BGL properties question

From: Jeff Holle (jeff.holle_at_[hidden])
Date: 2003-03-27 15:58:17

I would like to write a "generic" routine that prints the named vertex 
and edges properties.

I can see in this code sibit (from graphviz.cpp) that the info that I 
want is present:

> vertex_label(const Vertex& u, const GraphvizDigraph& g) {
>   boost::property_map<GraphvizDigraph, 
> boost::vertex_attribute_t>::const_type
>     va = boost::get(boost::vertex_attribute, g);
>   return (*(va[u].find("label"))).second;
> }

It appears that va is a map<Vertex, map<string, "property value"> >

How would I write code that prints the names of the properites of a 
given vertex?  (It would involve iterating over the map whose find 
method is used in the above code segment).