Hello, I have a problem with the example for Prim's minimum spanning tree that can be found here: http://www.boost.org/libs/graph/example/prim-example.cpp The problem is that when compiled in 32 bits but run on a 64 bits computer, and modified with different edges and weights, it does not work anymore. The modified version that exhibits this behaviour is here: http://www.iro.umontreal.ca/~delallea/tmp/prim-example-fail.cpp It is a simplified version (I removed some compiler-specific code for MSVC) where I replaced the edges and weights by a real-life example I have to solve. Here is the output on a 64 bits computer: -> g++ prim-example-fail.cpp -> ./a.out parent[0] = no parent parent[1] = 9 parent[2] = 19 parent[3] = 4 parent[4] = 0 parent[5] = 26 parent[6] = 27 parent[7] = 4 parent[8] = 0 parent[9] = 3 parent[10] = 0 parent[11] = 0 parent[12] = 6 parent[13] = 12 parent[14] = 17 parent[15] = 28 parent[16] = 4 parent[17] = 15 parent[18] = 1 parent[19] = 24 parent[20] = 12 parent[21] = 10 parent[22] = 5 parent[23] = 1 parent[24] = 22 parent[25] = 0 parent[26] = 4 parent[27] = 7 parent[28] = 13 parent[29] = 4 And when compiled in 32 bits with the -m32 option of g++: -> g++ -m32 prim-example-fail.cpp -> ./a.out parent[0] = no parent parent[1] = no parent parent[2] = no parent parent[3] = no parent parent[4] = no parent parent[5] = no parent parent[6] = no parent parent[7] = no parent parent[8] = no parent parent[9] = no parent parent[10] = no parent parent[11] = no parent parent[12] = no parent parent[13] = no parent parent[14] = no parent parent[15] = no parent parent[16] = no parent parent[17] = no parent parent[18] = no parent parent[19] = no parent parent[20] = no parent parent[21] = no parent parent[22] = no parent parent[23] = no parent parent[24] = no parent parent[25] = no parent parent[26] = no parent parent[27] = no parent parent[28] = no parent parent[29] = no parent I don't know if the problems comes from a faulty example or from the Boost Prim's spanning tree algorithm. Unfortunately I find the graph library quite difficult to understand and this example is the only basis I have to work from. Thanks for any help, Olivier