[Boost-users] [graph] std::priority_queue of vertex_descriptors with extended comparison object will not initialize

27 Oct 2011

      Hi List,

as the Subject states. I would like to initialize a std::priority_queue
with vertex_descriptors and a comparison object as a template parameter
but the compiler tells me:

...
/usr/include/c++/4.5/bits/stl_heap.h:303:4: error: invalid conversion
from ‘unsigned int’ to ‘void*’
/usr/include/c++/4.5/bits/stl_heap.h:303:4: error:   initializing
argument 1 of ‘bool degree_compare::operator()(void* const&, void*
const&)’
...

if i try to initialize the queue and i just don't know why 'bool
degree_compare::operator()(void* const&, void* const&)' comes up.

Could you please help me to initialize my priority_queue?

best regards
Christoph

// begin code

#include <iostream>
#include <map>
#include <queue>
#include <boost/graph/adjacency_list.hpp>
#include <boost/smart_ptr.hpp>

typedef boost::adjacency_list_traits<boost::listS, boost::vecS,
boost::bidirectionalS>
link_adjacency_list_traits;

struct vertex_properties;
struct edge_properties;
struct graph_properties;

struct vertex_properties {
         std::map <int, link_adjacency_list_traits::edge_descriptor >
used_colors;
         // this one works fine, i can use a traits::edge_descriptor
};

struct edge_properties {
         int color;
};

struct degree_compare;
typedef std::priority_queue <
	link_adjacency_list_traits::vertex_descriptor,
	std::vector <link_adjacency_list_traits::vertex_descriptor>,
	degree_compare> VERTEX_DEGREE_PQ;

struct graph_properties {
	int delta;
	boost::shared_ptr <VERTEX_DEGREE_PQ> pq;
};

typedef boost::adjacency_list < boost::listS,
                         boost::listS,
                         boost::bidirectionalS,
                         vertex_properties,
                         edge_properties,
                         graph_properties>
link_graph;

class degree_compare {
	private:
		link_graph g;
	public:
		degree_compare(const link_graph &g): g(g) {std::cout << "Num Vertices:
" << num_vertices(g) << std::endl;}
		bool operator()(const
boost::graph_traits<link_graph>::vertex_descriptor &a,
		const boost::graph_traits<link_graph>::vertex_descriptor &b) {
			return out_degree(a, g) < out_degree(b, g);
		} 
};

int main ()
{
	link_graph g;
	boost::graph_traits<link_graph>::vertex_descriptor a = add_vertex (g);
        degree_compare dc(g);	// init the comparison object

	VERTEX_DEGREE_PQ pq(dc);// init the p_queue with comparison 
				// object fails
        //pq.push(a);
        //pq.top();
}

// end code