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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
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<meta name="GENERATOR" content="Microsoft FrontPage 4.0">
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<meta name="ProgId" content="FrontPage.Editor.Document">
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<title>Filter Iterator Adaptor Documentation</title>
|
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</head>
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<body bgcolor="#FFFFFF" text="#000000">
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<img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)"
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align="center" width="277" height="86">
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<h1>Filter Iterator Adaptor</h1>
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Defined in header
|
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<a href="../../boost/iterator_adaptors.hpp">boost/iterator_adaptors.hpp</a>
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<p>
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The filter iterator adaptor creates a view of an iterator range in
|
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which some elements of the range are skipped over. A <a
|
||||
href="http://www.sgi.com/tech/stl/Predicate.html">Predicate</a>
|
||||
function object controls which elements are skipped. When the
|
||||
predicate is applied to an element, if it returns <tt>true</tt> then
|
||||
the element is retained and if it returns <tt>false</tt> then the
|
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element is skipped over.
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<h2>Synopsis</h2>
|
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|
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<pre>
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namespace boost {
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template <class Predicate, class BaseIterator, ...>
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class filter_iterator_generator;
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template <class Predicate, class BaseIterator>
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typename filter_iterator_generator<Predicate, BaseIterator>::type
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||||
make_filter_iterator(BaseIterator first, BaseIterator last, const Predicate& p = Predicate());
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}
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||||
</pre>
|
||||
|
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<hr>
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<h2><a name="filter_iterator_generator">The Filter Iterator Type
|
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Generator</a></h2>
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|
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The class <tt>filter_iterator_generator</tt> is a helper class whose
|
||||
purpose is to construct a filter iterator type. The template
|
||||
parameters for this class are the <tt>Predicate</tt> function object
|
||||
type and the <tt>BaseIterator</tt> type that is being wrapped. In
|
||||
most cases the associated types for the wrapped iterator can be
|
||||
deduced from <tt>std::iterator_traits</tt>, but in some situations the
|
||||
user may want to override these types, so there are also template
|
||||
parameters for each of the iterator's associated types.
|
||||
|
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<pre>
|
||||
template <class Predicate, class BaseIterator,
|
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class Value, class Reference, class Pointer, class Category, class Distance>
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class filter_iterator_generator
|
||||
{
|
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public:
|
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typedef <tt><a href="./iterator_adaptors.htm#iterator_adaptor">iterator_adaptor</a><...></tt> type; // the resulting filter iterator type
|
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}
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</pre>
|
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|
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|
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<h3>Example</h3>
|
||||
|
||||
The following example uses filter iterator to print out all the
|
||||
positive integers in an array.
|
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|
||||
<pre>
|
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struct is_positive_number {
|
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bool operator()(int x) { return 0 < x; }
|
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};
|
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int main() {
|
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int numbers[] = { 0, -1, 4, -3, 5, 8, -2 };
|
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const int N = sizeof(numbers)/sizeof(int);
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|
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typedef boost::filter_iterator_generator<is_positive_number, int*, int>::type FilterIter;
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is_positive_number predicate;
|
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FilterIter::policies_type policies(predicate, numbers + N);
|
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FilterIter filter_iter_first(numbers, policies);
|
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FilterIter filter_iter_last(numbers + N, policies);
|
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|
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std::copy(filter_iter_first, filter_iter_last, std::ostream_iterator<int>(std::cout, " "));
|
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std::cout << std::endl;
|
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return 0;
|
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}
|
||||
</pre>
|
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The output is:
|
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<pre>
|
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4 5 8
|
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</pre>
|
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|
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|
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<h3>Template Parameters</h3>
|
||||
|
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<Table border>
|
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<TR>
|
||||
<TH>Parameter</TH><TH>Description</TH>
|
||||
</TR>
|
||||
|
||||
<TR>
|
||||
<TD><a href="http://www.sgi.com/tech/stl/Predicate.html"><tt>Predicate</tt></a></TD>
|
||||
<TD>The function object that determines which elements are retained and which elements are skipped.
|
||||
</TR>
|
||||
|
||||
<TR>
|
||||
<TD><tt>BaseIterator</tt></TD>
|
||||
<TD>The iterator type being wrapped. This type must at least be a model
|
||||
of the <a href="http://www.sgi.com/tech/stl/InputIterator">InputIterator</a> concept.</TD>
|
||||
</TR>
|
||||
|
||||
<TR>
|
||||
<TD><tt>Value</tt></TD>
|
||||
<TD>The <tt>value_type</tt> of the resulting iterator,
|
||||
unless const. If const, a conforming compiler strips constness for the
|
||||
<tt>value_type</tt>. Typically the default for this parameter is the
|
||||
appropriate type<a href="#1">[1]</a>.<br> <b>Default:</b>
|
||||
<tt>std::iterator_traits<BaseIterator>::value_type</TD>
|
||||
</TR>
|
||||
|
||||
<TR>
|
||||
<TD><tt>Reference</tt></TD>
|
||||
<TD>The <tt>reference</tt> type of the resulting iterator, and in
|
||||
particular, the result type of <tt>operator*()</tt>. Typically the default for
|
||||
this parameter is the appropriate type.<br> <b>Default:</b> If
|
||||
<tt>Value</tt> is supplied, <tt>Value&</tt> is used. Otherwise
|
||||
<tt>std::iterator_traits<BaseIterator>::reference</tt> is
|
||||
used.</TD>
|
||||
</TR>
|
||||
|
||||
<TR>
|
||||
<TD><tt>Pointer</tt></TD>
|
||||
<TD>The <tt>pointer</tt> type of the resulting iterator, and in
|
||||
particular, the result type of <tt>operator->()</tt>.
