Re: [Boost-users] Boost Graph: edge indices

Hi! The edge_index internal property map is not created by default, so you have to define it explicitly: typedef adjacency_list > MyGraph; typedef property_map::type MyEdgeIndexMap; ... // Retrieve the edge index map associated with the graph MyEdgeIndexMap emap = get(edge_index, g); ... // Convert the edge descriptor to an integer value cout << index[ get(emap, e, g) ] << endl; The vertex descriptor is an integer value so it works with operator[], but edge descriptor is an std::pair<>, so you have to convert it to an integer with the appropriate edge index map. This leaves only one question: how do you use bundled edge properties along with edge index map? Cheers, Gabe On Thu, Apr 1, 2010 at 3:19 AM, Trevor Harmon wrote:

Hi,

In the Boost Graph library, vertices have an index (vertex_index_t), and I was under the impression that edges have one, too. At least, there's a predefined type called edge_index_t. However, I can't figure out how to access an edge's index. For example, consider a graph defined like:

typedef adjacency_list MyGraph; typedef graph_traits<MyGraph>::vertex_descriptor Vertex; typedef graph_traits<MyGraph>::edge_descriptor Edge;

And let's say I've got a vertex descriptor called "u". I can iterate over u's outgoing edges like this:

typedef graph_traits<MyGraph>::out_edge_iterator out_iter; std::pair outp; for (outp = out_edges(u, g); outp.first != outp.second; ++outp.first) {    Edge e = *outp.first;    Vertex v = target(e, g);    cout << index[v] << std::endl;  // Works fine    cout << index[e] << std::endl;  // Compiler error }

In this example, index[v] works as expected, but index[e] gives me a compiler error: "no match for ‘operator[]’ in ‘index[e]".

Perhaps my graph typedef needs to be changed so that its edges have a property map for edge_index_t, although I'm not sure how to do that. (And anyway I wouldn't expect vertices to have indices by default but edges not...)

Thanks for any help,

Trevor

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