Hi Andrew, Would you please tell me which part of the documentation I should rely on to use a std::map as you'd suggested? I should actually admit I'm not yet familiar with the BGL :-) -----Message d'origine----- De : boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org]De la part de Andrew Sutton Envoyé : mercredi 25 mars 2009 17:25 À : boost-users@lists.boost.org Objet : Re: [Boost-users] [Graph] Adjacency list scalability with a Dijkstra algorithm Here is the problem: I would have imagined that, in my case, boost::num_vertices(graph) would have returned 6, but it actually returns the higher vertex number + 1, that is... 4243 ! So each of my vector has a size of 4243 * sizeof(tVertex) bytes... Is there a way to handle that? I probably misuse the API, but it would be better if the container would be dimensioned to the actual number of vertices, since I am in a CPU and memory constraint environment... You're confusing the notions of "index" and "descriptor". With the vertex set using vecS, the descriptor of a vertex is the same as its index -- hence the confusion. Therefore, when you call add_edge(4242, 1, ...), the graph thinks you mean the vertex whose descriptor is 4242 and resizes itself accordingly. You have to remember - whatever the examples may indicate - that you should never actually use a literal value and descriptors interchangeably. This isn't documented very well, either. You could use a std::map to associate your own identifiers with vertex descriptors. Andrew Sutton andrew.n.sutton@gmail.com <mailto:andrew.n.sutton@gmail.com>