Is it safe to store vertex descriptors? Does adding a new vertex / edge
ever renumber existing vertices? (I know removing does this)
Say I have a class to represent a state from the USA.
class State { ... };
and I have a bunch of instances:
State california, oregon, nevada, hawaii, ...;
I want a graph with a vertex for each state and an edge for each border:
typedef adjacency_list Graph;
Graph graph;
I build my graph like this:
Graph::vertex_descriptor v_california = add_vertex(graph);
Graph::vertex_descriptor v_oregon = add_vertex(graph);
Graph::vertex_descriptor v_nevada = add_vertex(graph);
Graph::vertex_descriptor v_hawaii = add_vertex(graph);
...
add_edge(v_california, v_oregon, graph);
add_edge(v_california, v_nevada, graph);
add_edge(v_nevada, v_oregon, graph);
...
To associate each State instance with a vertex, I make a map:
map state_to_vtx_map;
state_to_vtx_map[california] = v_california;
state_to_vtx_map[oregon ] = v_oregon ;
state_to_vtx_map[nevada ] = v_nevada ;
state_to_vtx_map[hawaii ] = v_hawaii ;
Now I can find all the states Nevada has a border with by doing this:
Graph::vertex_descriptor v = state_to_vtx_map[nevada];
tie(begin, end) = out_edges(v, g);
(please assume that I didn't store v_nevada from above)
Is my state_to_vtx_map safe? Since a delete can totally renumber
everything, I don't think it is safe. What's the correct way of
associating a vertex with a State instance?
Thanks,
Cory
