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  27 <div class="refnamediv">
  28 <h2><span class="refentrytitle">Concept ForwardIterator</span></h2>
  29 <p>ForwardIterator</p>
  30 </div>
  31 <div class="refsect1">
  32 <a name="idm45853365460000"></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">
  43 <a name="idm45853365458224"></a><h2>Refinement of</h2>
  44 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  45 <li class="listitem"><p><a class="link" href="InputIterator.html" title="Concept InputIterator">InputIterator</a></p></li>
  46 <li class="listitem"><p><a class="link" href="OutputIterator.html" title="Concept OutputIterator">OutputIterator</a></p></li>
  47 </ul></div>
  48 </div>
  49 <div class="refsect1">
  50 <a name="idm45853365456208"></a><h2>Associated types</h2>
  51 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  52 <li class="listitem">
  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 class="listitem">
  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">
  65 <a name="idm45853365452064"></a><h2>Notation</h2>
  66 <div class="variablelist"><dl class="variablelist">
  67 <dt><span class="term">Iter</span></dt>
  68 <dd>A type playing the role of iterator-type in the <a class="link" 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">
  78 <a name="idm45853365447984"></a><h2>Type expressions</h2>
  79 <div class="variablelist"><dl class="variablelist">
  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">
  87 <a name="idm45853365446064"></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>&#160;</td>
 113 <td>&#160;</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>&#160;</td>
 122 <td>&#160;</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>&#160;</td>
 131 <td>&#160;</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">
 147 <a name="idm45853365431440"></a><h2>Complexity</h2>
 148 <p>
 149   All iterator operations must take amortized constant time.
 150   </p>
 151 </div>
 152 <div class="refsect1">
 153 <a name="idm45853365430800"></a><h2>Invariants</h2>
 154 <div class="variablelist"><dl class="variablelist">
 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">
 166 <a name="idm45853365426880"></a><h2>Models</h2>
 167 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 168 <li class="listitem"><span class="simplelist"><span class="type">T *</span></span></li>
 169 <li class="listitem"><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">
 173 <a name="idm45853365424608"></a><h2>See also</h2>
 174 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><a class="link" href="BidirectionalIterator.html" title="Concept BidirectionalIterator">BidirectionalIterator</a></p></li></ul></div>
 175 </div>
 176 </div>
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