|
||||
Typically the default for
|
||||
this parameter is the appropriate type.<br>
|
||||
<b>Default:</b> If <tt>Value</tt> was supplied, then <tt>Value*</tt>,
|
||||
otherwise <tt>std::iterator_traits<BaseIterator>::pointer</tt>.</TD>
|
||||
</TR>
|
||||
|
||||
|
||||
<TR>
|
||||
<TD><tt>Category</tt></TD>
|
||||
<TD>The <tt>iterator_category</tt> type for the resulting iterator.
|
||||
Typically the
|
||||
default for this parameter is the appropriate type. If you override
|
||||
this parameter, do not use <tt>bidirectional_iterator_tag</tt>
|
||||
because filter iterators can not go in reverse.<br>
|
||||
<b>Default:</b> <tt>std::iterator_traits<BaseIterator>::iterator_category</tt></TD>
|
||||
</TR>
|
||||
|
||||
<TR>
|
||||
<TD><tt>Distance</tt></TD>
|
||||
<TD>The <tt>difference_type</tt> for the resulting iterator. Typically the default for
|
||||
this parameter is the appropriate type.<br>
|
||||
<b>Default:</b> <tt>std::iterator_traits<BaseIterator>::difference_type</TD>
|
||||
</TR>
|
||||
|
||||
</table>
|
||||
|
||||
|
||||
<h3>Model of</h3>
|
||||
|
||||
The filter iterator adaptor (the type
|
||||
<tt>filter_iterator_generator<...>::type</tt>) may be a model of <a
|
||||
href="www.sgi.com/tech/stl/InputIterator.html">InputIterator</a> or <a
|
||||
href="www.sgi.com/tech/stl/ForwardIterator.html">ForwardIterator</a>
|
||||
depending on the adapted iterator type.
|
||||
|
||||
|
||||
<h3>Members</h3>
|
||||
|
||||
The filter iterator type implements all of the member functions and
|
||||
operators required of the <a
|
||||
href="http://www.sgi.com/tech/stl/ForwardIterator.html">ForwardIterator</a>
|
||||
concept. In addition it has the following constructor:
|
||||
|
||||
<pre>filter_iterator_generator::type(const BaseIterator& it, const Policies& p = Policies())</pre>
|
||||
|
||||
<p>
|
||||
The policies type has only one public function, which is its constructor:
|
||||
|
||||
<pre>filter_iterator_generator::policies_type(const Predicate& p, const BaseIterator& end)</pre>
|
||||
|
||||
<p>
|
||||
<hr>
|
||||
<p>
|
||||
|
||||
<h2><a name="make_filter_iterator">The Make Filter Iterator Function</a></h2>
|
||||
|
||||
<pre>
|
||||
template <class Predicate, class BaseIterator>
|
||||
typename detail::filter_generator<Predicate, BaseIterator>::type
|
||||
make_filter_iterator(BaseIterator first, BaseIterator last, const Predicate& p = Predicate())
|
||||
</pre>
|
||||
|
||||
This function provides a convenient way to create filter iterators.
|
||||
|
||||
<h3>Example</h3>
|
||||
|
||||
In this example we print out all numbers in the array that are
|
||||
greater than negative two.
|
||||
|
||||
<pre>
|
||||
int main()
|
||||
{
|
||||
int numbers[] = { 0, -1, 4, -3, 5, 8, -2 };
|
||||
const int N = sizeof(numbers)/sizeof(int);
|
||||
|
||||
std::copy(boost::make_filter_iterator(numbers, numbers + N,
|
||||
std::bind2nd(std::greater<int>(), -2)),
|
||||
boost::make_filter_iterator(numbers + N, numbers + N,
|
||||
std::bind2nd(std::greater<int>(), -2)),
|
||||
std::ostream_iterator<int>(std::cout, " "));
|
||||
std::cout << std::endl;
|
||||
|
||||
}
|
||||
</pre>
|
||||
The output is:
|
||||
<pre>
|
||||
0 -1 4 5 8
|
||||
</pre>
|
||||
|
||||
<p>
|
||||
In the next example we print the positive numbers using the
|
||||
<tt>make_filter_iterator()</tt> function.
|
||||
|
||||
<pre>
|
||||
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;
|
||||
}
|
||||
</pre>
|
||||
The output is:
|
||||
<pre>
|
||||
4 5 8
|
||||
</pre>
|
||||
|
||||
|
||||
<h3>Notes</h3>
|
||||
|
||||
<a name="1">[1]</a> If the compiler does not support partial
|
||||
specialization and the wrapped iterator type is a builtin pointer then
|
||||
the <tt>Value</tt> type must be explicitly specified (don't use the
|
||||
default).
|
||||
|
||||
|
||||
<hr>
|
||||
<p>Revised <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %b %Y" startspan -->18 Feb 2001<!--webbot bot="Timestamp" endspan i-checksum="14389" --></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 "as is"
|
||||
without express or implied warranty, and with no claim as to its suitability for
|
||||
any purpose.</p>
|
||||
|
||||
</body>
|
||||
|
||||
</html>
|
||||
464
iterator_adaptor_test.cpp
Normal file
464
iterator_adaptor_test.cpp
Normal file
@@ -0,0 +1,464 @@
|
||||
// Demonstrate and test boost/operators.hpp on std::iterators -------------//
|
||||
|
||||
// (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.
|
||||
|
||||
// See http://www.boost.org for most recent version including documentation.
