Re: [Boost-users] Problem using edge_descriptors as indices into an external property

Hi Andrea, On Jun 13, 2005, at 7:07 AM, Andrea Olgiati wrote:

I've encountered a problem whilst compiling the following program, and I can't quite figure out why it shouldn't work. Whilst compiling usign boost 1.32.0 and gcc 3.3.4, I get cannot convert `boost::detail::edge_desc_impl' to `int'    for argument `2' to `const T& get(const T*, int) [with T = int]'

I believe this is saying that edge descriptors cannot be used as indices into a property map (that is, "wm"). Why is this different from vertex descriptors, which are accepted as indices into "p" and "dist"?

The problem here is that std::vectors really only work as property maps when the descriptors are integers and, unfortunately, that only works with vertex descriptors (in some limited cases). The easiest way to solve the problem is to make "wm" an internal property map, by putting the edge weight into the graph itself. There's an updated version of your code below, where I've done three things: (1) I added an "edge_weight" property to each edge, by changing the Graph typedef. (2) I changed the definition of "wm" so that it is a property map accessing the weights of each edge (that are stored inside the graph itself). (3) The call to bellman_ford_shortest_paths just passes the property map "wm", instead of &wm[0]. Doug #include #include #include int main () { typedef boost::adjacency_list > Graph; Graph G; boost::property_map::type wm = boost::get(boost::edge_weight, G); std::vector < boost::graph_traits < Graph >::vertex_descriptor > p; std::vector < int > dist; boost::bellman_ford_shortest_paths (G, boost::num_vertices(G), wm, &p[0], &dist[0], boost::closed_plus < int >(), std::less < int >(), boost::default_bellman_visitor ()); return 0; }