[Boost-users] [graph] [beginner] How to use the "tie(...) feature" with standard c++ containers?

9 Oct 2011

      Hi

recently i started programming with the boost graph library. You can use
nice syntax for iterating over a set of vertices or edges by writing for
example:

//begin program
#include <iostream>
#include <boost/graph/adjacency_list.hpp>

typedef boost::adjacency_list < boost::listS, boost::vecS,
boost::bidirectionalS> 
my_graph;

typedef boost::graph_traits <my_graph> 
my_graph_traits;

int main()
{
	my_graph g(5);
	my_graph_traits::vertex_iterator vi, vi_end;

	for (boost::tie (vi, vi_end) = vertices (g); vi != vi_end; ++vi)
	{
		std::cout << "vertex: " << *vi << std::endl; 
	}
}
//End program

Outputs:
vertex: 0
vertex: 1
vertex: 2
vertex: 3
vertex: 4

My question is now how to define functions 'tie(...)' and
'elements(...)' for using them with standard containers.

Suppose you have a container like the list:

std::list <unsigned int> list(4);

Now to iterate over all elements i would like to write something like

//begin snippet
std::list <unsigned int>::iterator begin, end;
for (tie (begin, end) = elements (list); begin != end; ++begin)
	;// do some thing
//end snippet

In stead of writing:

//begin snippet
begin = list.begin(); 
end = list.end();

for (; begin != end; ++begin)
	;// do some thing
//end snippet

I started defining the function elements(...) like this:

template <typename T> 
std::pair < typename T::iterator, typename T::iterator>
elements (T container)
{
	return std::make_pair(container.begin(), container.end());
}

The compiler tells me, that 'tie' was not declared in this scope. So i
assume that i also have to define the 'tie' function in some way. Maybe
there is already some functionality to access the standard containers
the way you can do it with 'tie' or maybe you could give me some hint to
solve the problem.

best regards
Christoph