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- <title>Filter 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="filter-iterator">
- <h1 class="title">Filter 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"><!-- 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) -->
- The filter iterator adaptor creates a view of an iterator range in
- which some elements of the range are skipped. A predicate function
- object controls which elements are skipped. When the predicate is
- applied to an element, if it returns <tt class="docutils literal"><span class="pre">true</span></tt> then the element is
- retained and if it returns <tt class="docutils literal"><span class="pre">false</span></tt> then the element is skipped
- over. When skipping over elements, it is necessary for the filter
- adaptor to know when to stop so as to avoid going past the end of the
- underlying range. A filter iterator is therefore constructed with pair
- of iterators indicating the range of elements in the unfiltered
- sequence to be traversed.</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="#filter-iterator-synopsis" id="id2"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> synopsis</a></li>
- <li><a class="reference internal" href="#filter-iterator-requirements" id="id3"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> requirements</a></li>
- <li><a class="reference internal" href="#filter-iterator-models" id="id4"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</a></li>
- <li><a class="reference internal" href="#filter-iterator-operations" id="id5"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> operations</a></li>
- <li><a class="reference internal" href="#example" id="id6">Example</a></li>
- </ul>
- </div>
- <div class="section" id="filter-iterator-synopsis">
- <h1><a class="toc-backref" href="#id2"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> synopsis</a></h1>
- <!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt -->
- <!-- 2004. Use, modification and distribution is subject to 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 Predicate, class Iterator>
- class filter_iterator
- {
- public:
- typedef iterator_traits<Iterator>::value_type value_type;
- typedef iterator_traits<Iterator>::reference reference;
- typedef iterator_traits<Iterator>::pointer pointer;
- typedef iterator_traits<Iterator>::difference_type difference_type;
- typedef /* see below */ iterator_category;
- filter_iterator();
- filter_iterator(Predicate f, Iterator x, Iterator end = Iterator());
- filter_iterator(Iterator x, Iterator end = Iterator());
- template<class OtherIterator>
- filter_iterator(
- filter_iterator<Predicate, OtherIterator> const& t
- , typename enable_if_convertible<OtherIterator, Iterator>::type* = 0 // exposition
- );
- Predicate predicate() const;
- Iterator end() const;
- Iterator const& base() const;
- reference operator*() const;
- filter_iterator& operator++();
- private:
- Predicate m_pred; // exposition only
- Iterator m_iter; // exposition only
- Iterator m_end; // exposition only
- };
- </pre>
- <p>If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Readable Lvalue Iterator and Bidirectional Traversal
- Iterator then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
- <tt class="docutils literal"><span class="pre">std::bidirectional_iterator_tag</span></tt>.
- Otherwise, if <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Readable Lvalue Iterator and Forward Traversal
- Iterator then <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
- <tt class="docutils literal"><span class="pre">std::forward_iterator_tag</span></tt>.
- Otherwise <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is
- convertible to <tt class="docutils literal"><span class="pre">std::input_iterator_tag</span></tt>.</p>
- </div>
- <div class="section" id="filter-iterator-requirements">
- <h1><a class="toc-backref" href="#id3"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> requirements</a></h1>
- <p>The <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument shall meet the requirements of Readable
- Iterator and Single Pass Iterator or it shall meet the requirements of
- Input Iterator.</p>
- <p>The <tt class="docutils literal"><span class="pre">Predicate</span></tt> argument must be Assignable, Copy Constructible, and
- the expression <tt class="docutils literal"><span class="pre">p(x)</span></tt> must be valid where <tt class="docutils literal"><span class="pre">p</span></tt> is an object of type
- <tt class="docutils literal"><span class="pre">Predicate</span></tt>, <tt class="docutils literal"><span class="pre">x</span></tt> is an object of type
- <tt class="docutils literal"><span class="pre">iterator_traits<Iterator>::value_type</span></tt>, and where the type of
- <tt class="docutils literal"><span class="pre">p(x)</span></tt> must be convertible to <tt class="docutils literal"><span class="pre">bool</span></tt>.</p>
- </div>
- <div class="section" id="filter-iterator-models">
- <h1><a class="toc-backref" href="#id4"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</a></h1>
