How to get the type of a property in Boost Graph Library

Question

In Boost Graph Library (BGL), how can I programmatically get the type of a property such as the one associated with boost::edge_weight_t?

I searched and found lots of examples on how to get the type of the property map, but not the type of the property itself. For example, BGL documentation below has the type of the property map for edge_weight_t as property_map<DirectedGraph, edge_weight_t>::type:

typedef ... DirectedGraph;
DirectedGraph digraph(V);
{
  ..
  property_map<DirectedGraph, edge_weight_t>::type
    weight = get(edge_weight, digraph);
}

But how do I get the type of the weight of the edges? (float, int etc.)

How do I declare variables for the edge weights with appropriate type expressions (??? below), so that I can, e.g., read into these weight values from a file/stream.

typedef ... DirectedGraph;
...
??? w;
input_s >> w;

Answer 1

As pointed out in comments by @llonesmiz, for a property map type

typedef property_map<Graph, boost::edge_weight_t>::type WeightMap

the type of the property (weight) value can be retrieved with property_traits as:

typedef typename boost::property_traits<WeightMap>::value_type edge_weight_type;