|
||||
|
||||
// Revision History
|
||||
// 04 Mar 01 Workaround for Borland (Dave Abrahams)
|
||||
// 19 Feb 01 Take adavantage of improved iterator_traits to do more tests
|
||||
// on MSVC. Hack around an MSVC-with-STLport internal compiler
|
||||
// error. (David Abrahams)
|
||||
// 11 Feb 01 Added test of operator-> for forward and input iterators.
|
||||
// (Jeremy Siek)
|
||||
// 11 Feb 01 Borland fixes (David Abrahams)
|
||||
// 10 Feb 01 Use new adaptors interface. (David Abrahams)
|
||||
// 10 Feb 01 Use new filter_ interface. (David Abrahams)
|
||||
// 09 Feb 01 Use new reverse_ and indirect_ interfaces. Replace
|
||||
// BOOST_NO_STD_ITERATOR_TRAITS with
|
||||
// BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION to prove we've
|
||||
// normalized to core compiler capabilities (David Abrahams)
|
||||
// 08 Feb 01 Use Jeremy's new make_reverse_iterator form; add more
|
||||
// comprehensive testing. Force-decay array function arguments to
|
||||
// pointers.
|
||||
// 07 Feb 01 Added tests for the make_xxx_iterator() helper functions.
|
||||
// (Jeremy Siek)
|
||||
// 07 Feb 01 Replaced use of xxx_pair_generator with xxx_generator where
|
||||
// possible (which was all but the projection iterator).
|
||||
// (Jeremy Siek)
|
||||
// 06 Feb 01 Removed now-defaulted template arguments where possible
|
||||
// Updated names to correspond to new generator naming convention.
|
||||
// Added a trivial test for make_transform_iterator().
|
||||
// Gave traits for const iterators a mutable value_type, per std.
|
||||
// Resurrected my original tests for indirect iterators.
|
||||
// (David Abrahams)
|
||||
// 04 Feb 01 Fix for compilers without standard iterator_traits
|
||||
// (David Abrahams)
|
||||
// 13 Jun 00 Added const version of the iterator tests (Jeremy Siek)
|
||||
// 12 Dec 99 Initial version with iterator operators (Jeremy Siek)
|
||||
|
||||
#include <boost/config.hpp>
|
||||
#include <iostream>
|
||||
|
||||
#include <algorithm>
|
||||
#include <functional>
|
||||
|
||||
#include <boost/iterator_adaptors.hpp>
|
||||
#include <boost/pending/iterator_tests.hpp>
|
||||
#include <boost/pending/integer_range.hpp>
|
||||
#include <boost/concept_archetype.hpp>
|
||||
#include <stdlib.h>
|
||||
#include <vector>
|
||||
#include <deque>
|
||||
#include <set>
|
||||
|
||||
struct my_iterator_tag : public std::random_access_iterator_tag { };
|
||||
|
||||
using boost::dummyT;
|
||||
|
||||
struct my_iter_traits {
|
||||
typedef dummyT value_type;
|
||||
typedef dummyT* pointer;
|
||||
typedef dummyT& reference;
|
||||
typedef my_iterator_tag iterator_category;
|
||||
typedef std::ptrdiff_t difference_type;
|
||||
};
|
||||
|
||||
struct my_const_iter_traits {
|
||||
typedef dummyT value_type;
|
||||
typedef const dummyT* pointer;
|
||||
typedef const dummyT& reference;
|
||||
typedef my_iterator_tag iterator_category;
|
||||
typedef std::ptrdiff_t difference_type;
|
||||
};
|
||||
|
||||
typedef boost::iterator_adaptor<dummyT*,
|
||||
boost::default_iterator_policies, dummyT> my_iterator;
|
||||
|
||||
typedef boost::iterator_adaptor<const dummyT*,
|
||||
boost::default_iterator_policies, const dummyT> const_my_iterator;
|
||||
|
||||
|
||||
struct mult_functor {
|
||||
typedef int result_type;
|
||||
typedef int argument_type;
|
||||
// Functors used with transform_iterator must be
|
||||
// DefaultConstructible, as the transform_iterator must be
|
||||
// DefaultConstructible to satisfy the requirements for
|
||||
// TrivialIterator.
|
||||
mult_functor() { }
|
||||
mult_functor(int aa) : a(aa) { }
|
||||
int operator()(int b) const { return a * b; }
|
||||
int a;
|
||||
};
|
||||
|
||||
template <class Pair>
|
||||
struct select1st_
|
||||
: public std::unary_function<Pair, typename Pair::first_type>
|
||||
{
|
||||
const typename Pair::first_type& operator()(const Pair& x) const {
|
||||
return x.first;
|
||||
}
|
||||
typename Pair::first_type& operator()(Pair& x) const {
|
||||
return x.first;
|
||||
}
|
||||
};
|
||||
|
||||
struct one_or_four {
|
||||
bool operator()(dummyT x) const {
|
||||
return x.foo() == 1 || x.foo() == 4;
|
||||
}
|
||||
};
|
||||
|
||||
typedef std::deque<int> storage;
|
||||
typedef std::deque<int*> pointer_deque;
|
||||
typedef std::set<storage::iterator> iterator_set;
|
||||
|
||||
void more_indirect_iterator_tests()
|
||||
{
|
||||
// For some reason all heck breaks loose in the compiler under these conditions.
