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filter_iterator.htm
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filter_iterator.htm
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<html>
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|
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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>
|
||||
</head>
|
||||
|
||||
<body bgcolor="#FFFFFF" text="#000000">
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|
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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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|
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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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|
||||
|
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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
|
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predicate is applied to an element, if it returns <tt>true</tt> then
|
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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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|
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|
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<h2>Synopsis</h2>
|
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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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|
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<hr>
|
||||
|
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<h2><a name="filter_iterator_generator">The Filter Iterator Type
|
||||
Generator</a></h2>
|
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|
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The class <tt>filter_iterator_generator</tt> is a helper class whose
|
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purpose is to construct a filter iterator type. The template
|
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parameters for this class are the <tt>Predicate</tt> function object
|
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type and the <tt>BaseIterator</tt> type that is being wrapped. In
|
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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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|
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<pre>
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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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{
|
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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
|
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positive integers in an array.
|
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|
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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>
|
||||
|
||||
|
||||
<h3>Template Parameters</h3>
|
||||
|
||||
<Table border>
|
||||
<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>
|
||||
@@ -1,443 +0,0 @@
|
||||
<!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>Indirect 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>Indirect Iterator Adaptor</h1>
|
||||
Defined in header <a href=
|
||||
"../../boost/iterator_adaptors.hpp">boost/iterator_adaptors.hpp</a>
|
||||
|
||||
<p>The indirect iterator adaptor augments an iterator by applying an
|
||||
<b>extra</b> dereference inside of <tt>operator*()</tt>. For example, this
|
||||
iterator makes it possible to view a container of pointers or
|
||||
smart-pointers (e.g. <tt>std::list<boost::shared_ptr<foo>
|
||||
></tt>) as if it were a container of the pointed-to type. The following
|
||||
<b>pseudo-code</b> shows the basic idea of the indirect iterator:
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
// inside a hypothetical indirect_iterator class...
|
||||
typedef std::iterator_traits<BaseIterator>::value_type Pointer;
|
||||
typedef std::iterator_traits<Pointer>::reference reference;
|
||||
|
||||
reference indirect_iterator::operator*() const {
|
||||
return **this->base_iterator;
|
||||
}
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h2>Synopsis</h2>
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
namespace boost {
|
||||
template <class BaseIterator,
|
||||
class Value, class Reference, class Category, class Pointer>
|
||||
struct indirect_iterator_generator;
|
||||
|
||||
template <class BaseIterator,
|
||||
class Value, class Reference, class ConstReference,
|
||||
class Category, class Pointer, class ConstPointer>
|
||||
struct indirect_iterator_pair_generator;
|
||||
|
||||
template <class BaseIterator>
|
||||
typename indirect_iterator_generator<BaseIterator>::type
|
||||
make_indirect_iterator(BaseIterator base)
|
||||
}
|
||||
</pre>
|
||||
</blockquote>
|
||||
<hr>
|
||||
|
||||
<h2><a name="indirect_iterator_generator">The Indirect Iterator Type
|
||||
Generator</a></h2>
|
||||
The <tt>indirect_iterator_generator</tt> template is a <a href=
|
||||
"../../more/generic_programming.html#type_generator">generator</a> of
|
||||
indirect iterator types. The main template parameter for this class is the
|
||||
<tt>BaseIterator</tt> type that is being wrapped. In most cases the type of
|
||||
the elements being pointed to can be deduced using
|
||||
<tt>std::iterator_traits</tt>, but in some situations the user may want to
|
||||
override this type, so there are also template parameters that allow a user
|
||||
to control the <tt>value_type</tt>, <tt>pointer</tt>, and
|
||||
<tt>reference</tt> types of the resulting iterators.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
template <class BaseIterator,
|
||||
class Value, class Reference, class Pointer>
|
||||
class indirect_iterator_generator
|
||||
{
|
||||
public:
|
||||
typedef <tt><a href=
|
||||
"./iterator_adaptors.htm#iterator_adaptor">iterator_adaptor</a><...></tt> type; // the resulting indirect iterator type
|
||||
};
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h3>Example</h3>
|
||||
This example uses the <tt>indirect_iterator_generator</tt> to create
|
||||
indirect iterators which dereference the pointers stored in the
|
||||
<tt>pointers_to_chars</tt> array to access the <tt>char</tt>s in the
|
||||
<tt>characters</tt> array.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
#include <boost/config.hpp>
|
||||
#include <vector>
|
||||
#include <iostream>
|
||||
#include <iterator>
|
||||
#include <boost/iterator_adaptors.hpp>
|
||||
|
||||
int main(int, char*[])
|
||||
{
|
||||
char characters[] = "abcdefg";
|
||||
const int N = sizeof(characters)/sizeof(char) - 1; // -1 since characters has a null char
|
||||
char* pointers_to_chars[N]; // at the end.
