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Dave Abrahams
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<title>Counting Iterator</title>
<meta name="author" content="David Abrahams, Jeremy Siek, Thomas Witt" />
<meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" />
<meta name="date" content="2004-01-12" />
<meta name="date" content="2004-01-13" />
<meta name="copyright" content="Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved" />
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@ -27,7 +27,7 @@
Lab</a>, University of Hanover <a class="last reference" href="http://www.ive.uni-hannover.de">Institute for Transport
Railway Operation and Construction</a></td></tr>
<tr><th class="docinfo-name">Date:</th>
<td>2004-01-12</td></tr>
<td>2004-01-13</td></tr>
<tr><th class="docinfo-name">Copyright:</th>
<td>Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved</td></tr>
</tbody>
@ -36,21 +36,21 @@ Railway Operation and Construction</a></td></tr>
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">abstract:</th><td class="field-body">How would you fill up a vector with the numbers zero
<tr class="field"><th class="field-name">abstract:</th><td class="field-body"><p class="first">How would you fill up a vector with the numbers zero
through one hundred using <tt class="literal"><span class="pre">std::copy()</span></tt>? The only iterator
operation missing from builtin integer types is an
<tt class="literal"><span class="pre">operator*()</span></tt> that returns the current value of the integer.
The counting iterator adaptor adds this crucial piece of
functionality to whatever type it wraps. One can use the
counting iterator adaptor not only with integer types, but with
any type that is <strong>Incrementable</strong> (see type requirements
below).</td>
any incrementable type.</p>
<p class="last"><tt class="literal"><span class="pre">counting_iterator</span></tt> adapts an object by adding an <tt class="literal"><span class="pre">operator*</span></tt> that
returns the current value of the object. All other iterator operations
are forwarded to the adapted object.</p>
</td>
</tr>
</tbody>
</table>
<p><tt class="literal"><span class="pre">counting_iterator</span></tt> adapts an object by adding an <tt class="literal"><span class="pre">operator*</span></tt> that
returns the current value of the object. All other iterator operations
are forwarded to the adapted object.</p>
<div class="contents topic" id="table-of-contents">
<p class="topic-title"><a name="table-of-contents">Table of Contents</a></p>
<ul class="simple">
@ -90,53 +90,53 @@ class counting_iterator
};
</pre>
<p>If the <tt class="literal"><span class="pre">Difference</span></tt> argument is <tt class="literal"><span class="pre">use_default</span></tt> then the
<tt class="literal"><span class="pre">difference_type</span></tt> member is an implementation defined signed
integral type. Otherwise <tt class="literal"><span class="pre">difference_type</span></tt> is <tt class="literal"><span class="pre">Difference</span></tt>.</p>
<tt class="literal"><span class="pre">difference_type</span></tt> member is an unspecified signed integral
type. Otherwise <tt class="literal"><span class="pre">difference_type</span></tt> is <tt class="literal"><span class="pre">Difference</span></tt>.</p>
<p>If <tt class="literal"><span class="pre">CategoryOrTraversal</span></tt> is not <tt class="literal"><span class="pre">use_default</span></tt> then the member
<tt class="literal"><span class="pre">iterator_category</span></tt> is <tt class="literal"><span class="pre">CategoryOrTraversal</span></tt>. Otherwise, if
<tt class="literal"><span class="pre">Incrementable</span></tt> is a numeric type then <tt class="literal"><span class="pre">iterator_category</span></tt> is a
type convertible to <tt class="literal"><span class="pre">random_access_iterator_tag</span></tt>. If
<tt class="literal"><span class="pre">Incrementable</span></tt> is not a numeric type then <tt class="literal"><span class="pre">iterator_category</span></tt> is
<tt class="literal"><span class="pre">iterator_traversal&lt;Incrementable&gt;::type</span></tt>.</p>
<tt class="literal"><span class="pre">Incrementable</span></tt> is a numberic type <tt class="literal"><span class="pre">iterator_category</span></tt> is a
type convertible to <tt class="literal"><span class="pre">random_access_iterator_tag</span></tt>. Otherwise,