|
||||
#if !defined(BOOST_MSVC) || !defined(__STL_DEBUG)
|
||||
storage store(1000);
|
||||
std::generate(store.begin(), store.end(), rand);
|
||||
|
||||
pointer_deque ptr_deque;
|
||||
iterator_set iter_set;
|
||||
|
||||
for (storage::iterator p = store.begin(); p != store.end(); ++p)
|
||||
{
|
||||
ptr_deque.push_back(&*p);
|
||||
iter_set.insert(p);
|
||||
}
|
||||
|
||||
typedef boost::indirect_iterator_pair_generator<
|
||||
pointer_deque::iterator
|
||||
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
, int
|
||||
#endif
|
||||
> IndirectDeque;
|
||||
|
||||
IndirectDeque::iterator db(ptr_deque.begin());
|
||||
IndirectDeque::iterator de(ptr_deque.end());
|
||||
assert(static_cast<std::size_t>(de - db) == store.size());
|
||||
assert(db + store.size() == de);
|
||||
IndirectDeque::const_iterator dci(db);
|
||||
assert(db == dci);
|
||||
assert(dci == db);
|
||||
assert(dci != de);
|
||||
assert(dci < de);
|
||||
assert(dci <= de);
|
||||
assert(de >= dci);
|
||||
assert(de > dci);
|
||||
dci = de;
|
||||
assert(dci == de);
|
||||
|
||||
boost::random_access_iterator_test(db + 1, store.size() - 1, boost::next(store.begin()));
|
||||
|
||||
*db = 999;
|
||||
assert(store.front() == 999);
|
||||
|
||||
typedef boost::indirect_iterator_generator<
|
||||
iterator_set::iterator
|
||||
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
, int
|
||||
#endif
|
||||
>::type indirect_set_iterator;
|
||||
|
||||
typedef boost::indirect_iterator_generator<
|
||||
iterator_set::iterator,
|
||||
const int
|
||||
>::type const_indirect_set_iterator;
|
||||
|
||||
indirect_set_iterator sb(iter_set.begin());
|
||||
indirect_set_iterator se(iter_set.end());
|
||||
const_indirect_set_iterator sci(iter_set.begin());
|
||||
assert(sci == sb);
|
||||
assert(sci != se);
|
||||
sci = se;
|
||||
assert(sci == se);
|
||||
|
||||
*boost::prior(se) = 888;
|
||||
assert(store.back() == 888);
|
||||
assert(std::equal(sb, se, store.begin()));
|
||||
|
||||
boost::bidirectional_iterator_test(boost::next(sb), store[1], store[2]);
|
||||
assert(std::equal(db, de, store.begin()));
|
||||
#endif
|
||||
}
|
||||
|
||||
int
|
||||
main()
|
||||
{
|
||||
dummyT array[] = { dummyT(0), dummyT(1), dummyT(2),
|
||||
dummyT(3), dummyT(4), dummyT(5) };
|
||||
const int N = sizeof(array)/sizeof(dummyT);
|
||||
|
||||
// sanity check, if this doesn't pass the test is buggy
|
||||
boost::random_access_iterator_test(array,N,array);
|
||||
|
||||
// Check that the policy concept checks and the default policy
|
||||
// implementation match up.
|
||||
boost::function_requires<
|
||||
boost::RandomAccessIteratorPoliciesConcept<
|
||||
boost::default_iterator_policies, int*,
|
||||
boost::iterator<std::random_access_iterator_tag, int, std::ptrdiff_t,
|
||||
int*, int&>
|
||||
> >();
|
||||
|
||||
// Test the iterator_adaptor
|
||||
{
|
||||
my_iterator i(array);
|
||||
boost::random_access_iterator_test(i, N, array);
|
||||
|
||||
const_my_iterator j(array);
|
||||
boost::random_access_iterator_test(j, N, array);
|
||||
boost::const_nonconst_iterator_test(i, ++j);
|
||||
}
|
||||
|
||||
// Test transform_iterator
|
||||
{
|
||||
int x[N], y[N];
|
||||
for (int k = 0; k < N; ++k)
|
||||
x[k] = k;
|
||||
std::copy(x, x + N, y);
|
||||
|
||||
for (int k2 = 0; k2 < N; ++k2)
|
||||
x[k2] = x[k2] * 2;
|
||||
|
||||
boost::transform_iterator_generator<mult_functor, int*>::type
|
||||
i(y, mult_functor(2));
|
||||
boost::input_iterator_test(i, x[0], x[1]);
|
||||
boost::input_iterator_test(boost::make_transform_iterator(&y[0], mult_functor(2)), x[0], x[1]);
|
||||
}
|
||||
|
||||
// Test indirect_iterator_generator
|
||||
{
|
||||
dummyT* ptr[N];
|
||||
for (int k = 0; k < N; ++k)
|
||||
ptr[k] = array + k;
|
||||
|
||||
typedef boost::indirect_iterator_generator<dummyT**
|
||||
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
, dummyT
|
||||
#endif
|
||||
>::type indirect_iterator;
|
||||
|
||||
typedef boost::indirect_iterator_generator<dummyT**, const dummyT>::type const_indirect_iterator;
|
||||
|
||||
indirect_iterator i(ptr);
|
||||
boost::random_access_iterator_test(i, N, array);
|
||||
|
||||
#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
boost::random_access_iterator_test(boost::make_indirect_iterator(ptr), N, array);
|
||||
#endif
|
||||
|
||||
// check operator->
|
||||
assert((*i).m_x == i->foo());
|
||||
|
||||
const_indirect_iterator j(ptr);
|
||||
boost::random_access_iterator_test(j, N, array);
|
||||
|
||||
dummyT*const* const_ptr = ptr;
|
||||
|
||||
#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