|
||||
for (int i = 0; i < N; ++i)
|
||||
pointers_to_chars[i] = &characters[i];
|
||||
|
||||
boost::indirect_iterator_generator<char**, char>::type
|
||||
indirect_first(pointers_to_chars), indirect_last(pointers_to_chars + N);
|
||||
|
||||
std::copy(indirect_first, indirect_last, std::ostream_iterator<char>(std::cout, ","));
|
||||
std::cout << std::endl;
|
||||
|
||||
// to be continued...
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h3>Template Parameters</h3>
|
||||
|
||||
<table border>
|
||||
<tr>
|
||||
<th>Parameter
|
||||
|
||||
<th>Description
|
||||
|
||||
<tr>
|
||||
<td><tt>BaseIterator</tt>
|
||||
|
||||
<td>The iterator type being wrapped. The <tt>value_type</tt>
|
||||
of the base iterator should itself be dereferenceable.
|
||||
The return type of the <tt>operator*</tt> for the
|
||||
<tt>value_type</tt> should match the <tt>Reference</tt> type.
|
||||
|
||||
<tr>
|
||||
<td><tt>Value</tt>
|
||||
|
||||
<td>The <tt>value_type</tt> of the resulting iterator, unless const. If
|
||||
Value is <tt>const X</tt>, a conforming compiler makes the
|
||||
<tt>value_type</tt> <tt><i>non-</i>const X</tt><a href=
|
||||
"iterator_adaptors.htm#1">[1]</a>. Note that if the default
|
||||
is used for <tt>Value</tt>, then there must be a valid specialization
|
||||
of <tt>iterator_traits</tt> for the value type of the base iterator.
|
||||
<br>
|
||||
<b>Default:</b> <tt>std::iterator_traits<<br>
|
||||
<20> std::iterator_traits<BaseIterator>::value_type
|
||||
>::value_type</tt><a href="#2">[2]</a>
|
||||
|
||||
<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> <tt>Value&</tt>
|
||||
|
||||
<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> <tt>Value*</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<BaseIterator>::iterator_category</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 <a href="#3">[3]</a>.
|
||||
|
||||
<h3>Members</h3>
|
||||
The indirect 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:
|
||||
<pre>
|
||||
explicit indirect_iterator_generator::type(const BaseIterator& it)
|
||||
</pre>
|
||||
<br>
|
||||
<br>
|
||||
|
||||
<hr>
|
||||
|
||||
<p>
|
||||
|
||||
<h2><a name="indirect_iterator_pair_generator">The Indirect Iterator Pair
|
||||
Generator</a></h2>
|
||||
Sometimes a pair of <tt>const</tt>/non-<tt>const</tt> pair of iterators is
|
||||
needed, such as when implementing a container. The
|
||||
<tt>indirect_iterator_pair_generator</tt> class makes it more convenient to
|
||||
create this pair of iterator types.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
template <class BaseIterator,
|
||||
class Value, class Pointer, class Reference,
|
||||
class ConstPointer, class ConstReference>
|
||||
class indirect_iterator_pair_generator
|
||||
{
|
||||
public:
|
||||
typedef <tt><a href=
|
||||
"./iterator_adaptors.htm#iterator_adaptor">iterator_adaptor</a><...></tt> iterator; // the mutable indirect iterator type
|
||||
typedef <tt><a href=
|
||||
"./iterator_adaptors.htm#iterator_adaptor">iterator_adaptor</a><...></tt> const_iterator; // the immutable indirect iterator type
|
||||
};
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h3>Example</h3>
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
// continuing from the last example...
