123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301 |
- <?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" />
- <meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
- <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="2006-09-11" />
- <meta name="copyright" content="Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003." />
- <link rel="stylesheet" href="../../../rst.css" type="text/css" />
- </head>
- <body>
- <div class="document" id="counting-iterator">
- <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 external" href="mailto:dave@boost-consulting.com">dave@boost-consulting.com</a>, <a class="reference external" href="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</a>, <a class="last reference external" href="mailto:witt@ive.uni-hannover.de">witt@ive.uni-hannover.de</a></td></tr>
- <tr><th class="docinfo-name">Organization:</th>
- <td><a class="first reference external" href="http://www.boost-consulting.com">Boost Consulting</a>, Indiana University <a class="reference external" href="http://www.osl.iu.edu">Open Systems
- Lab</a>, University of Hanover <a class="last reference external" 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>2006-09-11</td></tr>
- <tr><th class="docinfo-name">Copyright:</th>
- <td>Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003.</td></tr>
- </tbody>
- </table>
- <!-- Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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="docutils literal"><span class="pre">std::copy()</span></tt>? The only iterator
- operation missing from builtin integer types is an
- <tt class="docutils 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 incrementable type.</p>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <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
- returns the current value of the object. All other iterator operations
- are forwarded to the adapted object.</p>
- </td>
- </tr>
- </tbody>
- </table>
- <div class="contents topic" id="table-of-contents">
- <p class="topic-title first">Table of Contents</p>
- <ul class="simple">
- <li><a class="reference internal" href="#counting-iterator-synopsis" id="id2"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> synopsis</a></li>
- <li><a class="reference internal" href="#counting-iterator-requirements" id="id3"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> requirements</a></li>
- <li><a class="reference internal" href="#counting-iterator-models" id="id4"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models</a></li>
- <li><a class="reference internal" href="#counting-iterator-operations" id="id5"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> operations</a></li>
- <li><a class="reference internal" href="#example" id="id6">Example</a></li>
- </ul>
- </div>
- <div class="section" id="counting-iterator-synopsis">
- <h1><a class="toc-backref" href="#id2"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> synopsis</a></h1>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <pre class="literal-block">
- template <
- class Incrementable
- , class CategoryOrTraversal = use_default
- , class Difference = use_default
- >
- class counting_iterator
- {
- public:
- typedef Incrementable value_type;
- typedef const Incrementable& reference;
- typedef const Incrementable* pointer;
- typedef /* see below */ difference_type;
- typedef /* see below */ iterator_category;
- counting_iterator();
- counting_iterator(counting_iterator const& rhs);
- explicit counting_iterator(Incrementable x);
- Incrementable const& base() const;
- reference operator*() const;
- counting_iterator& operator++();
- counting_iterator& operator--();
- private:
- Incrementable m_inc; // exposition
- };
- </pre>
- <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<Incrementable>::is_specialized)
- return <a class="reference external" href="iterator_facade.html#iterator-category"><em>iterator-category</em></a>(
- random_access_traversal_tag, Incrementable, const Incrementable&)
- else
- return <a class="reference external" href="iterator_facade.html#iterator-category"><em>iterator-category</em></a>(
- iterator_traversal<Incrementable>::type,
- Incrementable, const Incrementable&)
- </pre>
- <dl class="docutils">
- <dt>[<em>Note:</em> implementers are encouraged to provide an implementation of</dt>
- <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<Incrementable>::is_specialized</span></tt>
- is true.]</dd>
- </dl>
- </div>
- <div class="section" id="counting-iterator-requirements">
- <h1><a class="toc-backref" href="#id3"><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>
- <pre class="literal-block">
- Incrementable i, j;
- ++i; // pre-increment
- i == j; // operator equal
- </pre>
- <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>,
- the following expression must also be well-formed:</p>
- <pre class="literal-block">
- --i
- </pre>
- <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>,
- the following must must also be valid:</p>
- <pre class="literal-block">
- counting_iterator::difference_type n;
- i += n;
- n = i - j;
- i < j;
- </pre>
- </div>
- <div class="section" id="counting-iterator-models">
- <h1><a class="toc-backref" href="#id4"><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
- Iterator. In addition, they model the concepts corresponding to the
- 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<Incrementable>::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<X,C1,D1></span></tt> is interoperable with
- <tt class="docutils literal"><span class="pre">counting_iterator<Y,C2,D2></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>
- <div class="section" id="counting-iterator-operations">
- <h1><a class="toc-backref" href="#id5"><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
- <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>
- <p><tt class="docutils literal"><span class="pre">counting_iterator();</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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>
- </tr>
- <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>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">counting_iterator(counting_iterator</span> <span class="pre">const&</span> <span class="pre">rhs);</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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>
- </tr>
- </tbody>
- </table>
- <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">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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>
- </tr>
- </tbody>
- </table>
- <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">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">counting_iterator&</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">
- <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>
- <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>
- <p><tt class="docutils literal"><span class="pre">counting_iterator&</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">
- <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>
- <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>
- <p><tt class="docutils literal"><span class="pre">Incrementable</span> <span class="pre">const&</span> <span class="pre">base()</span> <span class="pre">const;</span></tt></p>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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>
- </tr>
- </tbody>
- </table>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- <pre class="literal-block">
- template <class Incrementable>
- counting_iterator<Incrementable> make_counting_iterator(Incrementable x);
- </pre>
- <table class="docutils field-list" frame="void" rules="none">
- <col class="field-name" />
- <col class="field-body" />
- <tbody valign="top">
- <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<Incrementable></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>
- </tr>
- </tbody>
- </table>
- <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
- <!-- Software License, Version 1.0. (See accompanying -->
- <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
- </div>
- <div class="section" id="example">
- <h1><a class="toc-backref" href="#id6">Example</a></h1>
- <p>This example fills an array with numbers and a second array with
- 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
- into the first array via indirection through the second array.</p>
- <pre class="literal-block">
- int N = 7;
- std::vector<int> numbers;
- typedef std::vector<int>::iterator n_iter;
- std::copy(boost::counting_iterator<int>(0),
- boost::counting_iterator<int>(N),
- std::back_inserter(numbers));
- std::vector<std::vector<int>::iterator> pointers;
- std::copy(boost::make_counting_iterator(numbers.begin()),
- boost::make_counting_iterator(numbers.end()),
- std::back_inserter(pointers));
- std::cout << "indirectly printing out the numbers from 0 to "
- << N << std::endl;
- std::copy(boost::make_indirect_iterator(pointers.begin()),
- boost::make_indirect_iterator(pointers.end()),
- std::ostream_iterator<int>(std::cout, " "));
- std::cout << 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>
- <p>The source code for this example can be found <a class="reference external" href="../example/counting_iterator_example.cpp">here</a>.</p>
- </div>
- </div>
- <div class="footer">
- <hr class="footer" />
- <a class="reference external" href="counting_iterator.rst">View document source</a>.
- Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
- </div>
- </body>
- </html>
|