Hi, I ran into trouble after changing my directed adjacency_list into an undirected graph. The following code causes a segfault: for (set<Node>::iterator n = nodes.begin(); n != nodes.end(); ++n) { graph_traits<Graph>::out_edge_iterator edges_begin, edges_end; tie(edges_begin, edges_end) = out_edges(*n, g); for (graph_traits<Graph>::out_edge_iterator ne = edges_begin; ne != edges_end; ++ne) { Node nn1 = target(*ne, g); // ... K_o = out_degree(nn1, g); graph_traits<Graph>::out_edge_iterator nn1edges_begin, nn1edges_end; tie(nn1edges_begin, nn1edges_end) = out_edges(nn1, g); int k; graph_traits<Graph>::out_edge_iterator nn1e; for (nn1e = nn1edges_begin; nn1e != nn1edges_end; ++nn1e) { k = 0; if (nodes.count(target(*nn1e, g))) // !!! k++; } } } I cut out most of the stuff not directly related to accessing the graph. It segfaults in the line marked by !!!, so it would seem that out_edges returns an invalid range (I did some debugging and the this line executes quite a few times before the iterator becomes invalid. I can't seem to force gdb to recognise nn1e as a symbol so I can't tell which edge/node is causing the problem. All this is ran after the graph is initialised (it's quite large, ab. 22k nodes and 900k edges). Best regards, Greg