|
||||
|
||||
typedef boost::indirect_iterator_pair_generator<char**,
|
||||
char, char*, char&, const char*, const char&> PairGen;
|
||||
|
||||
char mutable_characters[N];
|
||||
char* pointers_to_mutable_chars[N];
|
||||
for (int i = 0; i < N; ++i)
|
||||
pointers_to_mutable_chars[i] = &mutable_characters[i];
|
||||
|
||||
PairGen::iterator mutable_indirect_first(pointers_to_mutable_chars),
|
||||
mutable_indirect_last(pointers_to_mutable_chars + N);
|
||||
PairGen::const_iterator const_indirect_first(pointers_to_chars),
|
||||
const_indirect_last(pointers_to_chars + N);
|
||||
|
||||
std::transform(const_indirect_first, const_indirect_last,
|
||||
mutable_indirect_first, std::bind1st(std::plus<char>(), 1));
|
||||
|
||||
std::copy(mutable_indirect_first, mutable_indirect_last,
|
||||
std::ostream_iterator<char>(std::cout, ","));
|
||||
std::cout << std::endl;
|
||||
// to be continued...
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<p>The output is:
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
b,c,d,e,f,g,h,
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h3>Template Parameters</h3>
|
||||
|
||||
<table border>
|
||||
<tr>
|
||||
<th>Parameter
|
||||
|
||||
<th>Description
|
||||
|
||||
<tr>
|
||||
<td><tt>BaseIterator</tt>
|
||||
|
||||
<td>The iterator type being wrapped. The <tt>value_type</tt> of the
|
||||
base iterator should itself be dereferenceable.
|
||||
The return type of the <tt>operator*</tt> for the
|
||||
<tt>value_type</tt> should match the <tt>Reference</tt> type.
|
||||
|
||||
<tr>
|
||||
<td><tt>Value</tt>
|
||||
|
||||
<td>The <tt>value_type</tt> of the resulting iterators.
|
||||
If Value is <tt>const X</tt>, a conforming compiler makes the
|
||||
<tt>value_type</tt> <tt><i>non-</i>const X</tt><a href=
|
||||
"iterator_adaptors.htm#1">[1]</a>. Note that if the default
|
||||
is used for <tt>Value</tt>, then there must be a valid
|
||||
specialization of <tt>iterator_traits</tt> for the value type
|
||||
of the base iterator.<br>
|
||||
|
||||
<b>Default:</b> <tt>std::iterator_traits<<br>
|
||||
<20> std::iterator_traits<BaseIterator>::value_type
|
||||
>::value_type</tt><a href="#2">[2]</a>
|
||||
|
||||
<tr>
|
||||
<td><tt>Reference</tt>
|
||||
|
||||
<td>The <tt>reference</tt> type of the resulting <tt>iterator</tt>, and
|
||||
in particular, the result type of its <tt>operator*()</tt>.<br>
|
||||
<b>Default:</b> <tt>Value&</tt>
|
||||
|
||||
<tr>
|
||||
<td><tt>Pointer</tt>
|
||||
|
||||
<td>The <tt>pointer</tt> type of the resulting <tt>iterator</tt>, and
|
||||
in particular, the result type of its <tt>operator->()</tt>.<br>
|
||||
<b>Default:</b> <tt>Value*</tt>
|
||||
|
||||
<tr>
|
||||
<td><tt>ConstReference</tt>
|
||||
|
||||
<td>The <tt>reference</tt> type of the resulting
|
||||
<tt>const_iterator</tt>, and in particular, the result type of its
|
||||
<tt>operator*()</tt>.<br>
|
||||
<b>Default:</b> <tt>const Value&</tt>
|
||||
|
||||
<tr>
|
||||
<td><tt>ConstPointer</tt>
|
||||
|
||||
<td>The <tt>pointer</tt> type of the resulting <tt>const_iterator</tt>,
|
||||
and in particular, the result type of its <tt>operator->()</tt>.<br>
|
||||
<b>Default:</b> <tt>const Value*</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<BaseIterator>::iterator_category</tt>
|
||||
</table>
|
||||
|
||||
<h3>Concept Model</h3>
|
||||
|
||||
The indirect iterators 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 are the resulting indirect
|
||||
iterators. If the base iterator models a more restrictive concept,
|
||||
the resulting indirect iterators will model the same concept <a
|
||||
href="#3">[3]</a>.
