Output BGL Edge Weights

Question

I am trying to iterate through the edges of a graph and output their edge weights. I am confused though. I know how to output the "edges", but this is actually just a (vertex, vertex) which defines the edge. So do I index *edgePair.first into the EdgeWeightMap to get the weight of the edge starting from vertex *edgePair.first? This doesn't compile : "no match for operator<<".

#include <iostream>
#include <boost/graph/graph_traits.hpp>
#include <boost/graph/adjacency_list.hpp>

typedef boost::property<boost::edge_weight_t, double> EdgeWeightProperty;
typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, EdgeWeightProperty> Graph;

int main(int,char*[])
{
  // Create a graph object
  Graph g(2);

  EdgeWeightProperty e = 5;
  add_edge(0, 1, e, g);

  boost::property_map<Graph, boost::edge_weight_t>::type EdgeWeightMap = get(boost::edge_weight_t(), g);

  typedef boost::graph_traits<Graph>::edge_iterator edge_iter;
  std::pair<edge_iter, edge_iter> edgePair;
  for(edgePair = edges(g); edgePair.first != edgePair.second; ++edgePair.first)
  {
      std::cout << EdgeWeightMap[*edgePair.first] << " ";
  }

  return 0;
}

Any thoughts?

Thanks, David

Answer 1

In this code, EdgeWeightProperty is declared as a vertex property rather than an edge property, and so it doesn't make sense to insert edges with that property. Try adding boost::no_property before EdgeWeightProperty in your adjacency_list typedef. Also, you might want to use get(EdgeWeightMap, *edgePair.first) rather than operator[] because that will work with more property map types.