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? ----------------------------------------------------------------------- //Here is the simpilfied situation that I want to handle, "IF THERE IS NOT a vertex representing the //string of the current line" is the predicate I want to know typedef adjacency_list<vecS, vecS, directedS, property<vertex_color_t, default_color_type>, property<edge_weight_t, int> > Graph; Graph g(); ifstream infile; infile.open(argv[1]); string line; while( getline(infile, line) ){ if(line.find("Node")!= npos && /*IF THERE IS NOT a vertex representing the string of the current line*/) add_vertex( line, g); } -------------------------------------------------------------------- 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. Thanks a lot, Sean _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today - it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/