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  26 <a name="RandomAccessIterator"></a><div class="titlepage"></div>
  27 <div class="refnamediv">
  28 <h2><span class="refentrytitle">Concept RandomAccessIterator</span></h2>
  29 <p>RandomAccessIterator</p>
  30 </div>
  31 <div class="refsect1">
  32 <a name="idm45853365385488"></a><h2>Description</h2>
  33 <p>A random access iterator is an iterator that can read through
  34   a sequence of values.  It can move in either direction through the
  35   sequence (by any amount in constant time), and can be either mutable
  36   (data pointed to by it can be changed) or not mutable.</p>
  37 <p>An iterator represents a position in a sequence.  Therefore,
  38   the iterator can point into the sequence (returning a value when
  39   dereferenced and being incrementable), or be off-the-end (and not
  40   dereferenceable or incrementable).</p>
  41 </div>
  42 <div class="refsect1">
  43 <a name="idm45853365383680"></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="BidirectionalIterator.html" title="Concept BidirectionalIterator">BidirectionalIterator</a></p></li>
  46 <li class="listitem"><p><a class="link" href="LessThanComparable.html" title="Concept LessThanComparable">LessThanComparable</a></p></li>
  47 </ul></div>
  48 </div>
  49 <div class="refsect1">
  50 <a name="idm45853365381664"></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 <li class="listitem">
  63 <p><span class="bold"><strong>difference_type</strong></span></p>
  64 <pre class="literallayout">std::iterator_traits&lt;Iter&gt;::difference_type</pre>
  65 <p>The difference type of the iterator (measure of the number
  66     of steps between two iterators)</p>
  67 </li>
  68 </ul></div>
  69 </div>
  70 <div class="refsect1">
  71 <a name="idm45853365375664"></a><h2>Notation</h2>
  72 <div class="variablelist"><dl class="variablelist">
  73 <dt><span class="term">Iter</span></dt>
  74 <dd>A type playing the role of iterator-type in the <a class="link" href="RandomAccessIterator.html" title="Concept RandomAccessIterator">RandomAccessIterator</a> concept.</dd>
  75 <dt>
  76 <span class="term"><code class="varname">i</code>, </span><span class="term"><code class="varname">j</code></span>
  77 </dt>
  78 <dd>Objects of type Iter</dd>
  79 <dt><span class="term"><code class="varname">x</code></span></dt>
  80 <dd>Object of type value_type</dd>
  81 <dt><span class="term"><code class="varname">n</code></span></dt>
  82 <dd>Object of type difference_type</dd>
  83 <dt><span class="term"><code class="varname">int_off</code></span></dt>
  84 <dd>Object of type int</dd>
  85 </dl></div>
  86 </div>
  87 <div class="refsect1">
  88 <a name="idm45853365369792"></a><h2>Type expressions</h2>
  89 <div class="variablelist"><dl class="variablelist">
  90 <dt><span class="term">Category tag</span></dt>
  91 <dd><p><span class="type">category</span> must be
  92                   derived from <span class="type">std::random_access_iterator_tag</span>.
  93                 </p></dd>
  94 </dl></div>
  95 </div>
  96 <div class="refsect1">
  97 <a name="idm45853365367872"></a><h2>Valid expressions</h2>
  98 <div class="informaltable"><table class="table">
  99 <colgroup>
 100 <col>
 101 <col>
 102 <col>
 103 <col>
 104 </colgroup>
 105 <thead><tr>
 106 <th>Name</th>
 107 <th>Expression</th>
 108 <th>Type</th>
 109 <th>Semantics</th>
 110 </tr></thead>
 111 <tbody>
 112 <tr>
 113 <td><p>Motion</p></td>
 114 <td><p>i += n</p></td>
 115 <td><p><span class="type">Iter &amp;</span></p></td>
 116 <td><p>Equivalent to applying <code class="computeroutput">i++</code> <code class="computeroutput">n</code> times
 117     if <code class="computeroutput">n</code> is positive, applying <code class="computeroutput">i--</code>
 118     <code class="computeroutput">-n</code> times if <code class="computeroutput">n</code> is negative, and to a null
 119     operation if <code class="computeroutput">n</code> is zero.</p></td>
 120 </tr>
 121 <tr>
 122 <td><p>Motion (with integer offset)</p></td>
 123 <td><p>i += int_off</p></td>
 124 <td><p><span class="type">Iter &amp;</span></p></td>
 125 <td><p>Equivalent to applying <code class="computeroutput">i++</code> <code class="computeroutput">n</code> times
 126     if <code class="computeroutput">n</code> is positive, applying <code class="computeroutput">i--</code>