- <p>The concepts that <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models are dependent on which
- concepts the <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument models, as specified in the
- following tables.</p>
- <table border="1" class="docutils">
- <colgroup>
- <col width="44%" />
- <col width="56%" />
- </colgroup>
- <thead valign="bottom">
- <tr><th class="head">If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models</th>
- <th class="head">then <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</th>
- </tr>
- </thead>
- <tbody valign="top">
- <tr><td>Single Pass Iterator</td>
- <td>Single Pass Iterator</td>
- </tr>
- <tr><td>Forward Traversal Iterator</td>
- <td>Forward Traversal Iterator</td>
- </tr>
- <tr><td>Bidirectional Traversal Iterator</td>
- <td>Bidirectional Traversal Iterator</td>
- </tr>
- </tbody>
- </table>
- <table border="1" class="docutils">
- <colgroup>
- <col width="41%" />
- <col width="59%" />
- </colgroup>
- <thead valign="bottom">
- <tr><th class="head">If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models</th>
- <th class="head">then <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</th>
- </tr>
- </thead>
- <tbody valign="top">
- <tr><td>Readable Iterator</td>
- <td>Readable Iterator</td>
- </tr>
- <tr><td>Writable Iterator</td>
- <td>Writable Iterator</td>
- </tr>
- <tr><td>Lvalue Iterator</td>
- <td>Lvalue Iterator</td>
- </tr>
- </tbody>
- </table>
- <table border="1" class="docutils">
- <colgroup>
- <col width="63%" />
- <col width="38%" />
- </colgroup>
- <thead valign="bottom">
- <tr><th class="head">If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models</th>
- <th class="head">then <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models</th>
- </tr>
- </thead>
- <tbody valign="top">
- <tr><td>Readable Iterator, Single Pass Iterator</td>
- <td>Input Iterator</td>
- </tr>
- <tr><td>Readable Lvalue Iterator, Forward Traversal Iterator</td>
- <td>Forward Iterator</td>
- </tr>
- <tr><td>Writable Lvalue Iterator, Forward Traversal Iterator</td>
- <td>Mutable Forward Iterator</td>
- </tr>
- <tr><td>Writable Lvalue Iterator, Bidirectional Iterator</td>
- <td>Mutable Bidirectional Iterator</td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">filter_iterator<P1,</span> <span class="pre">X></span></tt> is interoperable with <tt class="docutils literal"><span class="pre">filter_iterator<P2,</span> <span class="pre">Y></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="filter-iterator-operations">
- <h1><a class="toc-backref" href="#id5"><tt class="docutils literal"><span class="pre">filter_iterator</span></tt> operations</a></h1>
- <p>In addition to those operations required by the concepts that
- <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> models, <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> provides the following
- operations.</p>
- <p><tt class="docutils literal"><span class="pre">filter_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">Predicate</span></tt> and <tt class="docutils literal"><span class="pre">Iterator</span></tt> must be Default Constructible.</td>
- </tr>
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs a <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> whose``m_pred``, <tt class="docutils literal"><span class="pre">m_iter</span></tt>, and <tt class="docutils literal"><span class="pre">m_end</span></tt>
- members are a default constructed.</td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">filter_iterator(Predicate</span> <span class="pre">f,</span> <span class="pre">Iterator</span> <span class="pre">x,</span> <span class="pre">Iterator</span> <span class="pre">end</span> <span class="pre">=</span> <span class="pre">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">Effects:</th><td class="field-body">Constructs a <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> where <tt class="docutils literal"><span class="pre">m_iter</span></tt> is either
- the first position in the range <tt class="docutils literal"><span class="pre">[x,end)</span></tt> such that <tt class="docutils literal"><span class="pre">f(*m_iter)</span> <span class="pre">==</span> <span class="pre">true</span></tt>
- or else``m_iter == end``. The member <tt class="docutils literal"><span class="pre">m_pred</span></tt> is constructed from
- <tt class="docutils literal"><span class="pre">f</span></tt> and <tt class="docutils literal"><span class="pre">m_end</span></tt> from <tt class="docutils literal"><span class="pre">end</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">filter_iterator(Iterator</span> <span class="pre">x,</span> <span class="pre">Iterator</span> <span class="pre">end</span> <span class="pre">=</span> <span class="pre">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">Predicate</span></tt> must be Default Constructible and
- <tt class="docutils literal"><span class="pre">Predicate</span></tt> is a class type (not a function pointer).</td>
- </tr>
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs a <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> where <tt class="docutils literal"><span class="pre">m_iter</span></tt> is either