boost::random_access_iterator_test(boost::make_indirect_iterator(const_ptr), N, array);
|
||||
#endif
|
||||
boost::const_nonconst_iterator_test(i, ++j);
|
||||
|
||||
more_indirect_iterator_tests();
|
||||
}
|
||||
|
||||
// Test projection_iterator_pair_generator
|
||||
{
|
||||
typedef std::pair<dummyT,dummyT> Pair;
|
||||
Pair pair_array[N];
|
||||
for (int k = 0; k < N; ++k)
|
||||
pair_array[k].first = array[k];
|
||||
|
||||
typedef boost::projection_iterator_pair_generator<select1st_<Pair>,
|
||||
Pair*, const Pair*
|
||||
> Projection;
|
||||
|
||||
Projection::iterator i(pair_array);
|
||||
boost::random_access_iterator_test(i, N, array);
|
||||
|
||||
boost::random_access_iterator_test(boost::make_projection_iterator(pair_array, select1st_<Pair>()), N, array);
|
||||
boost::random_access_iterator_test(boost::make_projection_iterator< select1st_<Pair> >(pair_array), N, array);
|
||||
|
||||
Projection::const_iterator j(pair_array);
|
||||
boost::random_access_iterator_test(j, N, array);
|
||||
|
||||
boost::random_access_iterator_test(boost::make_const_projection_iterator(pair_array, select1st_<Pair>()), N, array);
|
||||
boost::random_access_iterator_test(boost::make_const_projection_iterator<select1st_<Pair> >(pair_array), N, array);
|
||||
|
||||
boost::const_nonconst_iterator_test(i, ++j);
|
||||
}
|
||||
|
||||
// Test reverse_iterator_generator
|
||||
{
|
||||
dummyT reversed[N];
|
||||
std::copy(array, array + N, reversed);
|
||||
std::reverse(reversed, reversed + N);
|
||||
|
||||
typedef boost::reverse_iterator_generator<dummyT*
|
||||
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
, dummyT
|
||||
#endif
|
||||
>::type reverse_iterator;
|
||||
|
||||
reverse_iterator i(reversed + N);
|
||||
boost::random_access_iterator_test(i, N, array);
|
||||
|
||||
#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
boost::random_access_iterator_test(boost::make_reverse_iterator(reversed + N), N, array);
|
||||
#endif
|
||||
|
||||
typedef boost::reverse_iterator_generator<const dummyT*
|
||||
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
, const dummyT
|
||||
#endif
|
||||
>::type const_reverse_iterator;
|
||||
|
||||
const_reverse_iterator j(reversed + N);
|
||||
boost::random_access_iterator_test(j, N, array);
|
||||
|
||||
const dummyT* const_reversed = reversed;
|
||||
|
||||
#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
boost::random_access_iterator_test(boost::make_reverse_iterator(const_reversed + N), N, array);
|
||||
#endif
|
||||
|
||||
boost::const_nonconst_iterator_test(i, ++j);
|
||||
}
|
||||
|
||||
// Test reverse_iterator_generator again, with traits fully deducible on all platforms
|
||||
{
|
||||
std::deque<dummyT> reversed_container;
|
||||
std::reverse_copy(array, array + N, std::back_inserter(reversed_container));
|
||||
const std::deque<dummyT>::iterator reversed = reversed_container.begin();
|
||||
|
||||
|
||||
typedef boost::reverse_iterator_generator<
|
||||
std::deque<dummyT>::iterator>::type reverse_iterator;
|
||||
typedef boost::reverse_iterator_generator<
|
||||
std::deque<dummyT>::const_iterator, const dummyT>::type const_reverse_iterator;
|
||||
|
||||
// MSVC/STLport gives an INTERNAL COMPILER ERROR when any computation
|
||||
// (e.g. "reversed + N") is used in the constructor below.
|
||||
const std::deque<dummyT>::iterator finish = reversed_container.end();
|
||||
reverse_iterator i(finish);
|
||||
|
||||
boost::random_access_iterator_test(i, N, array);
|
||||
boost::random_access_iterator_test(boost::make_reverse_iterator(reversed + N), N, array);
|
||||
|
||||
const_reverse_iterator j = reverse_iterator(finish);
|
||||
boost::random_access_iterator_test(j, N, array);
|
||||
|
||||
const std::deque<dummyT>::const_iterator const_reversed = reversed;
|
||||
boost::random_access_iterator_test(boost::make_reverse_iterator(const_reversed + N), N, array);
|
||||
|
||||
// Many compilers' builtin deque iterators don't interoperate well, though
|
||||
// STLport fixes that problem.
|
||||
#if defined(__SGI_STL_PORT) || !defined(__GNUC__) && !defined(__BORLANDC__) && !defined(BOOST_MSVC)
|
||||
boost::const_nonconst_iterator_test(i, ++j);
|
||||
#endif
|
||||
}
|
||||
|
||||
// Test integer_range's iterators
|
||||
{
|
||||
int int_array[] = { 0, 1, 2, 3, 4, 5 };
|
||||
boost::integer_range<int> r(0, 5);
|
||||
boost::random_access_iterator_test(r.begin(), r.size(), int_array);
|
||||
}
|
||||
|
||||
// Test filter iterator
|
||||
{
|
||||
// Using typedefs for filter_gen::type and filter_gen::policies_type
|
||||
// confused Borland terribly.
