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<title>Concept RandomAccessIterator</title>
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<div class="refentry">
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<a name="RandomAccessIterator"></a><div class="titlepage"></div>
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<div class="refnamediv">
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<h2><span class="refentrytitle">Concept RandomAccessIterator</span></h2>
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<p>RandomAccessIterator</p>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.3"></a><h2>Description</h2>
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<p>A random access iterator is an iterator that can read through
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a sequence of values. It can move in either direction through the
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sequence (by any amount in constant time), and can be either mutable
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(data pointed to by it can be changed) or not mutable.</p>
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<p>An iterator represents a position in a sequence. Therefore,
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the iterator can point into the sequence (returning a value when
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dereferenced and being incrementable), or be off-the-end (and not
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dereferenceable or incrementable).</p>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.4"></a><h2>Refinement of</h2>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem"><p><a class="link" href="BidirectionalIterator.html" title="Concept BidirectionalIterator">BidirectionalIterator</a></p></li>
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<li class="listitem"><p><a class="link" href="LessThanComparable.html" title="Concept LessThanComparable">LessThanComparable</a></p></li>
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</ul></div>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.5"></a><h2>Associated types</h2>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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<p><span class="bold"><strong>value_type</strong></span></p>
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<pre class="literallayout">std::iterator_traits<Iter>::value_type</pre>
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<p>The value type of the iterator</p>
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</li>
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<li class="listitem">
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<p><span class="bold"><strong>category</strong></span></p>
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<pre class="literallayout">std::iterator_traits<Iter>::iterator_category</pre>
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<p>The category of the iterator</p>
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</li>
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<li class="listitem">
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<p><span class="bold"><strong>difference_type</strong></span></p>
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<pre class="literallayout">std::iterator_traits<Iter>::difference_type</pre>
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<p>The difference type of the iterator (measure of the number
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of steps between two iterators)</p>
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</li>
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</ul></div>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.6"></a><h2>Notation</h2>
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<div class="variablelist"><dl class="variablelist">
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<dt><span class="term">Iter</span></dt>
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<dd>A type playing the role of iterator-type in the <a class="link" href="RandomAccessIterator.html" title="Concept RandomAccessIterator">RandomAccessIterator</a> concept.</dd>
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<dt>
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<span class="term"><code class="varname">i</code>, </span><span class="term"><code class="varname">j</code></span>
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</dt>
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<dd>Objects of type Iter</dd>
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<dt><span class="term"><code class="varname">x</code></span></dt>
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<dd>Object of type value_type</dd>
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<dt><span class="term"><code class="varname">n</code></span></dt>
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<dd>Object of type difference_type</dd>
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<dt><span class="term"><code class="varname">int_off</code></span></dt>
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<dd>Object of type int</dd>
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</dl></div>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.7"></a><h2>Type expressions</h2>
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<div class="variablelist"><dl class="variablelist">
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<dt><span class="term">Category tag</span></dt>
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<dd><p><span class="type">category</span> must be
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derived from <span class="type">std::random_access_iterator_tag</span>.
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</p></dd>
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</dl></div>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.8"></a><h2>Valid expressions</h2>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>Name</th>
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<th>Expression</th>
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<th>Type</th>
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<th>Semantics</th>
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</tr></thead>
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<tbody>
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<tr>
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<td><p>Motion</p></td>
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<td><p>i += n</p></td>
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<td><p><span class="type">Iter &</span></p></td>
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<td><p>Equivalent to applying <code class="computeroutput">i++</code> <code class="computeroutput">n</code> times
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if <code class="computeroutput">n</code> is positive, applying <code class="computeroutput">i--</code>
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<code class="computeroutput">-n</code> times if <code class="computeroutput">n</code> is negative, and to a null
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operation if <code class="computeroutput">n</code> is zero.</p></td>
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</tr>
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<tr>
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<td><p>Motion (with integer offset)</p></td>
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<td><p>i += int_off</p></td>
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<td><p><span class="type">Iter &</span></p></td>
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<td><p>Equivalent to applying <code class="computeroutput">i++</code> <code class="computeroutput">n</code> times
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if <code class="computeroutput">n</code> is positive, applying <code class="computeroutput">i--</code>
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<code class="computeroutput">-n</code> times if <code class="computeroutput">n</code> is negative, and to a null
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operation if <code class="computeroutput">n</code> is zero.</p></td>
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</tr>
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<tr>
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<td><p>Subtractive motion</p></td>
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<td><p>i -= n</p></td>
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<td><p><span class="type">Iter &</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">i+=(-n)</code></p></td>
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</tr>
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<tr>
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<td><p>Subtractive motion (with integer offset)</p></td>
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<td><p>i -= int_off</p></td>
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<td><p><span class="type">Iter &</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">i+=(-n)</code></p></td>
