Hi, Assuming that I want a graph made of 6 nodes, numbered 1, 2, 3, 4, 5 and 4242. I build the graph this way: typedef boost::adjacency_list<boost::listS, boost::vecS, boost::directedS, boost::no_property, boost::property<boost::edge_weight_t, int> > tGraphShortestpath; tGraphShortestpath graph; boost::add_edge(1, 2, 1234); // 1234 is the weight boost::add_edge(1, 3, 412); ... boost::add_edge(5, 2, 29); boost::add_edge(5, 4242, 84); boost::add_edge(4242, 2, 456); boost::add_edge(4242, 5, 680); Now, I want to apply the Dijkstra algorithm on this graph. I create a distance and a predecessor vector, as I have seen on the documentation online : typedef tGraphShortestpath::vertex_descriptor tVertex; std::vector<tVertex> predecessors(boost::num_vertices(graph)); std::vector<int> distances(boost::num_vertices(graph)); 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... Thank you very much for your help! -- Florian PONROY Thales Land & Joint France Tel. : +33(0)1 41 304 363 Fax : +33(0)1 41 303 560 Email : florian.ponroy@fr.thalesgroup.com