|
||||
typedef boost::detail::non_bidirectional_category<dummyT*>::type category;
|
||||
|
||||
typedef ::boost::filter_iterator_generator<one_or_four, dummyT*
|
||||
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
, dummyT
|
||||
#endif
|
||||
> filter_iter_gen;
|
||||
|
||||
#ifndef __BORLANDC__
|
||||
typedef filter_iter_gen::type filter_iter;
|
||||
#else
|
||||
# define filter_iter filter_iter_gen::type // Borland has a problem with the above
|
||||
#endif
|
||||
filter_iter i(array, filter_iter::policies_type(one_or_four(), array + N));
|
||||
boost::forward_iterator_test(i, dummyT(1), dummyT(4));
|
||||
|
||||
enum { is_forward = boost::is_same<
|
||||
filter_iter::iterator_category,
|
||||
std::forward_iterator_tag>::value };
|
||||
BOOST_STATIC_ASSERT(is_forward);
|
||||
|
||||
// On compilers not supporting partial specialization, we can do more type
|
||||
// deduction with deque iterators than with pointers... unless the library
|
||||
// is broken ;-(
|
||||
#if !defined(BOOST_MSVC) || defined(__SGI_STL_PORT)
|
||||
std::deque<dummyT> array2;
|
||||
std::copy(array+0, array+N, std::back_inserter(array2));
|
||||
boost::forward_iterator_test(
|
||||
boost::make_filter_iterator(array2.begin(), array2.end(), one_or_four()),
|
||||
dummyT(1), dummyT(4));
|
||||
|
||||
boost::forward_iterator_test(
|
||||
boost::make_filter_iterator<one_or_four>(array2.begin(), array2.end()),
|
||||
dummyT(1), dummyT(4));
|
||||
#endif
|
||||
|
||||
#if !defined(BOOST_MSVC) // This just freaks MSVC out completely
|
||||
boost::forward_iterator_test(
|
||||
boost::make_filter_iterator<one_or_four>(
|
||||
boost::make_reverse_iterator(array2.end()),
|
||||
boost::make_reverse_iterator(array2.begin())
|
||||
),
|
||||
dummyT(4), dummyT(1));
|
||||
#endif
|
||||
|
||||
#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
|
||||
boost::forward_iterator_test(
|
||||
boost::make_filter_iterator(array+0, array+N, one_or_four()),
|
||||
dummyT(1), dummyT(4));
|
||||
|
||||
boost::forward_iterator_test(
|
||||
boost::make_filter_iterator<one_or_four>(array, array + N),
|
||||
dummyT(1), dummyT(4));
|
||||
|
||||
#endif
|
||||
}
|
||||
|
||||
// check operator-> with a forward iterator
|
||||
{
|
||||
boost::forward_iterator_archetype<dummyT> forward_iter;
|
||||
typedef boost::iterator_adaptor<boost::forward_iterator_archetype<dummyT>,
|
||||
boost::default_iterator_policies,
|
||||
dummyT, const dummyT&, const dummyT*,
|
||||
std::forward_iterator_tag, std::ptrdiff_t> adaptor_type;
|
||||
adaptor_type i(forward_iter);
|
||||
if (0) // don't do this, just make sure it compiles
|
||||
assert((*i).m_x == i->foo());
|
||||
}
|
||||
// check operator-> with an input iterator
|
||||
{
|
||||
boost::input_iterator_archetype<dummyT> input_iter;
|
||||
typedef boost::iterator_adaptor<boost::input_iterator_archetype<dummyT>,
|
||||
boost::default_iterator_policies,
|
||||
dummyT, const dummyT&, const dummyT*,
|
||||
std::input_iterator_tag, std::ptrdiff_t> adaptor_type;
|
||||
adaptor_type i(input_iter);
|
||||
if (0) // don't do this, just make sure it compiles
|
||||
assert((*i).m_x == i->foo());
|
||||
}
|
||||
|
||||
std::cout << "test successful " << std::endl;
|
||||
return 0;
|
||||
}
|
||||
331
reverse_iterator.htm
Normal file
331
reverse_iterator.htm
Normal file
@@ -0,0 +1,331 @@
|
||||
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
|
||||
|
||||
<html>
|
||||
<head>
|
||||
<meta name="generator" content="HTML Tidy, see www.w3.org">
|
||||
<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>Reverse 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>Reverse Iterator Adaptor</h1>
|
||||
Defined in header <a href=
|
||||
"../../boost/iterator_adaptors.hpp">boost/iterator_adaptors.hpp</a>
|
||||
|
||||
<p>The reverse iterator adaptor flips the direction of a base iterator's
|
||||
motion. Invoking <tt>operator++()</tt> moves the base iterator backward and
|
||||
invoking <tt>operator--()</tt> moves the base iterator forward. The Boost
|
||||
reverse iterator adaptor is better to use than the
|
||||
<tt>std::reverse_iterator</tt> class in situations where pairs of
|
||||
mutable/constant iterators are needed (e.g., in containers) because
|
||||
comparisons and conversions between the mutable and const versions are
|
||||
implemented correctly.
