Re: [Boost-users] BGL: Problem accessing property_map members

25 Jan 2008

      Hi,

Thanks for the reply - I'm just trying to work out how this fits with  
the example given in interior_property_map.cpp (which compiles and  
runs file), where essentially this is done:

enum vertex_first_name_t { vertex_first_name };
namespace boost {
   BOOST_INSTALL_PROPERTY(vertex, first_name);
}

typedef adjacency_list<vecS, vecS, directedS,
       property<vertex_first_name_t, std::string> > MyGraphType;

MyGraphType G(5);

// then for 11 edges:
add_edge(start, end, G);

property_map<MyGraphType, vertex_first_name_t>::type name
       = get(vertex_first_name, G);

boost::put(name, 0, "Jeremy");
boost::put(name, 1, "Rich");
boost::put(name, 2, "Andrew");
boost::put(name, 3, "Jeff");
name[4] = "Kinis";

Of course, the difference here is that in the example names are being  
assigned to Vertices, not Edges - is this why there is a difference in  
the value assignment method?

Regards,
James.

On 25 Jan 2008, at 05:05, Cromwell Enage wrote:
...
--- James Jackson wrote:
...
Hi,
Hello!
...
I am trying to use the BGL to model a simple
directed graph with internal edge properties.
Following the example given in the
documentation[1], I have done the following
(with question-irrelevant padding removed):
-------------------------------
#include <boost/graph/adjacency_list.hpp>
#include <boost/property_map.hpp>
typedef boost::property<boost::edge_weight_t,
double> EdgeProperties;
typedef boost::adjacency_list<boost::vecS,
boost::vecS,
boost::directedS, boost::no_property,
EdgeProperties> NetworkGraph;
typedef std::pair<int, int> Edge;
NetworkGraph g(5);
boost::add_edge(0, 1, g);
boost::add_edge(0, 2, g);
boost::add_edge(1, 3, g);
boost::add_edge(2, 3, g);
boost::add_edge(3, 4, g);
boost::property_map<NetworkGraph,
boost::edge_weight_t>::type weights
= boost::get(boost::edge_weight_t(), g);
weights[0] = 1.0;
weights[1] = 1.0;
weights[2] = 1.0;
weights[3] = 1.0;
weights[4] = 1.0;
-------------------------------
Which all looks fairly kosher.
Sorry, it isn't.
Edge maps require edge_descriptors for keys.  First,
change your Edge type definition to this:
typedef NetworkGraph::edge_descriptor Edge;
Then, for adding edges, do the following:
Edge e;
   bool b;
boost::tie(e, b) = boost::add_edge(0, 1, g);
if (b)
   {
       weights[e] = 1.0;
   }
// etc.
HTH,
                             Cromwell D. Enage
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