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</tr>
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<tr>
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<td><p>Addition</p></td>
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<td><p>i + n</p></td>
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<td><p><span class="type">Iter</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">{Iter j = i; j += n; return j;}</code></p></td>
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</tr>
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<tr>
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<td><p>Addition with integer</p></td>
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<td><p>i + int_off</p></td>
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<td><p><span class="type">Iter</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">{Iter j = i; j += n; return j;}</code></p></td>
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</tr>
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<tr>
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<td><p>Addition (count first)</p></td>
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<td><p>n + i</p></td>
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<td><p><span class="type">Iter</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">i + n</code></p></td>
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</tr>
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<tr>
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<td><p>Addition with integer (count first)</p></td>
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<td><p>int_off + i</p></td>
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<td><p><span class="type">Iter</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">i + n</code></p></td>
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</tr>
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<tr>
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<td><p>Subtraction</p></td>
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<td><p>i - n</p></td>
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<td><p><span class="type">Iter</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">i + (-n)</code></p></td>
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</tr>
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<tr>
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<td><p>Subtraction with integer</p></td>
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<td><p>i - int_off</p></td>
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<td><p><span class="type">Iter</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">i + (-n)</code></p></td>
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</tr>
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<tr>
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<td><p>Distance</p></td>
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<td><p>i - j</p></td>
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<td><p><span class="type">difference_type</span></p></td>
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<td><p>The number of times <code class="computeroutput">i</code> must be incremented (or
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decremented if the result is negative) to reach <code class="computeroutput">j</code>. Not
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defined if <code class="computeroutput">j</code> is not reachable from
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<code class="computeroutput">i</code>.</p></td>
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</tr>
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<tr>
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<td><p>Element access</p></td>
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<td><p>i[n]</p></td>
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<td><p><span class="type">const-if-not-mutable value_type &</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">*(i + n)</code></p></td>
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</tr>
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<tr>
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<td><p>Element access with integer index</p></td>
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<td><p>i[int_off]</p></td>
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<td><p><span class="type">const-if-not-mutable value_type &</span></p></td>
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<td><p>Equivalent to <code class="computeroutput">*(i + n)</code></p></td>
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</tr>
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</tbody>
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</table></div>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.9"></a><h2>Complexity</h2>
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<p>
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All iterator operations must take amortized constant time.
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</p>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.10"></a><h2>Models</h2>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem"><span class="simplelist"><span class="type">T *</span></span></li>
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<li class="listitem"><span class="simplelist"><span class="type">std::vector<T>::iterator</span></span></li>
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<li class="listitem"><span class="simplelist"><span class="type">std::vector<T>::const_iterator</span></span></li>
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<li class="listitem"><span class="simplelist"><span class="type">std::deque<T>::iterator</span></span></li>
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<li class="listitem"><span class="simplelist"><span class="type">std::deque<T>::const_iterator</span></span></li>
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</ul></div>
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</div>
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<div class="refsect1">
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<a name="id-1.3.50.3.9.11"></a><h2>See also</h2>
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<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>
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</div>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<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.
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(See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at
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<a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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</p>
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<p>This product includes software developed at the University
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of Notre Dame and the Pervasive Technology Labs at Indiana
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University. For technical information contact Andrew Lumsdaine
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at the Pervasive Technology Labs at Indiana University. For
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administrative and license questions contact the Advanced
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Research and Technology Institute at 351 West 10th Street.
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Indianapolis, Indiana 46202, phone 317-278-4100, fax
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317-274-5902.</p>
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<p>Some concepts based on versions from the MTL draft manual
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and Boost Graph and Property Map documentation, the SGI Standard
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Template Library documentation and the Hewlett-Packard STL,
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under the following license:
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</p>
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<div class="blockquote"><blockquote class="blockquote"><p>Permission to use, copy, modify, distribute and
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sell this software and its documentation for any purpose is
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hereby granted without fee, provided that the above copyright
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notice appears in all copies and that both that copyright
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notice and this permission notice appear in supporting
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documentation. Silicon Graphics makes no representations
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about the suitability of this software for any purpose. It is
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provided "as is" without express or implied
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warranty.</p></blockquote></div>
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</tr></table>
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