Hi, since a day I was fighting with a strange bug in my program. Finally, I think, I could trace down this error to a problem in the Boost graph library. The following test program crashes, in a call to boost::clear_vertex. #include <cstdlib> #include <boost/tuple/tuple.hpp> #include <boost/graph/adjacency_list.hpp> typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS> graph_t; typedef boost::graph_traits<graph_t>::vertex_descriptor vertex_descriptor; typedef boost::graph_traits<graph_t>::vertex_iterator vertex_iterator; int main() { graph_t G(8); vertex_iterator vi, vi_end, ui, ui_end; for (boost::tie(vi, vi_end)=boost::vertices(G); vi!=vi_end; ++vi) for (boost::tie(ui, ui_end)=boost::vertices(G); ui!=ui_end; ++ui) // if (*vi!=*ui) boost::add_edge(*vi, *ui, G); for (boost::tie(vi, vi_end)=boost::vertices(G); vi!=vi_end; ++vi) boost::clear_vertex(*vi, G); return EXIT_SUCCESS; } It seams to me, there is a double free error, that occurs if the adjacency_list has self-loops. If the if-statement is not commented out, the program does not crash. I am using Boost 1.33.1. Heiko -- -- Perfection is attained not when there is nothing more to add, but -- when there is nothing more to remove. (Antoine de Saint-Exupéry) -- Cluster Computing @ http://www.clustercomputing.de -- Heiko Bauke @ http://www.physics.ox.ac.uk/users/bauke