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>Concept ForwardIterator</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="concept_check.html#concepts.reference" title="Concept reference"> 10<link rel="prev" href="OutputIterator.html" title="Concept OutputIterator"> 11<link rel="next" href="BidirectionalIterator.html" title="Concept BidirectionalIterator"> 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="OutputIterator.html"><img src="../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="concept_check.html#concepts.reference"><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="BidirectionalIterator.html"><img src="../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="refentry"> 27<a name="ForwardIterator"></a><div class="titlepage"></div> 28<div class="refnamediv"> 29<h2><span class="refentrytitle">Concept ForwardIterator</span></h2> 30<p>ForwardIterator</p> 31</div> 32<div class="refsect1"> 33<a name="id-1.3.49.3.7.3"></a><h2>Description</h2> 34<p>A forward iterator is an iterator that can read through a sequence of 35 values. It is multi-pass (old values of the iterator can be 36 re-used), and can be either mutable (data pointed to by it can be 37 changed) or not mutable.</p> 38<p>An iterator represents a position in a sequence. Therefore, the 39 iterator can point into the sequence (returning a value when dereferenced 40 and being incrementable), or be off-the-end (and not dereferenceable or 41 incrementable).</p> 42</div> 43<div class="refsect1"> 44<a name="id-1.3.49.3.7.4"></a><h2>Refinement of</h2> 45<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 46<li class="listitem"><p><a class="link" href="InputIterator.html" title="Concept InputIterator">InputIterator</a></p></li> 47<li class="listitem"><p><a class="link" href="OutputIterator.html" title="Concept OutputIterator">OutputIterator</a></p></li> 48</ul></div> 49</div> 50<div class="refsect1"> 51<a name="id-1.3.49.3.7.5"></a><h2>Associated types</h2> 52<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 53<li class="listitem"> 54<p><span class="bold"><strong>value_type</strong></span></p> 55<pre class="literallayout">std::iterator_traits<Iter>::value_type</pre> 56<p>The value type of the iterator</p> 57</li> 58<li class="listitem"> 59<p><span class="bold"><strong>category</strong></span></p> 60<pre class="literallayout">std::iterator_traits<Iter>::iterator_category</pre> 61<p>The category of the iterator</p> 62</li> 63</ul></div> 64</div> 65<div class="refsect1"> 66<a name="id-1.3.49.3.7.6"></a><h2>Notation</h2> 67<div class="variablelist"><dl class="variablelist"> 68<dt><span class="term">Iter</span></dt> 69<dd>A type playing the role of iterator-type in the <a class="link" href="ForwardIterator.html" title="Concept ForwardIterator">ForwardIterator</a> concept.</dd> 70<dt> 71<span class="term"><code class="varname">i</code>, </span><span class="term"><code class="varname">j</code></span> 72</dt> 73<dd>Objects of type Iter</dd> 74<dt><span class="term"><code class="varname">x</code></span></dt> 75<dd>Object of type value_type</dd> 76</dl></div> 77</div> 78<div class="refsect1"> 79<a name="id-1.3.49.3.7.7"></a><h2>Type expressions</h2> 80<div class="variablelist"><dl class="variablelist"> 81<dt><span class="term">Category tag</span></dt> 82<dd><p><span class="type">category</span> must be 83 derived from <span class="type">std::forward_iterator_tag</span>. 84 </p></dd> 85</dl></div> 86</div> 87<div class="refsect1"> 88<a name="id-1.3.49.3.7.8"></a><h2>Valid expressions</h2> 89<div class="informaltable"><table class="table"> 90<colgroup> 91<col> 92<col> 93<col> 94<col> 95<col> 96<col> 97</colgroup> 98<thead><tr> 99<th>Name</th> 100<th>Expression</th> 101<th>Type</th> 102<th>Precondition</th> 103<th>Semantics</th> 104<th>Postcondition</th> 105</tr></thead> 106<tbody> 107<tr> 108<td><p>Dereference</p></td> 109<td><p>*i</p></td> 110<td><p><span class="type">const-if-not-mutable value_type &</span></p></td> 111<td><p><code class="computeroutput">i</code> is incrementable (not 112 off-the-end)</p></td> 113<td> </td> 114<td> </td> 115</tr> 116<tr> 117<td><p>Member access</p></td> 118<td><p>i->{member-name} (return type is pointer-to-object type)</p></td> 