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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>Shared Container Iterator Documentation</title>
</head>
<body bgcolor="#FFFFFF" text="#000000">
<img src="../../boost.png" alt="boost.png (6897 bytes)"
align="center" width="277" height="86">
<h1>Shared Container Iterator</h1>
Defined in header
<a href="../../boost/shared_container_iterator.hpp">boost/shared_container_iterator.hpp</a>
<p>
The purpose of the shared container iterator is to attach the lifetime
of a container to the lifetime of its iterators. In other words, the
container will not be deleted until after all its iterators are
destroyed. The shared container iterator is typically used to
implement functions that return iterators over a range of objects that
only need to exist for the lifetime of the iterators. By returning a
pair of shared iterators from a function, the callee can return a
heap-allocated range of objects whose lifetime is automatically managed.
<p>
The shared container iterator augments an iterator over a shared
container. It maintains a reference count on the shared
container. If only shared container iterators hold references to
the container, the container's lifetime will end when the last shared
container iterator over it is destroyed. In any case, the shared
container is guaranteed to persist beyond the lifetime of all
the iterators. In all other ways, the
shared container iterator behaves the same as its base iterator.
<h2>Synopsis</h2>
<pre>
namespace boost {
template <typename <a href="http://www.sgi.com/tech/stl/Container.html">Container</a>>
class shared_container_iterator;
template <typename <a href="http://www.sgi.com/tech/stl/Container.html">Container</a>>
shared_container_iterator<Container>
make_shared_container_iterator(typename Container::iterator base,
boost::shared_ptr<Container> const& container);
std::pair<
typename shared_container_iterator<Container>,
typename shared_container_iterator<Container>
>
make_shared_container_range(boost::shared_ptr<Container> const& container);
}
</pre>
<hr>
<h2><a name="generator">The Shared Container Iterator Type</a></h2>
<pre>
template <typename Container> class shared_container_iterator;
</pre>
The class template <tt>shared_container_iterator</tt>
is the shared container iterator type. The <tt>Container</tt> template
type argument must model the
<a href="http://www.sgi.com/tech/stl/Container.html">Container</a>
concept.
<h3>Example</h3>
<p>
The following example illustrates how to create an iterator that
regulates the lifetime of a reference counted <tt>std::vector</tt>.
Though the original shared pointer <tt>ints</tt> ceases to exist
after <tt>set_range()</tt> returns, the
<tt>shared_counter_iterator</tt> objects maintain references to the
underlying vector and thereby extend the container's lifetime.
<p>
<a href="./shared_iterator_example1.cpp">shared_iterator_example1.cpp</a>:
<PRE>
<font color="#008040">#include "shared_container_iterator.hpp"</font>
<font color="#008040">#include "boost/shared_ptr.hpp"</font>
<font color="#008040">#include <algorithm></font>
<font color="#008040">#include <iostream></font>
<font color="#008040">#include <vector></font>
<B>typedef</B> boost::shared_container_iterator< std::vector<<B>int</B>> > iterator;
<B>void</B> set_range(iterator& i, iterator& end) {
boost::shared_ptr< std::vector<<B>int</B>> > ints(<B>new</B> std::vector<<B>int</B>>());
ints->push_back(<font color="#0000A0">0</font>);
ints->push_back(<font color="#0000A0">1</font>);
ints->push_back(<font color="#0000A0">2</font>);
ints->push_back(<font color="#0000A0">3</font>);
ints->push_back(<font color="#0000A0">4</font>);
ints->push_back(<font color="#0000A0">5</font>);
i = iterator(ints->begin(),ints);
end = iterator(ints->end(),ints);
}
<B>int</B> main() {
iterator i,end;
set_range(i,end);
std::copy(i,end,std::ostream_iterator<<B>int</B>>(std::cout,<font color="#0000FF">","</font>));
std::cout.put(<font color="#0000FF">'\n'</font>);
<B>return</B> <font color="#0000A0">0</font>;
}
</PRE>
The output from this part is:
<pre>
0,1,2,3,4,5,
</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/Container.html"><tt>Container</tt></a></TD>
<TD>The type of the container that we wish to iterate over. It must be
a model of the
<a href="http://www.sgi.com/tech/stl/Container.html"><tt>Container</tt></a>
concept.
</TD>
</TR>
</Table>
<h3>Model of</h3>
The <tt>shared_container_iterator<Container></tt> type models the
same iterator concept as the base iterator
(<tt>Container::iterator</tt>).
<h3>Members</h3>
The shared container 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, though only operations defined for the base iterator will be valid.
In addition it has the following constructor:
<pre>
shared_container_iterator(Container::iterator const& it,
boost::shared_ptr<Container> const& container)
</pre>
<p>
<hr>
<p>
<h2><a name="make_iterator">The Shared Container Iterator Object Generator</a></h2>
<pre>
template <typename Container>
shared_container_iterator<Container>
make_shared_container_iterator(Container::iterator base,
boost::shared_ptr<Container> const& container)
</pre>
This function provides an alternative to directly constructing a
shared container iterator. Using the object generator, a shared
container iterator can be created and passed to a function without
explicitly specifying its type.
