1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Iterator Traits</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Chapter 1. Boost.Iterator"> 8<link rel="up" href="../utilities.html" title="Utilities"> 9<link rel="prev" href="concept_checking.html" title="Concept Checking"> 10<link rel="next" href="traits.html" title="Type Traits"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="concept_checking.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../utilities.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="traits.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="iterator.utilities.iterator_traits"></a><a class="link" href="iterator_traits.html" title="Iterator Traits">Iterator Traits</a> 28</h3></div></div></div> 29<p> 30 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span></code> provides access to five 31 associated types of any iterator: its <code class="computeroutput"><span class="identifier">value_type</span></code>, 32 <code class="computeroutput"><span class="identifier">reference</span></code>, <code class="computeroutput"><span class="identifier">pointer</span></code>, <code class="computeroutput"><span class="identifier">iterator_category</span></code>, 33 and <code class="computeroutput"><span class="identifier">difference_type</span></code>. Unfortunately, 34 such a "multi-valued" traits template can be difficult to use in 35 a metaprogramming context. <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">iterator</span><span class="special">/</span><span class="identifier">iterator_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 36 provides access to these types using a standard metafunctions_. 37 </p> 38<h3> 39<a name="iterator.utilities.iterator_traits.h0"></a> 40 <span class="phrase"><a name="iterator.utilities.iterator_traits.synopsis"></a></span><a class="link" href="iterator_traits.html#iterator.utilities.iterator_traits.synopsis">Synopsis</a> 41 </h3> 42<p> 43 Header <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">iterator</span><span class="special">/</span><span class="identifier">iterator_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>: 44 </p> 45<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> 46<span class="keyword">struct</span> <span class="identifier">iterator_value</span> 47<span class="special">{</span> 48 <span class="keyword">typedef</span> <span class="keyword">typename</span> 49 <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">>::</span><span class="identifier">value_type</span> 50 <span class="identifier">type</span><span class="special">;</span> 51<span class="special">};</span> 52 53<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">></span> 54<span class="keyword">struct</span> <span class="identifier">iterator_reference</span> 55<span class="special">{</span> 56 <span class="keyword">typedef</span> <span class="keyword">typename</span> 57 <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">>::</span><span class="identifier">reference</span> 58 <span class="identifier">type</span><span class="special">;</span> 59<span class="special">};</span> 60 61<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">></span> 62<span class="keyword">struct</span> <span class="identifier">iterator_pointer</span> 63<span class="special">{</span> 64 <span class="keyword">typedef</span> <span class="keyword">typename</span> 65 <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">>::</span><span class="identifier">pointer</span> 66 <span class="identifier">type</span><span class="special">;</span> 67<span class="special">};</span> 68 69<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">></span> 70<span class="keyword">struct</span> <span class="identifier">iterator_difference</span> 71<span class="special">{</span> 72 <span class="keyword">typedef</span> <span class="keyword">typename</span> 73 <span class="identifier">detail</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">>::</span><span class="identifier">difference_type</span> 74 <span class="identifier">type</span><span class="special">;</span> 75<span class="special">};</span> 76 77<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">></span> 78<span class="keyword">struct</span> <span class="identifier">iterator_category</span> 79<span class="special">{</span> 80 <span class="keyword">typedef</span> <span class="keyword">typename</span> 81 <span class="identifier">detail</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">>::</span><span class="identifier">iterator_category</span> 82 <span class="identifier">type</span><span class="special">;</span> 83<span class="special">};</span> 84</pre> 85</div> 86<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 87<td align="left"></td> 88<td align="right"><div class="copyright-footer">Copyright © 2003, 2005 David Abrahams Jeremy Siek Thomas 89 Witt<p> 90 Distributed under the Boost Software License, Version 1.0. (See accompanying 91 file LICENSE_1_0.txt or copy at <ulink url="http://www.boost.org/LICENSE_1_0.txt"> 92 http://www.boost.org/LICENSE_1_0.txt </ulink>) 93 </p> 94</div></td> 95</tr></table> 96<hr> 97<div class="spirit-nav"> 98<a accesskey="p" href="concept_checking.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../utilities.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="traits.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 99</div> 100</body> 101</html> 102
