[Boost-users] Shortest path problem: distance between two vertices

I am kind of new to C++ and also boost library, trying to use the bfs to find the distance between two vertices in a graph. As I read from previous posts, the easiest way would be to throw an exception once the target vertex has been discovered. Now the problem is that I can't figure out how to do this, and this is pretty urgent! Can you help me with a few lines of code which make the bfs_visitor and call the bfs function for this purpose? Thanks a lot!