Question

I have a need to use the Boost library to get the shortest path from one point to another. I’ve looked over the example code and it is decently easy to follow. However, the example only shows how to get the overall distances. I’m trying to figure out how to iterate over the predecessor map to actually get the shortest path and I can’t seem to figure it out. I’ve read these two questions on the subject:

Dijkstra Shortest Path with VertexList = ListS in boost graph

Boost:: Dijkstra Shortest Path, how to get vertice index from path iterator?

But in both of the examples provided, the IndexMap typedef doesn’t seem to work with the Visual Studio compiler and, frankly, Boost typedefs are a little confusing to me and I’m having some trouble figuring all of this out. Based on the Boost example code here, could anyone tell me how I can just get the path out of it? I would be very thankful.

http://www.boost.org/doc/libs/1_46_1/libs/graph/example/dijkstra-example.cpp

Answer 1

If you just want to get the path from the predecessor map you can do it like this.

//p[] is the predecessor map obtained through dijkstra
//name[] is a vector with the names of the vertices
//start and goal are vertex descriptors
std::vector< graph_traits< graph_t >::vertex_descriptor > path;
graph_traits< graph_t >::vertex_descriptor current=goal;

while(current!=start) {
    path.push_back(current);
    current=p[current];
}
path.push_back(start);

//This prints the path reversed use reverse_iterator and rbegin/rend
std::vector< graph_traits< graph_t >::vertex_descriptor >::iterator it;
for (it=path.begin(); it != path.end(); ++it) {

    std::cout << name[*it] << " ";
}
std::cout << std::endl;