|
||||
|
||||
|
||||
<h3>Members</h3>
|
||||
The resulting <tt>iterator</tt> and <tt>const_iterator</tt> types implement
|
||||
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 they support the following constructors:
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
explicit indirect_iterator_pair_generator::iterator(const BaseIterator& it)
|
||||
explicit indirect_iterator_pair_generator::const_iterator(const BaseIterator& it)
|
||||
</pre>
|
||||
</blockquote>
|
||||
<br>
|
||||
<br>
|
||||
|
||||
<hr>
|
||||
|
||||
<p>
|
||||
|
||||
<h2><a name="make_indirect_iterator">The Indirect Iterator Object
|
||||
Generator</a></h2>
|
||||
The <tt>make_indirect_iterator()</tt> function provides a more convenient
|
||||
way to create indirect iterator objects. The function saves the user the
|
||||
trouble of explicitly writing out the iterator types.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
template <class BaseIterator>
|
||||
typename indirect_iterator_generator<BaseIterator>::type
|
||||
make_indirect_iterator(BaseIterator base)
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
<h3>Example</h3>
|
||||
Here we again print the <tt>char</tt>s from the array <tt>characters</tt>
|
||||
by accessing them through the array of pointers <tt>pointer_to_chars</tt>,
|
||||
but this time we use the <tt>make_indirect_iterator()</tt> function which
|
||||
saves us some typing.
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
// continuing from the last example...
|
||||
|
||||
std::copy(boost::make_indirect_iterator(pointers_to_chars),
|
||||
boost::make_indirect_iterator(pointers_to_chars + N),
|
||||
std::ostream_iterator<char>(std::cout, ","));
|
||||
std::cout << std::endl;
|
||||
|
||||
return 0;
|
||||
}
|
||||
</pre>
|
||||
</blockquote>
|
||||
The output is:
|
||||
|
||||
<blockquote>
|
||||
<pre>
|
||||
a,b,c,d,e,f,g,
|
||||
</pre>
|
||||
</blockquote>
|
||||
<hr>
|
||||
|
||||
<h3>Notes</h3>
|
||||
|
||||
<p>
|
||||
|
||||
<p><a name="2">[2]</a> If your compiler does not support partial
|
||||
specialization and the base iterator or its <tt>value_type</tt> is a
|
||||
builtin pointer type, you will not be able to use the default for
|
||||
<tt>Value</tt> and will need to specify this type explicitly.
|
||||
|
||||
<p><a name="3">[3]</a>There is a caveat to which concept the
|
||||
indirect iterator can model. If the return type of the
|
||||
<tt>operator*</tt> for the base iterator's value type is not a
|
||||
true reference, then strickly speaking, the indirect iterator can
|
||||
not be a model of <a href=
|
||||
"http://www.sgi.com/tech/stl/ForwardIterator.html">Forward
|
||||
Iterator</a> or any of the concepts that refine it. In this case
|
||||
the <tt>Category</tt> for the indirect iterator should be
|
||||
specified as <tt>std::input_iterator_tag</tt>. However, even in
|
||||
this case, if the base iterator is a random access iterator, the
|
||||
resulting indirect iterator will still satisfy most of the
|
||||
requirements for <a href=
|
||||
"http://www.sgi.com/tech/stl/RandomAccessIterator.html">Random
|
||||
Access Iterator</a>.
|
||||
|
||||
<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>© Copyright Jeremy Siek and David Abrahams 2001. 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 BaseIterator const namespace struct
|
||||
-->
|
||||
|
||||
<!-- LocalWords: ConstPointer ConstReference typename iostream int abcdefg
|
||||
-->
|
||||
<!-- LocalWords: sizeof PairGen pre Jeremy Siek David Abrahams
|
||||
-->
|
||||
|
||||
|
||||
</body>
|
||||
</html>
|
||||
Reference in New Issue
Block a user