Files
iterator/doc/counting_iterator.html
T

286 lines
17 KiB
HTML
Raw Normal View History

2003-08-05 19:48:41 +00:00
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
2005-05-20 15:32:55 +00:00
<meta name="generator" content="Docutils 0.3.8: http://docutils.sourceforge.net/" />
2003-08-05 19:48:41 +00:00
<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" />
2004-11-02 14:31:27 +00:00
<meta name="date" content="2004-11-01" />
<meta name="copyright" content="Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003." />
<link rel="stylesheet" href="default.css" type="text/css" />
2003-08-05 19:48:41 +00:00
</head>
<body>
2005-05-20 15:32:55 +00:00
<div class="document" id="counting-iterator">
2003-08-05 19:48:41 +00:00
<h1 class="title">Counting Iterator</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Author:</th>
<td>David Abrahams, Jeremy Siek, Thomas Witt</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first reference" href="mailto:dave&#64;boost-consulting.com">dave&#64;boost-consulting.com</a>, <a class="reference" href="mailto:jsiek&#64;osl.iu.edu">jsiek&#64;osl.iu.edu</a>, <a class="last reference" href="mailto:witt&#64;ive.uni-hannover.de">witt&#64;ive.uni-hannover.de</a></td></tr>
<tr><th class="docinfo-name">Organization:</th>
<td><a class="first reference" href="http://www.boost-consulting.com">Boost Consulting</a>, Indiana University <a class="reference" href="http://www.osl.iu.edu">Open Systems
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>
2004-11-02 14:31:27 +00:00
<td>2004-11-01</td></tr>
2003-08-05 19:48:41 +00:00
<tr><th class="docinfo-name">Copyright:</th>
2004-11-02 14:31:27 +00:00
<td>Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003.</td></tr>
2003-08-05 19:48:41 +00:00
</tbody>
</table>
2005-05-20 15:32:55 +00:00
<table class="docutils field-list" frame="void" rules="none">
2003-08-05 19:48:41 +00:00
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2004-01-13 13:36:55 +00:00
<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
2005-05-20 15:32:55 +00:00
through one hundred using <tt class="docutils literal"><span class="pre">std::copy()</span></tt>? The only iterator
2004-01-12 20:58:22 +00:00
operation missing from builtin integer types is an
2005-05-20 15:32:55 +00:00
<tt class="docutils literal"><span class="pre">operator*()</span></tt> that returns the current value of the integer.
2004-01-12 20:58:22 +00:00
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
2004-01-13 13:36:55 +00:00
any incrementable type.</p>
2005-05-20 15:32:55 +00:00
<p class="last"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> adapts an object by adding an <tt class="docutils literal"><span class="pre">operator*</span></tt> that
2004-01-13 13:36:55 +00:00
returns the current value of the object. All other iterator operations
are forwarded to the adapted object.</p>
</td>
2003-08-05 19:48:41 +00:00
</tr>
</tbody>
</table>
<div class="contents topic" id="table-of-contents">
2004-11-02 14:31:27 +00:00
<p class="topic-title first"><a name="table-of-contents">Table of Contents</a></p>
2003-08-05 19:48:41 +00:00
<ul class="simple">
2005-05-20 15:32:55 +00:00
<li><a class="reference" href="#counting-iterator-synopsis" id="id2" name="id2"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> synopsis</a></li>
<li><a class="reference" href="#counting-iterator-requirements" id="id3" name="id3"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> requirements</a></li>
<li><a class="reference" href="#counting-iterator-models" id="id4" name="id4"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models</a></li>
<li><a class="reference" href="#counting-iterator-operations" id="id5" name="id5"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> operations</a></li>
2004-01-12 16:10:29 +00:00
<li><a class="reference" href="#example" id="id6" name="id6">Example</a></li>
2003-08-05 19:48:41 +00:00
</ul>
</div>
<div class="section" id="counting-iterator-synopsis">
2005-05-20 15:32:55 +00:00
<h1><a class="toc-backref" href="#id2" name="counting-iterator-synopsis"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> synopsis</a></h1>
2003-08-05 19:48:41 +00:00
<pre class="literal-block">
template &lt;
class Incrementable
2004-01-12 00:48:21 +00:00
, class CategoryOrTraversal = use_default
, class Difference = use_default
&gt;
2003-08-05 19:48:41 +00:00
class counting_iterator
{
public:
2004-01-12 19:01:57 +00:00
typedef Incrementable value_type;
typedef const Incrementable&amp; reference;
