Hi Andrew, Thank you very much for your reply. I eventually implemented Steven Watanabe's solution, which seems easier to me. Since I only need to know which nodes are actually reachable, I may get rid of distances for now. Thanks again, Florian -----Message d'origine----- De : boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org]De la part de Andrew Sutton Envoyé : vendredi 20 mars 2009 18:35 À : boost-users@lists.boost.org Objet : Re: [Boost-users] [Graph] Computing reachable vertices on a graph However, I encounter the following issue : in this example, vertices are numbered from 0 to 5. However, in my project, this is not the case, vertices could be numbered 5, 38, 42, 384... Using a vector in that case might not work as expected, a map would probably be better. I'm not quite familiar with BGL so far, maybe should I deal with a specific property map? Or using a visitor to record a vertex distance upon graph discovery? I'm a little bit lost, any help will be greatly appreciated! You probably shouldn't rely on vertex indices as the canonical id of the vertex. The method of identifying vertices (and edges) in an adjacency list varies with the vertex set and edge set type selectors (indices or identifeirs for vecS aren't the same as listS). There are a couple of different approaches. The easiest would be to simply maintain a mapping of id to vertex descriptor. For example: map verts; verts[5] = add_vertex(g); verts[58] = add_vertex(g); // and so on. You can couple that bundled vertex properties to get a kind of bimap. struct vertex_props { int id; } typedef adj_list Graph; template void add_vertex(Graph& g, Map& verts, int id) { vertex_descriptor v = add_vertex(g); verts[id] = v; g[v].id = id; } add_vertex(g, verts, 5); add_vertex(g, verts, 58); ... cout << g[*vertices(g).begin]->id << "\n"; Hope that helps, Andrew Sutton andrew.n.sutton@gmail.com mailto:andrew.n.sutton@gmail.com