On Saturday 06 May 2006 22:49, sean yang wrote:
I want to add a vertex, which a string as its ID to a graph if a vertex representing such a string does not exist in the graph. Is there a function call to test if a vertex exists in a graph?
I don't think there's any particularly efficient way of doing that. Could you first read the strings into a set and then create vertices based on what's in the set? There isn't a function to test if a vertex is in a graph because it isn't needed. The only way to get a vertex is to dereference a vertex_iterator, and obviously such a vertex *is* in the graph. Except for default construction, there isn't even a general way to construct a vertex. How could there be? Vertex descriptors are required to be default constructible, assignable, and equality comparable, but beyond that their representation is arbitrary, so there's no way for a generic algorithm to create one. Having said that, it is possible for any particular graph class to provide a method for creating valid vertices, and adjacency_list provides the function vertex( n, g ), which returns the nth vertex in g. I haven't read the source for this function, but I assume that if n is out of range it does something reasonable like return graph_traits<adjacency_list>::null_vertex().
A related question I want to ask is whether there exist a function call that test whether an edge representing [vertext string("Node1") --> vertext string("Node2") ] exists in a graph.
There's a function edge( u, v, g ) returns the edge between u and v, if it exists. This function is required by the AdjacencyMatrix concept. D.