typedef const Incrementable* pointer;
typedef /* see below */ difference_type;
typedef /* see below */ iterator_category;
2003-08-05 19:48:41 +00:00
counting_iterator();
counting_iterator(counting_iterator const&amp; rhs);
2004-01-12 00:48:21 +00:00
explicit counting_iterator(Incrementable x);
Incrementable const&amp; base() const;
reference operator*() const;
counting_iterator&amp; operator++();
counting_iterator&amp; operator--();
private:
Incrementable m_inc; // exposition
};
2003-08-05 19:48:41 +00:00
</pre>
2005-05-20 15:32:55 +00:00
<p>If the <tt class="docutils literal"><span class="pre">Difference</span></tt> argument is <tt class="docutils literal"><span class="pre">use_default</span></tt> then
<tt class="docutils literal"><span class="pre">difference_type</span></tt> is an unspecified signed integral
type. Otherwise <tt class="docutils literal"><span class="pre">difference_type</span></tt> is <tt class="docutils literal"><span class="pre">Difference</span></tt>.</p>
<p><tt class="docutils literal"><span class="pre">iterator_category</span></tt> is determined according to the following
algorithm:</p>
<pre class="literal-block">
if (CategoryOrTraversal is not use_default)
return CategoryOrTraversal
else if (numeric_limits&lt;Incrementable&gt;::is_specialized)
return <a class="reference" href="iterator_facade.html#iterator-category"><em>iterator-category</em></a>(
random_access_traversal_tag, Incrementable, const Incrementable&amp;)
else
return <a class="reference" href="iterator_facade.html#iterator-category"><em>iterator-category</em></a>(
iterator_traversal&lt;Incrementable&gt;::type,
Incrementable, const Incrementable&amp;)
</pre>
2005-05-20 15:32:55 +00:00
<dl class="docutils">
<dt>[<em>Note:</em> implementers are encouraged to provide an implementation of</dt>
2005-05-20 15:32:55 +00:00
<dd><tt class="docutils literal"><span class="pre">operator-</span></tt> and a <tt class="docutils literal"><span class="pre">difference_type</span></tt> that avoids overflows in
the cases where <tt class="docutils literal"><span class="pre">std::numeric_limits&lt;Incrementable&gt;::is_specialized</span></tt>
is true.]</dd>
</dl>
</div>
2003-08-05 19:48:41 +00:00
<div class="section" id="counting-iterator-requirements">
2005-05-20 15:32:55 +00:00
<h1><a class="toc-backref" href="#id3" name="counting-iterator-requirements"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> requirements</a></h1>
<p>The <tt class="docutils literal"><span class="pre">Incrementable</span></tt> argument shall be Copy Constructible and Assignable.</p>
<p>If <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to <tt class="docutils literal"><span class="pre">forward_iterator_tag</span></tt>
or <tt class="docutils literal"><span class="pre">forward_traversal_tag</span></tt>, the following must be well-formed:</p>
2003-08-05 19:48:41 +00:00
<pre class="literal-block">
Incrementable i, j;
2004-01-13 13:36:55 +00:00
++i; // pre-increment
i == j; // operator equal
2003-08-05 19:48:41 +00:00
</pre>
2005-05-20 15:32:55 +00:00
<p>If <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
<tt class="docutils literal"><span class="pre">bidirectional_iterator_tag</span></tt> or <tt class="docutils literal"><span class="pre">bidirectional_traversal_tag</span></tt>,
2004-01-13 13:36:55 +00:00
the following expression must also be well-formed:</p>
2003-08-05 19:48:41 +00:00
<pre class="literal-block">
--i
</pre>
2005-05-20 15:32:55 +00:00
<p>If <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
<tt class="docutils literal"><span class="pre">random_access_iterator_tag</span></tt> or <tt class="docutils literal"><span class="pre">random_access_traversal_tag</span></tt>,
2004-01-13 13:36:55 +00:00
the following must must also be valid:</p>
2003-08-05 19:48:41 +00:00
<pre class="literal-block">
counting_iterator::difference_type n;
2004-01-13 13:36:55 +00:00
i += n;
n = i - j;
i &lt; j;
2003-08-05 19:48:41 +00:00
</pre>
</div>
<div class="section" id="counting-iterator-models">
2005-05-20 15:32:55 +00:00
<h1><a class="toc-backref" href="#id4" name="counting-iterator-models"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models</a></h1>
<p>Specializations of <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> model Readable Lvalue
2004-01-13 13:36:55 +00:00
Iterator. In addition, they model the concepts corresponding to the
2005-05-20 15:32:55 +00:00
iterator tags to which their <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible.