<h3>Example</h3>
This example, similar to the previous, uses
<tt>make_shared_container_iterator()</tt> to create the iterators.
<p>
<a href="./shared_iterator_example2.cpp">shared_iterator_example2.cpp</a>:
<PRE>
<font color="#008040">#include "shared_container_iterator.hpp"</font>
<font color="#008040">#include "boost/shared_ptr.hpp"</font>
<font color="#008040">#include <algorithm></font>
<font color="#008040">#include <iterator></font>
<font color="#008040">#include <iostream></font>
<font color="#008040">#include <vector></font>
<B>template</B> <<B>typename</B> Iterator>
<B>void</B> print_range_nl (Iterator begin, Iterator end) {
<B>typedef</B> <B>typename</B> std::iterator_traits<Iterator>::value_type val;
std::copy(begin,end,std::ostream_iterator<val>(std::cout,<font color="#0000FF">","</font>));
std::cout.put(<font color="#0000FF">'\n'</font>);
}
<B>int</B> main() {
<B>typedef</B> boost::shared_ptr< std::vector<<B>int</B>> > ints_t;
{
ints_t ints(<B>new</B> std::vector<<B>int</B>>());
ints->push_back(<font color="#0000A0">0</font>);
ints->push_back(<font color="#0000A0">1</font>);
ints->push_back(<font color="#0000A0">2</font>);
ints->push_back(<font color="#0000A0">3</font>);
ints->push_back(<font color="#0000A0">4</font>);
ints->push_back(<font color="#0000A0">5</font>);
print_range_nl(boost::make_shared_container_iterator(ints->begin(),ints),
boost::make_shared_container_iterator(ints->end(),ints));
}
<B>return</B> <font color="#0000A0">0</font>;
}
</PRE>
Observe that the <tt>shared_container_iterator</tt> type is never
explicitly named. The output from this example is the same as the previous.
<h2><a name="make_range">The Shared Container Iterator Range Generator</a></h2>
<pre>
template <typename Container>
std::pair<
shared_container_iterator<Container>,
shared_container_iterator<Container>
>
make_shared_container_range(boost::shared_ptr<Container> const& container);
</pre>
Class <tt>shared_container_iterator</tt> is meant primarily to return,
using iterators, a range of values that we can guarantee will be alive as
long as the iterators are. This is a convenience
function to do just that. It is equivalent to
<pre>
std::make_pair(make_shared_container_iterator(container->begin(),container),
make_shared_container_iterator(container->end(),container));
</pre>
<h3>Example</h3>
In the following example, a range of values is returned as a pair of
<tt>shared_container_iterator</tt> objects.
<p>
<a href="./shared_iterator_example3.cpp">shared_iterator_example3.cpp</a>:
<PRE>
<font color="#008040">#include "shared_container_iterator.hpp"</font>
<font color="#008040">#include "boost/shared_ptr.hpp"</font>
<font color="#008040">#include "boost/tuple/tuple.hpp" // for boost::tie</font>
<font color="#008040">#include <algorithm> // for std::copy</font>
<font color="#008040">#include <iostream> </font>
<font color="#008040">#include <vector></font>
<B>typedef</B> boost::shared_container_iterator< std::vector<<B>int</B>> > iterator;
std::pair<iterator,iterator>
return_range() {
boost::shared_ptr< std::vector<<B>int</B>> > range(<B>new</B> std::vector<<B>int</B>>());
range->push_back(<font color="#0000A0">0</font>);
range->push_back(<font color="#0000A0">1</font>);
range->push_back(<font color="#0000A0">2</font>);
range->push_back(<font color="#0000A0">3</font>);
range->push_back(<font color="#0000A0">4</font>);
range->push_back(<font color="#0000A0">5</font>);
<B>return</B> boost::make_shared_container_range(range);
}
<B>int</B> main() {
iterator i,end;
boost::tie(i,end) = return_range();
std::copy(i,end,std::ostream_iterator<<B>int</B>>(std::cout,<font color="#0000FF">","</font>));
std::cout.put(<font color="#0000FF">'\n'</font>);
<B>return</B> <font color="#0000A0">0</font>;
}
</PRE>
Though the <tt>range</tt> object only lives for the duration of the
<tt>return_range</tt> call, the reference counted
<tt>std::vector</tt> will live until <tt>i</tt> and <tt>end</tt>
are both destroyed. The output from this example is the same as
the previous two.
<hr>
<!-- hhmts start -->
Last modified: Mon Aug 11 11:27:03 EST 2003
<!-- hhmts end -->
<p>© Copyright 2003 The Trustees of Indiana University.
Use, modification and distribution is subject to the Boost Software
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
http://www.boost.org/LICENSE_1_0.txt)</p>
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