- the first position in the range <tt class="docutils literal"><span class="pre">[x,end)</span></tt> such that <tt class="docutils literal"><span class="pre">m_pred(*m_iter)</span> <span class="pre">==</span> <span class="pre">true</span></tt>
- or else``m_iter == end``. The member <tt class="docutils literal"><span class="pre">m_pred</span></tt> is default constructed.</td>
- </tr>
- </tbody>
- </table>
- <pre class="literal-block">
- template <class OtherIterator>
- filter_iterator(
- filter_iterator<Predicate, OtherIterator> const& t
- , typename enable_if_convertible<OtherIterator, Iterator>::type* = 0 // exposition
- );``
- </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">Requires:</th><td class="field-body"><tt class="docutils literal"><span class="pre">OtherIterator</span></tt> is implicitly convertible to <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</td>
- </tr>
- <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs a filter iterator whose members are copied from <tt class="docutils literal"><span class="pre">t</span></tt>.</td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">Predicate</span> <span class="pre">predicate()</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_pred</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">Iterator</span> <span class="pre">end()</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_end</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">Iterator</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_iterator</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_iter</span></tt></td>
- </tr>
- </tbody>
- </table>
- <p><tt class="docutils literal"><span class="pre">filter_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">Increments <tt class="docutils literal"><span class="pre">m_iter</span></tt> and then continues to
- increment <tt class="docutils literal"><span class="pre">m_iter</span></tt> until either <tt class="docutils literal"><span class="pre">m_iter</span> <span class="pre">==</span> <span class="pre">m_end</span></tt>
- or <tt class="docutils literal"><span class="pre">m_pred(*m_iter)</span> <span class="pre">==</span> <span class="pre">true</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>
- <!-- 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 Predicate, class Iterator>
- filter_iterator<Predicate,Iterator>
- make_filter_iterator(Predicate f, Iterator x, Iterator end = Iterator());
- </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">filter_iterator<Predicate,Iterator>(f, x, end)</td>
- </tr>
- </tbody>
- </table>
- <pre class="literal-block">
- template <class Predicate, class Iterator>
- filter_iterator<Predicate,Iterator>
- make_filter_iterator(Iterator x, Iterator end = Iterator());
- </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">filter_iterator<Predicate,Iterator>(x, end)</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 uses <tt class="docutils literal"><span class="pre">filter_iterator</span></tt> and then
- <tt class="docutils literal"><span class="pre">make_filter_iterator</span></tt> to output only the positive integers from an
- array of integers. Then <tt class="docutils literal"><span class="pre">make_filter_iterator</span></tt> is is used to output
- the integers greater than <tt class="docutils literal"><span class="pre">-2</span></tt>.</p>
- <pre class="literal-block">
- struct is_positive_number {
- bool operator()(int x) { return 0 < x; }
- };
- int main()
- {
- int numbers_[] = { 0, -1, 4, -3, 5, 8, -2 };
- const int N = sizeof(numbers_)/sizeof(int);
- typedef int* base_iterator;
- base_iterator numbers(numbers_);
- // Example using filter_iterator
- typedef boost::filter_iterator<is_positive_number, base_iterator>
- FilterIter;
- is_positive_number predicate;
- FilterIter filter_iter_first(predicate, numbers, numbers + N);
- FilterIter filter_iter_last(predicate, numbers + N, numbers + N);
- std::copy(filter_iter_first, filter_iter_last, std::ostream_iterator<int>(std::cout, " "));
- std::cout << std::endl;
- // Example using make_filter_iterator()
- std::copy(boost::make_filter_iterator<is_positive_number>(numbers, numbers + N),
- boost::make_filter_iterator<is_positive_number>(numbers + N, numbers + N),
- std::ostream_iterator<int>(std::cout, " "));
- std::cout << std::endl;
- // Another example using make_filter_iterator()
- std::copy(
- boost::make_filter_iterator(
- std::bind2nd(std::greater<int>(), -2)
- , numbers, numbers + N)
- , boost::make_filter_iterator(
- std::bind2nd(std::greater<int>(), -2)
- , numbers + N, numbers + N)
- , std::ostream_iterator<int>(std::cout, " ")
- );
- std::cout << std::endl;
- return boost::exit_success;
- }
- </pre>
- <p>The output is:</p>
- <pre class="literal-block">
- 4 5 8
- 4 5 8
- 0 -1 4 5 8
- </pre>
- <p>The source code for this example can be found <a class="reference external" href="../example/filter_iterator_example.cpp">here</a>.</p>
- </div>
- </div>
- <div class="footer">
- <hr class="footer" />
- <a class="reference external" href="filter_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.
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