Also, if <tt class="docutils literal"><span class="pre">CategoryOrTraversal</span></tt> is not <tt class="docutils literal"><span class="pre">use_default</span></tt> then
<tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models the concept corresponding to the iterator
tag <tt class="docutils literal"><span class="pre">CategoryOrTraversal</span></tt>. Otherwise, if
<tt class="docutils literal"><span class="pre">numeric_limits&lt;Incrementable&gt;::is_specialized</span></tt>, then
<tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models Random Access Traversal Iterator.
Otherwise, <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models the same iterator traversal
concepts modeled by <tt class="docutils literal"><span class="pre">Incrementable</span></tt>.</p>
<p><tt class="docutils literal"><span class="pre">counting_iterator&lt;X,C1,D1&gt;</span></tt> is interoperable with
<tt class="docutils literal"><span class="pre">counting_iterator&lt;Y,C2,D2&gt;</span></tt> if and only if <tt class="docutils literal"><span class="pre">X</span></tt> is
interoperable with <tt class="docutils literal"><span class="pre">Y</span></tt>.</p>
</div>
2003-08-05 19:48:41 +00:00
<div class="section" id="counting-iterator-operations">
2005-05-20 15:32:55 +00:00
<h1><a class="toc-backref" href="#id5" name="counting-iterator-operations"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> operations</a></h1>
<p>In addition to the operations required by the concepts modeled by
2005-05-20 15:32:55 +00:00
<tt class="docutils literal"><span class="pre">counting_iterator</span></tt>, <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> provides the following
operations.</p>
2005-05-20 15:32:55 +00:00
<p><tt class="docutils literal"><span class="pre">counting_iterator();</span></tt></p>
<table class="docutils field-list" frame="void" rules="none">
2003-08-05 19:48:41 +00:00
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">Incrementable</span></tt> is Default Constructible.</td>
2004-01-13 14:10:54 +00:00
</tr>
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Effects:</th><td class="field-body">Default construct the member <tt class="docutils literal"><span class="pre">m_inc</span></tt>.</td>
2003-08-05 19:48:41 +00:00
</tr>
</tbody>
</table>
2005-05-20 15:32:55 +00:00
<p><tt class="docutils literal"><span class="pre">counting_iterator(counting_iterator</span> <span class="pre">const&amp;</span> <span class="pre">rhs);</span></tt></p>
<table class="docutils field-list" frame="void" rules="none">
2003-08-05 19:48:41 +00:00
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Effects:</th><td class="field-body">Construct member <tt class="docutils literal"><span class="pre">m_inc</span></tt> from <tt class="docutils literal"><span class="pre">rhs.m_inc</span></tt>.</td>
2003-08-05 19:48:41 +00:00
</tr>
</tbody>
</table>
2005-05-20 15:32:55 +00:00
<p><tt class="docutils literal"><span class="pre">explicit</span> <span class="pre">counting_iterator(Incrementable</span> <span class="pre">x);</span></tt></p>
<table class="docutils field-list" frame="void" rules="none">
2003-08-05 19:48:41 +00:00
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Effects:</th><td class="field-body">Construct member <tt class="docutils literal"><span class="pre">m_inc</span></tt> from <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
2004-01-12 00:48:21 +00:00
</tr>
</tbody>
</table>
2005-05-20 15:32:55 +00:00
<p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
<table class="docutils field-list" frame="void" rules="none">
2004-01-12 00:48:21 +00:00
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_inc</span></tt></td>
2004-01-12 00:48:21 +00:00
</tr>
</tbody>
</table>
2005-05-20 15:32:55 +00:00
<p><tt class="docutils literal"><span class="pre">counting_iterator&amp;</span> <span class="pre">operator++();</span></tt></p>