|
||||
|
||||
<h2>Synopsis</h2>
|
||||
<pre>
|
||||
namespace boost {
|
||||
template <class <a href=
|
||||
"http://www.sgi.com/tech/stl/BidirectionalIterator.html">BidirectionalIterator</a>,
|
||||
class Value, class Reference, class Pointer, class Category, class Distance>
|
||||
struct reverse_iterator_generator;
|
||||
|
||||
template <class <a href=
|
||||
"http://www.sgi.com/tech/stl/BidirectionalIterator.html">BidirectionalIterator</a>>
|
||||
typename reverse_iterator_generator<BidirectionalIterator>::type
|
||||
make_reverse_iterator(BidirectionalIterator base)
|
||||
}
|
||||
</pre>
|
||||
<hr>
|
||||
|
||||
<h2><a name="reverse_iterator_generator">The Reverse Iterator Type
|
||||
Generator</a></h2>
|
||||
The <tt>reverse_iterator_generator</tt> template is a <a href=
|
||||
"../../more/generic_programming.html#type_generator">generator</a> of
|
||||
reverse iterator types. The main template parameter for this class is the
|
||||
base <tt>BidirectionalIterator</tt> type that is being adapted. In most
|
||||
cases the associated types of the base iterator can be deduced using
|
||||
<tt>std::iterator_traits</tt>, but in some situations the user may want to
|
||||
override these types, so there are also template parameters for the base
|
||||
iterator's associated types.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
template <class <a href=
|
||||
"http://www.sgi.com/tech/stl/BidirectionalIterator.html">BidirectionalIterator</a>,
|
||||
class Value, class Reference, class Pointer, class Category, class Distance>
|
||||
class reverse_iterator_generator
|
||||
{
|
||||
public:
|
||||
typedef <tt><a href=
|
||||
"./iterator_adaptors.htm#iterator_adaptor">iterator_adaptor</a><...></tt> type; // the resulting reverse iterator type
|
||||
};
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h3>Example</h3>
|
||||
In this example we sort a sequence of letters and then output the sequence
|
||||
in descending order using reverse iterators.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
#include <boost/config.hpp>
|
||||
#include <iostream>
|
||||
#include <algorithm>
|
||||
#include <boost/iterator_adaptors.hpp>
|
||||
|
||||
int main(int, char*[])
|
||||
{
|
||||
char letters[] = "hello world!";
|
||||
const int N = sizeof(letters)/sizeof(char) - 1;
|
||||
std::cout << "original sequence of letters:\t"
|
||||
<< letters << std::endl;
|
||||
|
||||
std::sort(letters, letters + N);
|
||||
|
||||
// Use reverse_iterator_generator to print a sequence
|
||||
// of letters in reverse order.
|
||||
|
||||
boost::reverse_iterator_generator<char*>::type
|
||||
reverse_letters_first(letters + N),
|
||||
reverse_letters_last(letters);
|
||||
|
||||
std::cout << "letters in descending order:\t";
|
||||
std::copy(reverse_letters_first, reverse_letters_last,
|
||||
std::ostream_iterator<char>(std::cout));
|
||||
std::cout << std::endl;
|
||||
|
||||
// to be continued...
|
||||
</pre>
|
||||
</blockquote>
|
||||
The output is:
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
original sequence of letters: hello world!
|
||||
letters in descending order: wroolllhed!
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h3>Template Parameters</h3>
|
||||
|
||||
<table border>
|
||||
<tr>
|
||||
<th>Parameter
|
||||
|
||||
<th>Description
|
||||
|
||||
<tr>
|
||||
<td><tt><a href=
|
||||
"http://www.sgi.com/tech/stl/BidirectionalIterator.html">BidirectionalIterator</a></tt>
|
||||
|
||||
|
||||
<td>The iterator type being wrapped.
|
||||
|
||||
<tr>
|
||||
<td><tt>Value</tt>
|
||||
|
||||
<td>The value-type of the base iterator and the resulting reverse
|
||||
iterator.<br>
|
||||
<b>Default:</b><tt>std::iterator_traits<BidirectionalIterator>::value_type</tt>
|
||||
|
||||
|
||||
<tr>
|
||||
<td><tt>Reference</tt>
|
||||
|
||||
<td>The <tt>reference</tt> type of the resulting iterator, and in
|
||||
particular, the result type of <tt>operator*()</tt>.<br>
|
||||
<b>Default:</b> If <tt>Value</tt> is supplied, <tt>Value&</tt> is
|
||||
used. Otherwise
|
||||
<tt>std::iterator_traits<BidirectionalIterator>::reference</tt>
|
||||
is used.
|
||||
|
||||
<tr>
|
||||
<td><tt>Pointer</tt>
|
||||
|
||||
<td>The <tt>pointer</tt> type of the resulting iterator, and in
|
||||
particular, the result type of <tt>operator->()</tt>.<br>
|
||||
<b>Default:</b> If <tt>Value</tt> was supplied, then <tt>Value*</tt>,
|
||||
otherwise
|
||||
<tt>std::iterator_traits<BidirectionalIterator>::pointer</tt>.
|
||||
|
||||
<tr>
|
||||
<td><tt>Category</tt>
|
||||
|
||||
<td>The <tt>iterator_category</tt> type for the resulting iterator.<br>
|
||||
<b>Default:</b>
|
||||
<tt>std::iterator_traits<BidirectionalIterator>::iterator_category</tt>
|
||||
|
||||
|
||||
<tr>
|
||||
<td><tt>Distance</tt>
|
||||
|
||||
<td>The <tt>difference_type</tt> for the resulting iterator.<br>
|
||||
<b>Default:</b>
|
||||
<tt>std::iterator_traits<BidirectionalIterator&gt::difference_type</tt>
|
||||
|
||||
</table>
|
||||
|
||||
<h3>Concept Model</h3>
|
||||
The indirect iterator will model whichever <a href=
|
||||
"http://www.sgi.com/tech/stl/Iterators.html">standard iterator concept
|
||||
category</a> is modeled by the base iterator. Thus, if the base iterator is
|
||||
a model of <a href=
|
||||
"http://www.sgi.com/tech/stl/RandomAccessIterator.html">Random Access
|
||||
Iterator</a> then so is the resulting indirect iterator. If the base
|
||||
iterator models a more restrictive concept, the resulting indirect iterator
|
||||
will model the same concept. The base iterator must be at least a <a href=
|
||||
"http://www.sgi.com/tech/stl/BidirectionalIterator.html">Bidirectional
|
||||
Iterator</a>
|
||||
|
||||
<h3>Members</h3>
|
||||
The reverse iterator type implements the member functions and operators
|
||||
required of the <a href=
|
||||
"http://www.sgi.com/tech/stl/RandomAccessIterator.html">Random Access
|
||||
Iterator</a> concept. In addition it has the following constructor:
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
reverse_iterator_generator::type(const BidirectionalIterator& it)
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
|
||||
<br>
|
||||
<br>
|
||||
|
||||
<hr>
|
||||
|
||||
<p>
|
||||
|
||||
<h2><a name="make_reverse_iterator">The Reverse Iterator Object
|
||||
Generator</a></h2>
|
||||
The <tt>make_reverse_iterator()</tt> function provides a more convenient
|
||||
way to create reverse iterator objects. The function saves the user the
|
||||
trouble of explicitly writing out the iterator types.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
template <class BidirectionalIterator>
|
||||
typename reverse_iterator_generator<BidirectionalIterator>::type
|
||||
make_reverse_iterator(BidirectionalIterator base);
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h3>Example</h3>
|
||||
In this part of the example we use <tt>make_reverse_iterator()</tt> to
|
||||
print the sequence of letters in reverse-reverse order, which is the
|
||||
original order.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
// continuing from the previous example...
