<?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: Forward Iterator</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="./iterators-concepts.html" class="navigation-link">Prev</a> <a href="./bidirectional-iterator.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group">Back <a href="./bidirectional-iterator.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./iterators-concepts.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="./iterators-concepts.html" class="navigation-link">Concepts</a> / <a href="./forward-iterator.html" class="navigation-link">Forward Iterator</a></td> </tr></table><div class="header-separator"></div> <div class="section" id="forward-iterator"> <h1><a class="toc-backref" href="./iterators-concepts.html#id1450">Forward Iterator</a></h1> <div class="section" id="id384"> <h3><a class="subsection-title" href="#description" name="description">Description</a></h3> <p>A <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a> <tt class="literal"><span class="pre">i</span></tt> is a type that represents a positional reference to an element of a <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>. It allows to access the element through a dereference operation, and provides a way to obtain an iterator to the next element in a sequence.</p> <!-- A [Forward Iterator] guarantees a linear traversal over the sequence. --> </div> <div class="section" id="id385"> <h3><a class="subsection-title" href="#definitions" name="definitions">Definitions</a></h3> <ul class="simple"> <li>An iterator can be <cite>dereferenceable</cite>, meaning that <tt class="literal"><span class="pre"><a href="./deref.html" class="identifier">deref</a><i>::type</span></tt> is a well-defined expression.</li> <li>An iterator is <cite>past-the-end</cite> if it points beyond the last element of a sequence; past-the-end iterators are non-dereferenceable.</li> <li>An iterator <tt class="literal"><span class="pre">i</span></tt> is <cite>incrementable</cite> if there is a "next" iterator, that is, if <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a><i>::type</span></tt> expression is well-defined; past-the-end iterators are not incrementable.</li> <li>Two iterators into the same sequence are <cite>equivalent</cite> if they have the same type.</li> <li>An iterator <tt class="literal"><span class="pre">j</span></tt> is <cite>reachable</cite> from an iterator <tt class="literal"><span class="pre">i</span></tt> if , after recursive application of <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a></span></tt> metafunction to <tt class="literal"><span class="pre">i</span></tt> a finite number of times, <tt class="literal"><span class="pre">i</span></tt> is equivalent to <tt class="literal"><span class="pre">j</span></tt>.</li> <li>The notation [<tt class="literal"><span class="pre">i</span></tt>,<tt class="literal"><span class="pre">j</span></tt>) refers to a <cite>range</cite> of iterators beginning with <tt class="literal"><span class="pre">i</span></tt> and up to but not including <tt class="literal"><span class="pre">j</span></tt>.</li> <li>The range [<tt class="literal"><span class="pre">i</span></tt>,<tt class="literal"><span class="pre">j</span></tt>) is a <cite>valid range</cite> if <tt class="literal"><span class="pre">j</span></tt> is reachable from <tt class="literal"><span class="pre">i</span></tt>.</li> </ul> </div> <div class="section" id="id386"> <h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3> <table border="1" class="docutils table"> <colgroup> <col width="25%" /> <col width="46%" /> <col width="29%" /> </colgroup> <thead valign="bottom"> <tr><th class="head">Expression</th> <th class="head">Type</th> <th class="head">Complexity</th> </tr> </thead> <tbody valign="top"> <tr><td><tt class="literal"><span class="pre"><a href="./deref.html" class="identifier">deref</a><i>::type</span></tt></td> <td>Any type</td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a><i>::type</span></tt></td> <td><a class="reference internal" href="./forward-iterator.html">Forward Iterator</a></td> <td>Amortized constant time</td> </tr> <tr><td><tt class="literal"><span class="pre">i::category</span></tt></td> <td><a class="reference internal" href="./integral-constant.html">Integral Constant</a>, convertible to <tt class="literal"><span class="pre">forward_iterator_tag</span></tt></td> <td>Constant time</td> </tr> </tbody> </table> </div> <div class="section" id="id387"> <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3> <pre class="literal-block"> typedef <a href="./deref.html" class="identifier">deref</a><i>::type j; </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">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">i</span></tt> is dereferenceable</td> </tr> <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">j</span></tt> is identical to the type of the pointed element</td> </tr> </tbody> </table> <!-- .......................................................................... --> <pre class="literal-block"> typedef <a href="./next.html" class="identifier">next</a><i>::type j; </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">Precondition:</th><td class="field-body"><tt class="literal"><span class="pre">i</span></tt> is incrementable</td> </tr> <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">j</span></tt> is the next iterator in a sequence</td> </tr> <tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><tt class="literal"><span class="pre">j</span></tt> is dereferenceable or past-the-end</td> </tr> </tbody> </table> <!-- .......................................................................... --> <pre class="literal-block"> typedef i::category c; </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">Semantics:</th><td class="field-body"><tt class="literal"><span class="pre">c</span></tt> is identical to the iterator's category tag</td> </tr> </tbody> </table> </div> <div class="section" id="id388"> <h3><a class="subsection-title" href="#invariants" name="invariants">Invariants</a></h3> <p>For any forward iterators <tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> the following invariants always hold:</p> <ul class="simple"> <li><tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> are equivalent if and only if they are pointing to the same element.</li> <li>If <tt class="literal"><span class="pre">i</span></tt> is dereferenceable, and <tt class="literal"><span class="pre">j</span></tt> is equivalent to <tt class="literal"><span class="pre">i</span></tt>, then <tt class="literal"><span class="pre">j</span></tt> is dereferenceable as well.</li> <li>If <tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> are equivalent and dereferenceable, then <tt class="literal"><span class="pre"><a href="./deref.html" class="identifier">deref</a><i>::type</span></tt> and <tt class="literal"><span class="pre"><a href="./deref.html" class="identifier">deref</a><j>::type</span></tt> are identical.</li> <li>If <tt class="literal"><span class="pre">i</span></tt> is incrementable, and <tt class="literal"><span class="pre">j</span></tt> is equivalent to <tt class="literal"><span class="pre">i</span></tt>, then <tt class="literal"><span class="pre">j</span></tt> is incrementable as well.</li> <li>If <tt class="literal"><span class="pre">i</span></tt> and <tt class="literal"><span class="pre">j</span></tt> are equivalent and incrementable, then <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a><i>::type</span></tt> and <tt class="literal"><span class="pre"><a href="./next.html" class="identifier">next</a><j>::type</span></tt> are equivalent.</li> </ul> </div> <div class="section" id="id389"> <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="./bidirectional-iterator.html">Bidirectional Iterator</a>, <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>, <a class="reference internal" href="./deref.html">deref</a>, <a class="reference internal" href="./next.html">next</a></p> <!-- Iterators/Concepts//Bidirectional Iterator |20 --> </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="./iterators-concepts.html" class="navigation-link">Prev</a> <a href="./bidirectional-iterator.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group">Back <a href="./bidirectional-iterator.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./iterators-concepts.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. (See accompanying file 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> </html>