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4<title>Concept ForwardIterator</title>
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25<div class="refentry" lang="en">
26<a name="ForwardIterator"></a><div class="titlepage"></div>
27<div class="refnamediv">
28<h2><span class="refentrytitle">Concept ForwardIterator</span></h2>
29<p>ForwardIterator</p>
30</div>
31<div class="refsect1" lang="en">
32<a name="id943468"></a><h2>Description</h2>
33<p>A forward iterator is an iterator that can read through a sequence of
34  values.  It is multi-pass (old values of the iterator can be
35  re-used), and can be either mutable (data pointed to by it can be
36  changed) or not mutable.</p>
37<p>An iterator represents a position in a sequence.  Therefore, the
38  iterator can point into the sequence (returning a value when dereferenced
39  and being incrementable), or be off-the-end (and not dereferenceable or
40  incrementable).</p>
41</div>
42<div class="refsect1" lang="en">
43<a name="id943487"></a><h2>Refinement of</h2>
44<div class="itemizedlist"><ul type="disc">
45<li><p><a href="InputIterator.html" title="Concept InputIterator">InputIterator</a></p></li>
46<li><p><a href="OutputIterator.html" title="Concept OutputIterator">OutputIterator</a></p></li>
47</ul></div>
48</div>
49<div class="refsect1" lang="en">
50<a name="id943507"></a><h2>Associated types</h2>
51<div class="itemizedlist"><ul type="disc">
52<li>
53<p><span class="bold"><strong>value_type</strong></span></p>
54<pre class="literallayout">std::iterator_traits&lt;Iter&gt;::value_type</pre>
55<p>The value type of the iterator</p>
56</li>
57<li>
58<p><span class="bold"><strong>category</strong></span></p>
59<pre class="literallayout">std::iterator_traits&lt;Iter&gt;::iterator_category</pre>
60<p>The category of the iterator</p>
61</li>
62</ul></div>
63</div>
64<div class="refsect1" lang="en">
65<a name="id943547"></a><h2>Notation</h2>
66<div class="variablelist"><dl>
67<dt><span class="term">Iter</span></dt>
68<dd>A type playing the role of iterator-type in the <a href="ForwardIterator.html" title="Concept ForwardIterator">ForwardIterator</a> concept.</dd>
69<dt>
70<span class="term"><code class="varname">i</code>, </span><span class="term"><code class="varname">j</code></span>
71</dt>
72<dd>Objects of type Iter</dd>
73<dt><span class="term"><code class="varname">x</code></span></dt>
74<dd>Object of type value_type</dd>
75</dl></div>
76</div>
77<div class="refsect1" lang="en">
78<a name="id943585"></a><h2>Type expressions</h2>
79<div class="variablelist"><dl>
80<dt><span class="term">Category tag</span></dt>
81<dd><p><span class="type">category</span> must be
82                  derived from <span class="type">std::forward_iterator_tag</span>.
83                </p></dd>
84</dl></div>
85</div>
86<div class="refsect1" lang="en">
87<a name="id943604"></a><h2>Valid expressions</h2>
88<div class="informaltable"><table class="table">
89<colgroup>
90<col>
91<col>
92<col>
93<col>
94<col>
95<col>
96</colgroup>
97<thead><tr>
98<th>Name</th>
99<th>Expression</th>
100<th>Type</th>
101<th>Precondition</th>
102<th>Semantics</th>
103<th>Postcondition</th>
104</tr></thead>
105<tbody>
106<tr>
107<td><p>Dereference</p></td>
108<td><p>*i</p></td>
109<td><p><span class="type">const-if-not-mutable value_type &amp;</span></p></td>
110<td><p><code class="computeroutput">i</code> is incrementable (not
111    off-the-end)</p></td>
112<td> </td>
113<td> </td>
114</tr>
115<tr>
116<td><p>Member access</p></td>
117<td><p>i-&gt;{member-name} (return type is pointer-to-object type)</p></td>
118<td><p><span class="type">const-if-not-mutable value_type *</span></p></td>
119<td><p><code class="computeroutput">i</code> is incrementable (not
120    off-the-end)</p></td>
121<td> </td>
122<td> </td>
123</tr>
124<tr>
125<td><p>Preincrement</p></td>
126<td><p>++i</p></td>
127<td><p><span class="type">Iter &amp;</span></p></td>
128<td><p><code class="computeroutput">i</code> is incrementable (not
129    off-the-end)</p></td>
130<td> </td>
131<td> </td>
132</tr>
133<tr>
134<td><p>Postincrement</p></td>
135<td><p>i++</p></td>
136<td><p><span class="type">Iter</span></p></td>
137<td><p><code class="computeroutput">i</code> is incrementable (not
138    off-the-end)</p></td>
139<td><p>Equivalent to <code class="computeroutput">{Iter j = i; ++i; return j;}</code></p></td>
140<td><p><code class="computeroutput">i</code> is dereferenceable or
141    off-the-end</p></td>
142</tr>
143</tbody>
144</table></div>
145</div>
146<div class="refsect1" lang="en">
147<a name="id961214"></a><h2>Complexity</h2>
148<p>
149  All iterator operations must take amortized constant time.
150  </p>
151</div>
152<div class="refsect1" lang="en">
153<a name="id961221"></a><h2>Invariants</h2>
154<div class="variablelist"><dl>
155<dt><span class="term">Predecrement must return object</span></dt>
156<dd><p>
157  <code class="computeroutput">&amp;i = &amp;(++i)</code>
158  </p></dd>
159<dt><span class="term">Unique path through sequence</span></dt>
160<dd><p>
161  <code class="computeroutput">i == j</code> implies <code class="computeroutput">++i == ++j</code>
162  </p></dd>
163</dl></div>
164</div>
165<div class="refsect1" lang="en">
166<a name="id961257"></a><h2>Models</h2>
167<div class="itemizedlist"><ul type="disc">
168<li><span class="simplelist"><span class="type">T *</span></span></li>
169<li><span class="simplelist"><span class="type">std::hash_set&lt;T&gt;::iterator</span></span></li>
170</ul></div>
171</div>
172<div class="refsect1" lang="en">
173<a name="id961277"></a><h2>See also</h2>
174<div class="itemizedlist"><ul type="disc"><li><p><a href="BidirectionalIterator.html" title="Concept BidirectionalIterator">BidirectionalIterator</a></p></li></ul></div>
175</div>
176</div>
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179<td align="right"><small>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</small></td>
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