On Fri, 1 Apr 2011, Cedric Laczny wrote:
Hi,
I have modified the astar-cities.cpp example to use an external rank_map based on iterator_property_map. The following should give you an idea:
vector<cost> v_vec(num_vertices(g), 0.0);
typedef property_map< mygraph_t, vertex_index_t>::type VertexIndexMap; VertexIndexMap v_index = get(vertex_index, g); // Initialization of interest // Create the external property map typedef iterator_property_map< std::vector< cost >::iterator, VertexIndexMap
CostMap; CostMap c_map(v_vec.begin(), v_index);
and the function-call of astar_search is as follows:
astar_search (g, start, distance_heuristic
(locations, goal, name), predecessor_map(&p[0]).distance_map(&d[0]). visitor(a_star_vis). rank_map(c_map)); // Here we use the "global" cost map Basically, the code is the same as in the example, with only the addition of the explicit rank_map.
Now I am fairly confused that the function call seems to behave the same if I have "get(vertex_index, g)" and if I don't have it. This comes unexpected to me as I would think that it needs OffsetMap (v_index) to correctly find the index in the random access container (v_vec). But when I simply declare an object it is not yet initialized and will not contain any meaningfull offsets (not using "get(vertex_index, g)"). So why does it work, when the map is not initialized? Or what am I missing here please?
The default index map is just a typed_identity_property_map, and that class doen't have any parameters to its constructor. However, you should not rely on those properties, since algorithms in BGL have broken because their authors assumed the vertex index map was the identity then users passed in graphs (such as adjacency_list with listS as the vertex container) with non-identity maps. -- Jeremiah Willcock