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302 lines
18 KiB
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<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
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<title>Counting Iterator</title>
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<meta name="author" content="David Abrahams, Jeremy Siek, Thomas Witt" />
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<meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" />
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<meta name="date" content="2006-09-11" />
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<meta name="copyright" content="Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003." />
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<link rel="stylesheet" href="../../../rst.css" type="text/css" />
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</head>
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<body>
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<div class="document" id="counting-iterator">
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<h1 class="title">Counting Iterator</h1>
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<table class="docinfo" frame="void" rules="none">
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<col class="docinfo-name" />
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<col class="docinfo-content" />
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<tbody valign="top">
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<tr><th class="docinfo-name">Author:</th>
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<td>David Abrahams, Jeremy Siek, Thomas Witt</td></tr>
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<tr><th class="docinfo-name">Contact:</th>
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<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>
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<tr><th class="docinfo-name">Organization:</th>
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<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
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Lab</a>, University of Hanover <a class="last reference external" href="http://www.ive.uni-hannover.de">Institute for Transport
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Railway Operation and Construction</a></td></tr>
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<tr><th class="docinfo-name">Date:</th>
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<td>2006-09-11</td></tr>
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<tr><th class="docinfo-name">Copyright:</th>
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<td>Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003.</td></tr>
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</tbody>
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</table>
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<!-- Distributed under the Boost -->
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<!-- Software License, Version 1.0. (See accompanying -->
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<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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
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through one hundred using <tt class="docutils literal"><span class="pre">std::copy()</span></tt>? The only iterator
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operation missing from builtin integer types is an
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<tt class="docutils literal"><span class="pre">operator*()</span></tt> that returns the current value of the integer.
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The counting iterator adaptor adds this crucial piece of
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functionality to whatever type it wraps. One can use the
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counting iterator adaptor not only with integer types, but with
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any incrementable type.</p>
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
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<!-- Software License, Version 1.0. (See accompanying -->
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<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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<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
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returns the current value of the object. All other iterator operations
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are forwarded to the adapted object.</p>
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</td>
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</tr>
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</tbody>
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</table>
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<div class="contents topic" id="table-of-contents">
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<p class="topic-title first">Table of Contents</p>
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<ul class="simple">
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<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>
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<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>
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<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>
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<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>
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<li><a class="reference internal" href="#example" id="id6">Example</a></li>
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</ul>
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</div>
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<div class="section" id="counting-iterator-synopsis">
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<h1><a class="toc-backref" href="#id2"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> synopsis</a></h1>
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
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<!-- Software License, Version 1.0. (See accompanying -->
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<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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<pre class="literal-block">
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template <
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class Incrementable
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, class CategoryOrTraversal = use_default
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, class Difference = use_default
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>
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class counting_iterator
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{
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public:
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typedef Incrementable value_type;
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typedef const Incrementable& reference;
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typedef const Incrementable* pointer;
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typedef /* see below */ difference_type;
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typedef /* see below */ iterator_category;
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counting_iterator();
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counting_iterator(counting_iterator const& rhs);
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explicit counting_iterator(Incrementable x);
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Incrementable const& base() const;
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reference operator*() const;
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counting_iterator& operator++();
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counting_iterator& operator--();
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private:
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Incrementable m_inc; // exposition
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};
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</pre>
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<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
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<tt class="docutils literal"><span class="pre">difference_type</span></tt> is an unspecified signed integral
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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>
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<p><tt class="docutils literal"><span class="pre">iterator_category</span></tt> is determined according to the following
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algorithm:</p>
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<pre class="literal-block">
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if (CategoryOrTraversal is not use_default)
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return CategoryOrTraversal
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else if (numeric_limits<Incrementable>::is_specialized)
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return <a class="reference external" href="iterator_facade.html#iterator-category"><em>iterator-category</em></a>(
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random_access_traversal_tag, Incrementable, const Incrementable&)
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else
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return <a class="reference external" href="iterator_facade.html#iterator-category"><em>iterator-category</em></a>(
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iterator_traversal<Incrementable>::type,
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Incrementable, const Incrementable&)
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</pre>
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<dl class="docutils">
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<dt>[<em>Note:</em> implementers are encouraged to provide an implementation of</dt>
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<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
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the cases where <tt class="docutils literal"><span class="pre">std::numeric_limits<Incrementable>::is_specialized</span></tt>
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is true.]</dd>
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</dl>
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</div>
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<div class="section" id="counting-iterator-requirements">
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<h1><a class="toc-backref" href="#id3"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> requirements</a></h1>
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<p>The <tt class="docutils literal"><span class="pre">Incrementable</span></tt> argument shall be Copy Constructible and Assignable.</p>
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<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>
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or <tt class="docutils literal"><span class="pre">forward_traversal_tag</span></tt>, the following must be well-formed:</p>
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<pre class="literal-block">
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Incrementable i, j;
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++i; // pre-increment
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i == j; // operator equal
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</pre>
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<p>If <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
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<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>,
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the following expression must also be well-formed:</p>
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<pre class="literal-block">
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--i
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</pre>
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<p>If <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible to
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<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>,
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the following must must also be valid:</p>
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<pre class="literal-block">
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counting_iterator::difference_type n;
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i += n;
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n = i - j;
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i < j;
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</pre>
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</div>
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<div class="section" id="counting-iterator-models">
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<h1><a class="toc-backref" href="#id4"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models</a></h1>
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<p>Specializations of <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> model Readable Lvalue
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Iterator. In addition, they model the concepts corresponding to the
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iterator tags to which their <tt class="docutils literal"><span class="pre">iterator_category</span></tt> is convertible.