<table class="docutils field-list" frame="void" rules="none">
2004-01-12 00:48:21 +00:00
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">++m_inc</span></tt></td>
</tr>
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
</tr>
</tbody>
</table>
2005-05-20 15:32:55 +00:00
<p><tt class="docutils literal"><span class="pre">counting_iterator&amp;</span> <span class="pre">operator--();</span></tt></p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Effects:</th><td class="field-body"><tt class="docutils literal"><span class="pre">--m_inc</span></tt></td>
</tr>
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
2004-01-12 00:48:21 +00:00
</tr>
</tbody>
</table>
2005-05-20 15:32:55 +00:00
<p><tt class="docutils literal"><span class="pre">Incrementable</span> <span class="pre">const&amp;</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
<table class="docutils field-list" frame="void" rules="none">
2004-01-12 00:48:21 +00:00
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">m_inc</span></tt></td>
2004-01-12 00:48:21 +00:00
</tr>
</tbody>
</table>
<pre class="literal-block">
template &lt;class Incrementable&gt;
counting_iterator&lt;Incrementable&gt; make_counting_iterator(Incrementable x);
2004-01-12 00:48:21 +00:00
</pre>
2005-05-20 15:32:55 +00:00
<table class="docutils field-list" frame="void" rules="none">
2004-01-12 00:48:21 +00:00
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
2005-05-20 15:32:55 +00:00
<tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="docutils literal"><span class="pre">counting_iterator&lt;Incrementable&gt;</span></tt>
with <tt class="docutils literal"><span class="pre">current</span></tt> constructed from <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
2003-08-05 19:48:41 +00:00
</tr>
</tbody>
</table>
</div>
2004-01-12 00:48:21 +00:00
<div class="section" id="example">
2004-01-12 16:10:29 +00:00
<h1><a class="toc-backref" href="#id6" name="example">Example</a></h1>
2004-01-12 00:48:21 +00:00
<p>This example fills an array with numbers and a second array with
2005-05-20 15:32:55 +00:00
pointers into the first array, using <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> for both
tasks. Finally <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> is used to print out the numbers
2004-01-12 00:48:21 +00:00
into the first array via indirection through the second array.</p>
<pre class="literal-block">
int N = 7;
std::vector&lt;int&gt; numbers;
typedef std::vector&lt;int&gt;::iterator n_iter;
std::copy(boost::counting_iterator&lt;int&gt;(0),
boost::counting_iterator&lt;int&gt;(N),
std::back_inserter(numbers));
std::vector&lt;std::vector&lt;int&gt;::iterator&gt; pointers;
std::copy(boost::make_counting_iterator(numbers.begin()),
boost::make_counting_iterator(numbers.end()),
std::back_inserter(pointers));
std::cout &lt;&lt; &quot;indirectly printing out the numbers from 0 to &quot;
&lt;&lt; N &lt;&lt; std::endl;
std::copy(boost::make_indirect_iterator(pointers.begin()),
boost::make_indirect_iterator(pointers.end()),
std::ostream_iterator&lt;int&gt;(std::cout, &quot; &quot;));
std::cout &lt;&lt; std::endl;
</pre>
<p>The output is:</p>
<pre class="literal-block">
indirectly printing out the numbers from 0 to 7
0 1 2 3 4 5 6
</pre>
2004-01-12 16:10:29 +00:00
<p>The source code for this example can be found <a class="reference" href="../example/counting_iterator_example.cpp">here</a>.</p>
2003-08-05 19:48:41 +00:00
</div>
</div>
2005-05-20 15:32:55 +00:00
<hr class="docutils footer" />
2004-01-27 04:13:36 +00:00
<div class="footer">
<a class="reference" href="counting_iterator.rst">View document source</a>.
Generated by <a class="reference" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
</div>
2003-08-05 19:48:41 +00:00
</body>
</html>