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<div class="section" id="iterator-category">
<h1><a class="toc-backref" href="./iterator-metafunctions.html#id1459">iterator_category</a></h1>
<div class="section" id="id445">
<h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
<pre class="literal-block">
template&lt;
      typename Iterator
    &gt;
struct <a href="./iterator-category.html" class="identifier">iterator_category</a>
{
    typedef typename Iterator::category type;
};
</pre>
</div>
<div class="section" id="id446">
<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
<p>Returns one of the following iterator category tags:</p>
<ul class="simple">
<li><tt class="literal"><span class="pre">forward_iterator_tag</span></tt></li>
<li><tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt></li>
<li><tt class="literal"><span class="pre">random_access_iterator_tag</span></tt></li>
</ul>
</div>
<div class="section" id="id447">
<h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
<pre class="literal-block">
#include &lt;<a href="../../../../boost/mpl/iterator_category.hpp" class="header">boost/mpl/iterator_category.hpp</a>&gt;
#include &lt;<a href="../../../../boost/mpl/iterator_tags.hpp" class="header">boost/mpl/iterator_tags.hpp</a>&gt;
</pre>
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<div class="section" id="id448">
<h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
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<tr><th class="head">Parameter</th>
<th class="head">Requirement</th>
<th class="head">Description</th>
</tr>
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<tr><td><tt class="literal"><span class="pre">Iterator</span></tt></td>
<td><a class="reference internal" href="./forward-iterator.html">Forward Iterator</a></td>
<td>The iterator to obtain a category for.</td>
</tr>
</tbody>
</table>
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<div class="section" id="id449">
<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
<p>For any <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a>s <tt class="literal"><span class="pre">iter</span></tt>:</p>
<pre class="literal-block">
typedef <a href="./iterator-category.html" class="identifier">iterator_category</a>&lt;iter&gt;::type tag;
</pre>
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<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first"><a class="reference internal" href="./integral-constant.html">Integral Constant</a>.</p>
</td>
</tr>
<tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first"><tt class="literal"><span class="pre">tag</span></tt> is <tt class="literal"><span class="pre">forward_iterator_tag</span></tt> if <tt class="literal"><span class="pre">iter</span></tt> is a model of <a class="reference internal" href="./forward-iterator.html">Forward Iterator</a>,
<tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt> if <tt class="literal"><span class="pre">iter</span></tt> is a model of <a class="reference internal" href="./bidirectional-iterator.html">Bidirectional Iterator</a>,
or <tt class="literal"><span class="pre">random_access_iterator_tag</span></tt> if <tt class="literal"><span class="pre">iter</span></tt> is a model of <a class="reference internal" href="./random-access-iterator.html">Random Access Iterator</a>;</p>
</td>
</tr>
<tr class="field"><th class="field-name">Postcondition:</th><td class="field-body"><dl class="first last docutils">
<dt><tt class="literal"><span class="pre">forward_iterator_tag::value</span> <span class="pre">&lt;</span> <span class="pre">bidirectional_iterator_tag::value</span></tt>,</dt>
<dd><p class="first last"><tt class="literal"><span class="pre">bidirectional_iterator_tag::value</span> <span class="pre">&lt;</span> <span class="pre">random_access_iterator_tag::value</span></tt>.</p>
</dd>
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<div class="section" id="id450">
<h3><a class="subsection-title" href="#complexity" name="complexity">Complexity</a></h3>
<p>Amortized constant time.</p>
</div>
<div class="section" id="id451">
<h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
<pre class="literal-block">
template&lt; typename Tag, typename Iterator &gt;
struct algorithm_impl
{
    // <em>O(n)</em> implementation
};

template&lt; typename Iterator &gt;
struct algorithm_impl&lt;random_access_iterator_tag,Iterator&gt;
{
    // <em>O(1)</em> implementation
};

template&lt; typename Iterator &gt;
struct algorithm
    : algorithm_impl&lt;
          <a href="./iterator-category.html" class="identifier">iterator_category</a>&lt;Iterator&gt;::type
        , Iterator
        >
{
};
</pre>
</div>
<div class="section" id="id452">
<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
<p><a class="reference internal" href="./iterators.html">Iterators</a>, <a class="reference internal" href="./begin.html">begin</a> / <a class="reference internal" href="./end.html">end</a>, <a class="reference internal" href="./advance.html">advance</a>, <a class="reference internal" href="./distance.html">distance</a>, <a class="reference internal" href="./next.html">next</a></p>
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