119<td><p><span class="type">const-if-not-mutable value_type *</span></p></td> 120<td><p><code class="computeroutput">i</code> is incrementable (not 121 off-the-end)</p></td> 122<td> </td> 123<td> </td> 124</tr> 125<tr> 126<td><p>Preincrement</p></td> 127<td><p>++i</p></td> 128<td><p><span class="type">Iter &</span></p></td> 129<td><p><code class="computeroutput">i</code> is incrementable (not 130 off-the-end)</p></td> 131<td> </td> 132<td> </td> 133</tr> 134<tr> 135<td><p>Postincrement</p></td> 136<td><p>i++</p></td> 137<td><p><span class="type">Iter</span></p></td> 138<td><p><code class="computeroutput">i</code> is incrementable (not 139 off-the-end)</p></td> 140<td><p>Equivalent to <code class="computeroutput">{Iter j = i; ++i; return j;}</code></p></td> 141<td><p><code class="computeroutput">i</code> is dereferenceable or 142 off-the-end</p></td> 143</tr> 144</tbody> 145</table></div> 146</div> 147<div class="refsect1"> 148<a name="id-1.3.49.3.7.9"></a><h2>Complexity</h2> 149<p> 150 All iterator operations must take amortized constant time. 151 </p> 152</div> 153<div class="refsect1"> 154<a name="id-1.3.49.3.7.10"></a><h2>Invariants</h2> 155<div class="variablelist"><dl class="variablelist"> 156<dt><span class="term">Predecrement must return object</span></dt> 157<dd><p> 158 <code class="computeroutput">&i = &(++i)</code> 159 </p></dd> 160<dt><span class="term">Unique path through sequence</span></dt> 161<dd><p> 162 <code class="computeroutput">i == j</code> implies <code class="computeroutput">++i == ++j</code> 163 </p></dd> 164</dl></div> 165</div> 166<div class="refsect1"> 167<a name="id-1.3.49.3.7.11"></a><h2>Models</h2> 168<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 169<li class="listitem"><span class="simplelist"><span class="type">T *</span></span></li> 170<li class="listitem"><span class="simplelist"><span class="type">std::hash_set<T>::iterator</span></span></li> 171</ul></div> 172</div> 173</div> 174<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 175<td align="left"></td> 176<td align="right"><div class="copyright-footer">Copyright © 2001, 2002 Indiana University<br>Copyright © 2000, 2001 University of Notre Dame du Lac<br>Copyright © 2000 Jeremy Siek, Lie-Quan Lee, Andrew Lumsdaine<br>Copyright © 1996-1999 Silicon Graphics Computer Systems, Inc.<br>Copyright © 1994 Hewlett-Packard Company<p>Distributed under the Boost Software License, Version 1.0. 177 (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at 178 <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 179 </p> 180<p>This product includes software developed at the University 181 of Notre Dame and the Pervasive Technology Labs at Indiana 182 University. For technical information contact Andrew Lumsdaine 183 at the Pervasive Technology Labs at Indiana University. For 184 administrative and license questions contact the Advanced 185 Research and Technology Institute at 351 West 10th Street. 186 Indianapolis, Indiana 46202, phone 317-278-4100, fax 187 317-274-5902.</p> 188<p>Some concepts based on versions from the MTL draft manual 189 and Boost Graph and Property Map documentation, the SGI Standard 190 Template Library documentation and the Hewlett-Packard STL, 191 under the following license: 192 </p> 193<div class="blockquote"><blockquote class="blockquote"><p>Permission to use, copy, modify, distribute and 194 sell this software and its documentation for any purpose is 195 hereby granted without fee, provided that the above copyright 196 notice appears in all copies and that both that copyright 197 notice and this permission notice appear in supporting 198 documentation. Silicon Graphics makes no representations 199 about the suitability of this software for any purpose. It is 200 provided "as is" without express or implied 201 warranty.</p></blockquote></div> 202</div></td> 203</tr></table> 204<hr> 205<div class="spirit-nav"> 206<a accesskey="p" href="OutputIterator.html"><img src="../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="concept_check.html#concepts.reference"><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="BidirectionalIterator.html"><img src="../../doc/src/images/next.png" alt="Next"></a> 207</div> 208</body> 209</html> 210
