Hi to all, I'm studying the BGL, and I've a question. I've noticed that: - the traversing algorithms, like breadth first search, only decide how to traverse the graph, but do not perform specific calculations; - if I want to perform any calculation during the traverse, I can do it passing a custom visitor to the algorithm. But the question is: how can I customize the traverse method? The algorithms always explore enterely the graph. EXAMPLE: every edge (u, v) of a graph have a property "edge_can_traverse_t" that says on which of adjacent edges starting from v I can continue the traverse. _C _F o| /| o / o / A---->B---->D o o o >G \ \ \ \ _\| _\| E H ----------------------------------------- | edge | property edge_can_traverse_t | | | (vector<edge>) | ----------------------------------------- | (A,B) | (B,D) , (B,E) | | (B,C) | empty | | (B,D) | (D,F) , (D,H) | | (B,E) | empty | | (D,F) | empty | | (D,G) | empty | | (D,H) | empty | ----------------------------------------- For example, if I come from the (A,B) edge, I want that the algorithm consider only the (B,D) and (B,E) edge, and skip the (B,C) edge. The solution I found is to modify the breadth_first_search algorithm, adding a predicate to the visitor and performing a control when the algorithm examines the outer edges of the current vertex. Something like this: //============================================================================== // PREDICATE (in the visitor) //============================================================================== template <class IncidenceGraph, class PredecessorMap> bool can_traverse_edge( edge_descriptor e, IncidenceGraph &g, PredecessorMap p ) { typedef graph_traits<IncidenceGraph>::vertex_descriptor VertexDescriptor; VertexDescriptor u = source( e, g ); // select the source of the edge EdgeDescriptor eFrom = edge( p(u), u ); // select the previous visited edge if ( e is contained in the edge_can_traverse_t property of eFrom ) return true; else return false; } //------------------------------------------------------------------------------ //============================================================================== // breadth_first_visit //============================================================================== template <class IncidenceGraph, class Buffer, class BFSVisitor, class ColorMap> void customized_breadth_first_visit (const IncidenceGraph& g, typename graph_traits<IncidenceGraph>::vertex_descriptor s, Buffer& Q, BFSVisitor vis, ColorMap color) { [.....] put(color, s, Color::gray()); vis.discover_vertex(s, g); Q.push(s); while (! Q.empty()) { Vertex u = Q.top(); Q.pop(); vis.examine_vertex(u, g); for (tie(ei, ei_end) = out_edges(u, g); ei != ei_end; ++ei) { if ( !vis.can_traverse_edge( *ei ) ) continue; [.....] } //------------------------------------------------------------------------------ Does it exist a better mechanism to control the traverse with the BGL? Or I must implement my solution? Best Regards, Cosimo Calabrese.