 127<td align="left"></td> 128<td align="right"><div class="copyright-footer">Copyright © 2008-2014 Ion Gaztanaga<p> 129 Distributed under the Boost Software License, Version 1.0. (See accompanying 130 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>) 131 </p> 132</div></td> 133</tr></table> 134<hr> 135<div class="spirit-nav"> 136<a accesskey="p" href="move_return.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../move.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="move_inserters.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 137</div> 138</body> 139</html> 140