<tt class="literal"><span class="pre">iterator_category</span></tt> is unspecified, and the <tt class="literal"><span class="pre">counting_iterator</span></tt>
specialization models the same iterator traversal concepts modeled
by <tt class="literal"><span class="pre">Incrementable</span></tt>.</p>
<dl>
<dt>[<em>Note:</em> implementers are encouraged to provide an implementation of</dt>
<dd><tt class="literal"><span class="pre">operator-</span></tt> and a <tt class="literal"><span class="pre">difference_type</span></tt> that avoids overflows in
<dd><tt class="literal"><span class="pre">operator-</span></tt> and a <tt class="literal"><span class="pre">difference_type</span></tt> that avoid overflows in
the cases when the <tt class="literal"><span class="pre">Incrementable</span></tt> type is a numeric type.]</dd>
</dl>
</div>
<div class="section" id="counting-iterator-requirements">
<h1><a class="toc-backref" href="#id3" name="counting-iterator-requirements"><tt class="literal"><span class="pre">counting_iterator</span></tt> requirements</a></h1>
<p>The <tt class="literal"><span class="pre">Incrementable</span></tt> type must be Default Constructible, Copy
<p><tt class="literal"><span class="pre">Incrementable</span></tt> must be Default Constructible, Copy
Constructible, and Assignable.</p>
<p>If <tt class="literal"><span class="pre">iterator_category</span></tt> is convertible to <tt class="literal"><span class="pre">forward_iterator_tag</span></tt> or
<tt class="literal"><span class="pre">forward_traversal_tag</span></tt> then the following expressions must be valid:</p>
<p>If <tt class="literal"><span class="pre">iterator_category</span></tt> is convertible to <tt class="literal"><span class="pre">forward_iterator_tag</span></tt>
or <tt class="literal"><span class="pre">forward_traversal_tag</span></tt>, the following must be well-formed:</p>
<pre class="literal-block">
Incrementable i, j;
++i // pre-increment
i == j // operator equal
++i; // pre-increment
i == j; // operator equal
</pre>
<p>If <tt class="literal"><span class="pre">iterator_category</span></tt> is convertible to
<tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt> or <tt class="literal"><span class="pre">bidirectional_traversal_tag</span></tt> then
pre-decrement is required:</p>
<tt class="literal"><span class="pre">bidirectional_iterator_tag</span></tt> or <tt class="literal"><span class="pre">bidirectional_traversal_tag</span></tt>,
the following expression must also be well-formed:</p>
<pre class="literal-block">
--i
</pre>
<p>If <tt class="literal"><span class="pre">iterator_category</span></tt> is convertible to
<tt class="literal"><span class="pre">random_access_iterator_tag</span></tt> or <tt class="literal"><span class="pre">random_access_traversal_tag</span></tt> then
these additional expressions are also required:</p>
<tt class="literal"><span class="pre">random_access_iterator_tag</span></tt> or <tt class="literal"><span class="pre">random_access_traversal_tag</span></tt>,
the following must must also be valid:</p>
<pre class="literal-block">
counting_iterator::difference_type n;
i += n
n = i - j
i &lt; j
i += n;
n = i - j;
i &lt; j;
</pre>
</div>
<div class="section" id="counting-iterator-models">
<h1><a class="toc-backref" href="#id4" name="counting-iterator-models"><tt class="literal"><span class="pre">counting_iterator</span></tt> models</a></h1>
<p><tt class="literal"><span class="pre">counting_iterator</span></tt> models Readable Lvalue Iterator. In addition,
<tt class="literal"><span class="pre">counting_iterator</span></tt> models the concepts corresponding to the
iterator tags that <tt class="literal"><span class="pre">counting_iterator::iterator_category</span></tt> is
convertible to.</p>
<p>Specializations of <tt class="literal"><span class="pre">counting_iterator</span></tt> model Readable Lvalue
Iterator. In addition, they model the concepts corresponding to the
iterator tags to which their <tt class="literal"><span class="pre">iterator_category</span></tt> is convertible.</p>
</div>
<div class="section" id="counting-iterator-operations">
<h1><a class="toc-backref" href="#id5" name="counting-iterator-operations"><tt class="literal"><span class="pre">counting_iterator</span></tt> operations</a></h1>
@ -258,10 +258,10 @@ indirectly printing out the numbers from 0 to 7
<p>The source code for this example can be found <a class="reference" href="../example/counting_iterator_example.cpp">here</a>.</p>
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