 127     <code class="computeroutput">-n</code> times if <code class="computeroutput">n</code> is negative, and to a null
 128     operation if <code class="computeroutput">n</code> is zero.</p></td>
 129 </tr>
 130 <tr>
 131 <td><p>Subtractive motion</p></td>
 132 <td><p>i -= n</p></td>
 133 <td><p><span class="type">Iter &amp;</span></p></td>
 134 <td><p>Equivalent to <code class="computeroutput">i+=(-n)</code></p></td>
 135 </tr>
 136 <tr>
 137 <td><p>Subtractive motion (with integer offset)</p></td>
 138 <td><p>i -= int_off</p></td>
 139 <td><p><span class="type">Iter &amp;</span></p></td>
 140 <td><p>Equivalent to <code class="computeroutput">i+=(-n)</code></p></td>
 141 </tr>
 142 <tr>
 143 <td><p>Addition</p></td>
 144 <td><p>i + n</p></td>
 145 <td><p><span class="type">Iter</span></p></td>
 146 <td><p>Equivalent to <code class="computeroutput">{Iter j = i; j += n; return j;}</code></p></td>
 147 </tr>
 148 <tr>
 149 <td><p>Addition with integer</p></td>
 150 <td><p>i + int_off</p></td>
 151 <td><p><span class="type">Iter</span></p></td>
 152 <td><p>Equivalent to <code class="computeroutput">{Iter j = i; j += n; return j;}</code></p></td>
 153 </tr>
 154 <tr>
 155 <td><p>Addition (count first)</p></td>
 156 <td><p>n + i</p></td>
 157 <td><p><span class="type">Iter</span></p></td>
 158 <td><p>Equivalent to <code class="computeroutput">i + n</code></p></td>
 159 </tr>
 160 <tr>
 161 <td><p>Addition with integer (count first)</p></td>
 162 <td><p>int_off + i</p></td>
 163 <td><p><span class="type">Iter</span></p></td>
 164 <td><p>Equivalent to <code class="computeroutput">i + n</code></p></td>
 165 </tr>
 166 <tr>
 167 <td><p>Subtraction</p></td>
 168 <td><p>i - n</p></td>
 169 <td><p><span class="type">Iter</span></p></td>
 170 <td><p>Equivalent to <code class="computeroutput">i + (-n)</code></p></td>
 171 </tr>
 172 <tr>
 173 <td><p>Subtraction with integer</p></td>
 174 <td><p>i - int_off</p></td>
 175 <td><p><span class="type">Iter</span></p></td>
 176 <td><p>Equivalent to <code class="computeroutput">i + (-n)</code></p></td>
 177 </tr>
 178 <tr>
 179 <td><p>Distance</p></td>
 180 <td><p>i - j</p></td>
 181 <td><p><span class="type">difference_type</span></p></td>
 182 <td><p>The number of times <code class="computeroutput">i</code> must be incremented (or
 183     decremented if the result is negative) to reach <code class="computeroutput">j</code>.  Not
 184     defined if <code class="computeroutput">j</code> is not reachable from
 185     <code class="computeroutput">i</code>.</p></td>
 186 </tr>
 187 <tr>
 188 <td><p>Element access</p></td>
 189 <td><p>i[n]</p></td>
 190 <td><p><span class="type">const-if-not-mutable value_type &amp;</span></p></td>
 191 <td><p>Equivalent to <code class="computeroutput">*(i + n)</code></p></td>
 192 </tr>
 193 <tr>
 194 <td><p>Element access with integer index</p></td>
 195 <td><p>i[int_off]</p></td>
 196 <td><p><span class="type">const-if-not-mutable value_type &amp;</span></p></td>
 197 <td><p>Equivalent to <code class="computeroutput">*(i + n)</code></p></td>
 198 </tr>
 199 </tbody>
 200 </table></div>
 201 </div>
 202 <div class="refsect1">
 203 <a name="idm45853365325840"></a><h2>Complexity</h2>
 204 <p>
 205   All iterator operations must take amortized constant time.
 206   </p>
 207 </div>
 208 <div class="refsect1">
 209 <a name="idm45853365325120"></a><h2>Models</h2>
 210 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 211 <li class="listitem"><span class="simplelist"><span class="type">T *</span></span></li>
 212 <li class="listitem"><span class="simplelist"><span class="type">std::vector&lt;T&gt;::iterator</span></span></li>
 213 <li class="listitem"><span class="simplelist"><span class="type">std::vector&lt;T&gt;::const_iterator</span></span></li>
 214 <li class="listitem"><span class="simplelist"><span class="type">std::deque&lt;T&gt;::iterator</span></span></li>
 215 <li class="listitem"><span class="simplelist"><span class="type">std::deque&lt;T&gt;::const_iterator</span></span></li>
 216 </ul></div>
 217 </div>
 218 <div class="refsect1">
 219 <a name="idm45853365320112"></a><h2>See also</h2>
 220 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><a class="link" href="LessThanComparable.html" title="Concept LessThanComparable">LessThanComparable</a></p></li></ul></div>
 221 </div>
 222 </div>
 223 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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