|
||||
|
||||
std::cout << "letters in ascending 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;
|
||||
|
||||
return 0;
|
||||
}
|
||||
</pre>
|
||||
</blockquote>
|
||||
The output is:
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
letters in ascending order: !dehllloorw
|
||||
</pre>
|
||||
</blockquote>
|
||||
<hr>
|
||||
|
||||
<h2><a name="interactions">Constant/Mutable Iterator Interactions</a></h2>
|
||||
|
||||
<p>One failing of the standard <tt><a
|
||||
href="http://www.sgi.com/tech/stl/ReverseIterator.html">reverse_iterator</a></tt>
|
||||
adaptor is that it doesn't properly support interactions between adapted
|
||||
<tt>const</tt> and non-<tt>const</tt> iterators. For example:
|
||||
<blockquote>
|
||||
<pre>
|
||||
#include <vector>
|
||||
|
||||
template <class T> void convert(T x) {}
|
||||
|
||||
// Test interactions of a matched pair of random access iterators
|
||||
template <class Iterator, class ConstIterator>
|
||||
void test_interactions(Iterator i, ConstIterator ci)
|
||||
{
|
||||
bool eq = i == ci; // comparisons
|
||||
bool ne = i != ci;
|
||||
bool lt = i < ci;
|
||||
bool le = i <= ci;
|
||||
bool gt = i > ci;
|
||||
bool ge = i >= ci;
|
||||
std::size_t distance = i - ci; // difference
|
||||
ci = i; // assignment
|
||||
ConstIterator ci2(i); // construction
|
||||
convert<ConstIterator>(i); // implicit conversion
|
||||
}
|
||||
|
||||
void f()
|
||||
{
|
||||
typedef std::vector<int> vec;
|
||||
vec v;
|
||||
const vec& cv;
|
||||
|
||||
test_interactions(v.begin(), cv.begin()); // <font color="#007F00">OK</font>
|
||||
test_interactions(v.rbegin(), cv.rbegin()); // <font color="#FF0000">ERRORS ON EVERY TEST!!</font>
|
||||
</pre>
|
||||
</blockquote>
|
||||
Reverse iterators created with <tt>boost::reverse_iterator_generator</tt> don't have this problem, though:
|
||||
<blockquote>
|
||||
<pre>
|
||||
typedef boost::reverse_iterator_generator<vec::iterator>::type ri;
|
||||
typedef boost::reverse_iterator_generator<vec::const_iterator>::type cri;
|
||||
test_interactions(ri(v.begin()), cri(cv.begin())); // <font color="#007F00">OK!!</font>
|
||||
</pre>
|
||||
</blockquote>
|
||||
Or, more simply,
|
||||
<blockquote>
|
||||
<pre>
|
||||
test_interactions(
|
||||
boost::make_reverse_iterator(v.begin()),
|
||||
boost::make_reverse_iterator(cv.begin())); // <font color="#007F00">OK!!</font>
|
||||
}
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<p>If you are wondering why there is no
|
||||
<tt>reverse_iterator_pair_generator</tt> in the manner of <tt><a
|
||||
href="projection_iterator.htm#projection_iterator_pair_generator">projection_iterator_pair_generator</a></tt>,
|
||||
the answer is simple: we tried it, but found that in practice it took
|
||||
<i>more</i> typing to use <tt>reverse_iterator_pair_generator</tt> than to
|
||||
simply use <tt>reverse_iterator_generator</tt> twice!<br><br>
|
||||
|
||||
<hr>
|
||||
|
||||
|
||||
<p>Revised
|
||||
<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %b %Y" startspan -->26 Feb 2001<!--webbot bot="Timestamp" endspan i-checksum="14386" -->
|
||||
|
||||
|
||||
<p>© 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 "as is" without express or
|
||||
implied warranty, and with no claim as to its suitability for any purpose.
|
||||
<!-- LocalWords: html charset alt gif hpp BidirectionalIterator const namespace struct
|
||||
-->
|
||||
|
||||
<!-- LocalWords: ConstPointer ConstReference typename iostream int abcdefg
|
||||
-->
|
||||
<!-- LocalWords: sizeof PairGen pre Siek wroolllhed dehllloorw
|
||||
-->
|
||||
</body>
|
||||
</html>
|
||||
|
||||
Reference in New Issue
Block a user