[Boost-users] How to test whether a vertex or edge exists?

From: sean yang (seanatpurdue_at_[hidden])
Date: 2006-05-06 23:49:43

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

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