[boost] Re: How to get an unique identifier for an edge

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-04-06 06:03:25

Hi Lodewijk,

> I tried to get an unique identifier for a node and an
> edge. The node is possible e.g.:

> However, the same idee does not work for an edge:
> 
> std::pair<adjacency_list<>::edge_iterator,adjacency_list<>::edge_iterator>
> pe;
>   property_map< adjacency_list<> , edge_index_t>::type
> inedge;
>   inedge = get(edge_index_t(), processGraph);
>   for (pe = edges(someGraph); pe.first != pe.second;
> ++pe.first) {
>     cout << *pe.first << "   ";
>     cout << "index: " << inedge[*pe.first] << "  \n";
>   }
> 
> I can not figure out how to get an unique id for an
> edge and I can not understand how the property maps
> works from the documentation nor I can find how such a
> edge_index_t property is defined. Can somebody provide
> some help.

The reason is that vertex_index_t property is automatically defined for
adjacency_list<>. It's not the case for edge_vertex_t. You'd have to:

   adjacency_list<vecS, vecS, directedS, no_property, 
        property<edge_index_t, unsigned> > g;

   unsigned index(0);
   ...edge_iterator i, e;
   for(tie(i, e) = edges(i, e); i != e; ++i, ++index)
        put(edge_index, process_graph, *i, index);

In other words, you have initialize and maintain edge_index property
yourself.

HTH,
Volodya