<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> <title>The MPL Reference Manual: iterator_category</title> <link rel="stylesheet" href="../style.css" type="text/css" /> </head> <body class="docframe refmanual"> <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> <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> </tr></table><div class="header-separator"></div> <div class="section" id="iterator-category"> <h1><a class="toc-backref" href="./iterator-metafunctions.html#id1459">iterator_category</a></h1> <div class="section" id="id445"> <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3> <pre class="literal-block"> template< typename Iterator > struct <a href="./iterator-category.html" class="identifier">iterator_category</a> { typedef typename Iterator::category type; }; </pre> </div> <div class="section" id="id446"> <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> <p>Returns one of the following iterator category tags:</p> <ul class="simple"> <li><tt class="literal"><span class="pre">forward_iterator_tag</span></tt></li> <li><tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt></li> <li><tt class="literal"><span class="pre">random_access_iterator_tag</span></tt></li> </ul> </div> <div class="section" id="id447"> <h3><a class="subsection-title" href="#header" name="header">Header</a></h3> <pre class="literal-block"> #include <<a href="../../../../boost/mpl/iterator_category.hpp" class="header">boost/mpl/iterator_category.hpp</a>> #include <<a href="../../../../boost/mpl/iterator_tags.hpp" class="header">boost/mpl/iterator_tags.hpp</a>> </pre> </div> <div class="section" id="id448"> <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3> <table border="1" class="docutils table"> <colgroup> <col width="19%" /> <col width="28%" /> <col width="53%" /> </colgroup> <thead valign="bottom"> <tr><th class="head">Parameter</th> <th class="head">Requirement</th> <th class="head">Description</th> </tr> </thead> <tbody valign="top"> <tr><td><tt class="literal"><span class="pre">Iterator</span></tt></td> <td><a class="reference internal" href="./forward-iterator.html">Forward Iterator</a></td> <td>The iterator to obtain a category for.</td> </tr> </tbody> </table> </div> <div class="section" id="id449"> <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> <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> <pre class="literal-block"> typedef <a href="./iterator-category.html" class="identifier">iterator_category</a><iter>::type tag; </pre> <table class="docutils field-list" frame="void" rules="none"> <col class="field-name" /> <col class="field-body" /> <tbody valign="top"> <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> </td> </tr> <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>, <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>, or <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> </td> </tr> <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><dl class="first last docutils"> <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> <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> </dd> </dl> </td> </tr> </tbody> </table> </div> <div class="section" id="id450"> <h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3> <p>Amortized constant time.</p> </div> <div class="section" id="id451"> <h3><a class="subsection-title" href="#example" name="example">Example</a></h3> <pre class="literal-block"> template< typename Tag, typename Iterator > struct algorithm_impl { // <em>O(n)</em> implementation }; template< typename Iterator > struct algorithm_impl<random_access_iterator_tag,Iterator> { // <em>O(1)</em> implementation }; template< typename Iterator > struct algorithm : algorithm_impl< <a href="./iterator-category.html" class="identifier">iterator_category</a><Iterator>::type , Iterator > { }; </pre> </div> <div class="section" id="id452"> <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3> <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> </div> </div> <div class="footer-separator"></div> <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> <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> Distributed under the Boost Software License, Version 1.0. 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