<?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>Reverse 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="reverse-iterator"> <h1 class="title">Reverse 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 reverse iterator adaptor iterates through the adapted iterator range in the opposite direction.</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="#reverse-iterator-synopsis" id="id2"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> synopsis</a></li> <li><a class="reference internal" href="#reverse-iterator-requirements" id="id3"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> requirements</a></li> <li><a class="reference internal" href="#reverse-iterator-models" id="id4"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> models</a></li> <li><a class="reference internal" href="#reverse-iterator-operations" id="id5"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> operations</a></li> <li><a class="reference internal" href="#example" id="id6">Example</a></li> </ul> </div> <div class="section" id="reverse-iterator-synopsis"> <h1><a class="toc-backref" href="#id2"><tt class="docutils literal"><span class="pre">reverse_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 Iterator> class reverse_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; reverse_iterator() {} explicit reverse_iterator(Iterator x) ; template<class OtherIterator> reverse_iterator( reverse_iterator<OtherIterator> const& r , typename enable_if_convertible<OtherIterator, Iterator>::type* = 0 // exposition ); Iterator const& base() const; reference operator*() const; reverse_iterator& operator++(); reverse_iterator& operator--(); private: Iterator m_iterator; // exposition }; </pre> <p>If <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Random Access Traversal Iterator and Readable Lvalue Iterator, then <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>. Otherwise, if <tt class="docutils literal"><span class="pre">Iterator</span></tt> models Bidirectional Traversal Iterator and Readable Lvalue Iterator, then <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>. Otherwise, <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to <tt class="docutils literal"><span class="pre">input_iterator_tag</span></tt>.</p> </div> <div class="section" id="reverse-iterator-requirements"> <h1><a class="toc-backref" href="#id3"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> requirements</a></h1> <p><tt class="docutils literal"><span class="pre">Iterator</span></tt> must be a model of Bidirectional Traversal Iterator. The type <tt class="docutils literal"><span class="pre">iterator_traits<Iterator>::reference</span></tt> must be the type of <tt class="docutils literal"><span class="pre">*i</span></tt>, where <tt class="docutils literal"><span class="pre">i</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Iterator</span></tt>.</p> </div> <div class="section" id="reverse-iterator-models"> <h1><a class="toc-backref" href="#id4"><tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> models</a></h1> <p>A specialization of <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> models the same iterator traversal and iterator access concepts modeled by its <tt class="docutils literal"><span class="pre">Iterator</span></tt> argument. In addition, it may model old iterator concepts specified in the following table:</p> <table border="1" class="docutils"> <colgroup> <col width="53%" /> <col width="47%" /> </colgroup> <thead valign="bottom"> <tr><th class="head">If <tt class="docutils literal"><span class="pre">I</span></tt> models</th> <th class="head">then <tt class="docutils literal"><span class="pre">reverse_iterator<I></span></tt> models</th> </tr> </thead> <tbody valign="top"> <tr><td>Readable Lvalue Iterator, Bidirectional Traversal Iterator</td> <td>Bidirectional Iterator</td> </tr> <tr><td>Writable Lvalue Iterator, Bidirectional Traversal Iterator</td> <td>Mutable Bidirectional Iterator</td> </tr> <tr><td>Readable Lvalue Iterator, Random Access Traversal Iterator</td> <td>Random Access Iterator</td> </tr> <tr><td>Writable Lvalue Iterator, Random Access Traversal Iterator</td> <td>Mutable Random Access Iterator</td> </tr> </tbody> </table> <p><tt class="docutils literal"><span class="pre">reverse_iterator<X></span></tt> is interoperable with <tt class="docutils literal"><span class="pre">reverse_iterator<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="reverse-iterator-operations"> <h1><a class="toc-backref" href="#id5"><tt class="docutils literal"><span class="pre">reverse_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">reverse_iterator</span></tt>, <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> provides the following operations.</p> <p><tt class="docutils literal"><span class="pre">reverse_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">Iterator</span></tt> must be Default Constructible.</td> </tr> <tr class="field"><th class="field-name">Effects:</th><td class="field-body">Constructs an instance of <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_iterator</span></tt> default constructed.</td> </tr> </tbody> </table> <p><tt class="docutils literal"><span class="pre">explicit</span> <span class="pre">reverse_iterator(Iterator</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">Constructs an instance of <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> with <tt class="docutils literal"><span class="pre">m_iterator</span></tt> copy constructed from <tt class="docutils literal"><span class="pre">x</span></tt>.</td> </tr> </tbody> </table> <pre class="literal-block"> template<class OtherIterator> reverse_iterator( reverse_iterator<OtherIterator> const& r , 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 instance of <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt> whose <tt class="docutils literal"><span class="pre">m_iterator</span></tt> subobject is constructed from <tt class="docutils literal"><span class="pre">y.base()</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">Effects:</th><td class="field-body"></td> </tr> </tbody> </table> <pre class="literal-block"> Iterator tmp = m_iterator; return *--tmp; </pre> <p><tt class="docutils literal"><span class="pre">reverse_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_iterator</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">reverse_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_iterator</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 BidirectionalIterator> reverse_iterator<BidirectionalIterator>n make_reverse_iterator(BidirectionalIterator 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">reverse_iterator<BidirectionalIterator></span></tt> with a <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>The following example prints an array of characters in reverse order using <tt class="docutils literal"><span class="pre">reverse_iterator</span></tt>.</p> <pre class="literal-block"> char letters_[] = "hello world!"; const int N = sizeof(letters_)/sizeof(char) - 1; typedef char* base_iterator; base_iterator letters(letters_); std::cout << "original sequence of letters:\t\t\t" << letters_ << std::endl; boost::reverse_iterator<base_iterator> reverse_letters_first(letters + N), reverse_letters_last(letters); std::cout << "sequence in reverse order:\t\t\t"; std::copy(reverse_letters_first, reverse_letters_last, std::ostream_iterator<char>(std::cout)); std::cout << std::endl; std::cout << "sequence in double-reversed (normal) order:\t"; std::copy(boost::make_reverse_iterator(reverse_letters_last), boost::make_reverse_iterator(reverse_letters_first), std::ostream_iterator<char>(std::cout)); std::cout << std::endl; </pre> <p>The output is:</p> <pre class="literal-block"> original sequence of letters: hello world! sequence in reverse order: !dlrow olleh sequence in double-reversed (normal) order: hello world! </pre> <p>The source code for this example can be found <a class="reference external" href="../example/reverse_iterator_example.cpp">here</a>.</p> </div> </div> <div class="footer"> <hr class="footer" /> <a class="reference external" href="reverse_iterator.rst">View document source</a>. 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