1<?xml version="1.0" encoding="utf-8" ?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4<head> 5<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 6<meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> 7<title>The MPL Reference Manual: iterator_category</title> 8<link rel="stylesheet" href="../style.css" type="text/css" /> 9</head> 10<body class="docframe refmanual"> 11<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./deref.html" class="navigation-link">Prev</a> <a href="./algorithms.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./deref.html" class="navigation-link">Back</a> Along</span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./iterator-metafunctions.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 12<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./iterators.html" class="navigation-link">Iterators</a> / <a href="./iterator-metafunctions.html" class="navigation-link">Iterator Metafunctions</a> / <a href="./iterator-category.html" class="navigation-link">iterator_category</a></td> 13</tr></table><div class="header-separator"></div> 14<div class="section" id="iterator-category"> 15<h1><a class="toc-backref" href="./iterator-metafunctions.html#id1459">iterator_category</a></h1> 16<div class="section" id="id445"> 17<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> 18<pre class="literal-block"> 19template< 20 typename Iterator 21 > 22struct <a href="./iterator-category.html" class="identifier">iterator_category</a> 23{ 24 typedef typename Iterator::category type; 25}; 26</pre> 27</div> 28<div class="section" id="id446"> 29<h3><a class="subsection-title" href="#description" name="description">Description</a></h3> 30<p>Returns one of the following iterator category tags:</p> 31<ul class="simple"> 32<li><tt class="literal"><span class="pre">forward_iterator_tag</span></tt></li> 33<li><tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt></li> 34<li><tt class="literal"><span class="pre">random_access_iterator_tag</span></tt></li> 35</ul> 36</div> 37<div class="section" id="id447"> 38<h3><a class="subsection-title" href="#header" name="header">Header</a></h3> 39<pre class="literal-block"> 40#include <<a href="../../../../boost/mpl/iterator_category.hpp" class="header">boost/mpl/iterator_category.hpp</a>> 41#include <<a href="../../../../boost/mpl/iterator_tags.hpp" class="header">boost/mpl/iterator_tags.hpp</a>> 42</pre> 43</div> 44<div class="section" id="id448"> 45<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> 46<table border="1" class="docutils table"> 47<colgroup> 48<col width="19%" /> 49<col width="28%" /> 50<col width="53%" /> 51</colgroup> 52<thead valign="bottom"> 53<tr><th class="head">Parameter</th> 54<th class="head">Requirement</th> 55<th class="head">Description</th> 56</tr> 57</thead> 58<tbody valign="top"> 59<tr><td><tt class="literal"><span class="pre">Iterator</span></tt></td> 60<td><a class="reference internal" href="./forward-iterator.html">Forward Iterator</a></td> 61<td>The iterator to obtain a category for.</td> 62</tr> 63</tbody> 64</table> 65</div> 66<div class="section" id="id449"> 67<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> 68<p>For any <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a>s <tt class="literal"><span class="pre">iter</span></tt>:</p> 69<pre class="literal-block"> 70typedef <a href="./iterator-category.html" class="identifier">iterator_category</a><iter>::type tag; 71</pre> 72<table class="docutils field-list" frame="void" rules="none"> 73<col class="field-name" /> 74<col class="field-body" /> 75<tbody valign="top"> 76<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</p> 77</td> 78</tr> 79<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first"><tt class="literal"><span class="pre">tag</span></tt> is <tt class="literal"><span class="pre">forward_iterator_tag</span></tt> if <tt class="literal"><span class="pre">iter</span></tt> is a model of <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a>, 80<tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt> if <tt class="literal"><span class="pre">iter</span></tt> is a model of <a class="reference internal" href="./bidirectional-iterator.html">Bidirectional Iterator</a>, 81or <tt class="literal"><span class="pre">random_access_iterator_tag</span></tt> if <tt class="literal"><span class="pre">iter</span></tt> is a model of <a class="reference internal" href="./random-access-iterator.html">Random Access Iterator</a>;</p> 82</td> 83</tr> 84<tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><dl class="first last docutils"> 85<dt><tt class="literal"><span class="pre">forward_iterator_tag::value</span> <span class="pre"><</span> <span class="pre">bidirectional_iterator_tag::value</span></tt>,</dt> 86<dd><p class="first last"><tt class="literal"><span class="pre">bidirectional_iterator_tag::value</span> <span class="pre"><</span> <span class="pre">random_access_iterator_tag::value</span></tt>.</p> 87</dd> 88</dl> 89</td> 90</tr> 91</tbody> 92</table> 93</div> 94<div class="section" id="id450"> 95<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3> 96<p>Amortized constant time.</p> 97</div> 98<div class="section" id="id451"> 99<h3><a class="subsection-title" href="#example" name="example">Example</a></h3> 100<pre class="literal-block"> 101template< typename Tag, typename Iterator > 102struct algorithm_impl 103{ 104 // <em>O(n)</em> implementation 105}; 106 107template< typename Iterator > 108struct algorithm_impl<random_access_iterator_tag,Iterator> 109{ 110 // <em>O(1)</em> implementation 111}; 112 113template< typename Iterator > 114struct algorithm 115 : algorithm_impl< 116 <a href="./iterator-category.html" class="identifier">iterator_category</a><Iterator>::type 117 , Iterator 118 > 119{ 120}; 121</pre> 122</div> 123<div class="section" id="id452"> 124<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> 125<p><a class="reference internal" href="./iterators.html">Iterators</a>, <a class="reference internal" href="./begin.html">begin</a> / <a class="reference internal" href="./end.html">end</a>, <a class="reference internal" href="./advance.html">advance</a>, <a class="reference internal" href="./distance.html">distance</a>, <a class="reference internal" href="./next.html">next</a></p> 126</div> 127</div> 128 129<div class="footer-separator"></div> 130<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./deref.html" class="navigation-link">Prev</a> <a href="./algorithms.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./deref.html" class="navigation-link">Back</a> Along</span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./iterator-metafunctions.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td> 131<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> 132Distributed under the Boost Software License, Version 1.0. (See accompanying 133file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> 134</html> 135