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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
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<tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models the concept corresponding to the iterator
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tag <tt class="docutils literal"><span class="pre">CategoryOrTraversal</span></tt>. Otherwise, if
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<tt class="docutils literal"><span class="pre">numeric_limits<Incrementable>::is_specialized</span></tt>, then
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<tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models Random Access Traversal Iterator.
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Otherwise, <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> models the same iterator traversal
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concepts modeled by <tt class="docutils literal"><span class="pre">Incrementable</span></tt>.</p>
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<p><tt class="docutils literal"><span class="pre">counting_iterator<X,C1,D1></span></tt> is interoperable with
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<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
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interoperable with <tt class="docutils literal"><span class="pre">Y</span></tt>.</p>
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</div>
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<div class="section" id="counting-iterator-operations">
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<h1><a class="toc-backref" href="#id5"><tt class="docutils literal"><span class="pre">counting_iterator</span></tt> operations</a></h1>
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<p>In addition to the operations required by the concepts modeled by
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<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
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operations.</p>
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<p><tt class="docutils literal"><span class="pre">counting_iterator();</span></tt></p>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</tr>
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<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>
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</tr>
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</tbody>
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</table>
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<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>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</tr>
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</tbody>
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</table>
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<p><tt class="docutils literal"><span class="pre">explicit</span> <span class="pre">counting_iterator(Incrementable</span> <span class="pre">x);</span></tt></p>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</tr>
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</tbody>
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</table>
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<p><tt class="docutils literal"><span class="pre">reference</span> <span class="pre">operator*()</span> <span class="pre">const;</span></tt></p>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</tr>
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</tbody>
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</table>
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<p><tt class="docutils literal"><span class="pre">counting_iterator&</span> <span class="pre">operator++();</span></tt></p>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</tr>
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
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</tr>
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</tbody>
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</table>
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<p><tt class="docutils literal"><span class="pre">counting_iterator&</span> <span class="pre">operator--();</span></tt></p>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</tr>
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<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><tt class="docutils literal"><span class="pre">*this</span></tt></td>
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</tr>
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</tbody>
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</table>
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<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>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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</tr>
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</tbody>
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</table>
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
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<!-- Software License, Version 1.0. (See accompanying -->
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||
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<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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<pre class="literal-block">
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template <class Incrementable>
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counting_iterator<Incrementable> make_counting_iterator(Incrementable x);
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</pre>
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<table class="docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<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>
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with <tt class="docutils literal"><span class="pre">current</span></tt> constructed from <tt class="docutils literal"><span class="pre">x</span></tt>.</td>
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</tr>
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</tbody>
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</table>
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
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<!-- Software License, Version 1.0. (See accompanying -->
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<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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</div>
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<div class="section" id="example">
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<h1><a class="toc-backref" href="#id6">Example</a></h1>
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<p>This example fills an array with numbers and a second array with
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pointers into the first array, using <tt class="docutils literal"><span class="pre">counting_iterator</span></tt> for both
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tasks. Finally <tt class="docutils literal"><span class="pre">indirect_iterator</span></tt> is used to print out the numbers
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into the first array via indirection through the second array.</p>
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<pre class="literal-block">
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int N = 7;
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std::vector<int> numbers;
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typedef std::vector<int>::iterator n_iter;
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std::copy(boost::counting_iterator<int>(0),
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boost::counting_iterator<int>(N),
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std::back_inserter(numbers));
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std::vector<std::vector<int>::iterator> pointers;
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std::copy(boost::make_counting_iterator(numbers.begin()),
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boost::make_counting_iterator(numbers.end()),
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std::back_inserter(pointers));
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std::cout << "indirectly printing out the numbers from 0 to "
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<< N << std::endl;
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std::copy(boost::make_indirect_iterator(pointers.begin()),
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boost::make_indirect_iterator(pointers.end()),
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std::ostream_iterator<int>(std::cout, " "));
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std::cout << std::endl;
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</pre>
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<p>The output is:</p>
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<pre class="literal-block">
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indirectly printing out the numbers from 0 to 7
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0 1 2 3 4 5 6
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</pre>
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<p>The source code for this example can be found <a class="reference external" href="../example/counting_iterator_example.cpp">here</a>.</p>
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</div>
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</div>
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<div class="footer">
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<hr class="footer" />
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<a class="reference external" href="counting_iterator.rst">View document source</a>.
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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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</div>
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</body>
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</html>
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