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[SVN r9094]
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Jeremy Siek
2001-02-10 22:33:43 +00:00
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<meta name="GENERATOR" content="Microsoft FrontPage 4.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<title>Filter Iterator Adaptor Documentation</title>
</head>
<body bgcolor="#FFFFFF" text="#000000">
<img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)"
align="center" width="277" height="86">
<h1>Filter Iterator Adaptor</h1>
Defined in header
<a href="../../boost/iterator_adaptors.hpp">boost/iterator_adaptors.hpp</a>
<p>
The filter iterator adaptor ...
<h3>Example</h3>
The following example uses filter iterator to print out all the
positive integers in an array.
<pre>
#include &lt;boost/config.hpp&gt;
#include &lt;algorithm&gt;
#include &lt;iostream&gt;
#include &lt;boost/iterator_adaptors.hpp&gt;
struct is_positive_number {
bool operator()(int x) { return 0 &lt; x; }
};
int main()
{
int numbers[] = { 0, -1, 4, -3, 5, 8, -2 };
const int N = sizeof(numbers)/sizeof(int);
std::copy(boost::make_filter_iterator&lt;is_positive_number&gt;(numbers, numbers + N),
boost::make_filter_iterator&lt;is_positive_number&gt;(numbers + N, numbers + N),
std::ostream_iterator&lt;int&gt;(std::cout, " "));
std::cout &lt;&lt; std::endl;
return 0;
}
</pre>
The output is:
<pre>
4 5 8
</pre>
The filter iterator adaptors
models <a href="www.sgi.com/tech/stl/ForwardIterator.html">ForwardIterator</a>
<h3>The Filter Iterator Type Generator</h3>
<pre>
template &lt;class Predicate,
class Iterator,
class Value = <i>value default</i>,
class Pointer = <i>pointer default</i>,
class Reference = <i>reference default</i>,
class Category = <i>category default</i>,
class Distance = <i>difference type default</i>&gt;
class filter_iterator_generator
{
typedef ... type;
typedef ... policies_type;
}
</pre>
<p>
show another example and explain defaults...
<h3>The Make Filter Iterator Helper Function</h3>
<pre>
template &lt;class Predicate, class Iterator&gt;
inline typename detail::filter_generator&lt;Predicate, Iterator&gt;::type
make_filter_iterator(Iterator first, Iterator last, const Predicate& p = Predicate())
</pre>
<hr>
<p>Revised <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %b %Y" startspan -->10 Feb 2001<!--webbot bot="Timestamp" endspan i-checksum="14373" --></p>
<p><EFBFBD> Copyright Jeremy Siek 2000. Permission to copy, use,
modify, sell and distribute this document is granted provided this copyright
notice appears in all copies. This document is provided &quot;as is&quot;
without express or implied warranty, and with no claim as to its suitability for
any purpose.</p>
</body>
</html>

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// Example of using the filter iterator adaptor from
// boost/iterator_adaptors.hpp.
// (C) Copyright Jeremy Siek 1999. Permission to copy, use, modify,
// sell and distribute this software is granted provided this
// copyright notice appears in all copies. This software is provided
// "as is" without express or implied warranty, and with no claim as
// to its suitability for any purpose.
#include <boost/config.hpp>
#include <algorithm>
#include <iostream>
#include <boost/iterator_adaptors.hpp>
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);
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;
return 0;
}