[Boost-users] property map: does a given key exist?

From: Irek Szczesniak (ijs_at_[hidden])
Date: 2006-04-15 16:25:23

In nutshell: how can I check whether a property map has some given
key?

The exact problem is as follows.  I have graph edges with the property
"lambdas" of positive integers, but its the exact meaning is not
important here.  With the read_graphviz function I am loading graph
files which look like this:

graph {
   a;
   b;
   c;
   c -- a [distance="100"];
   a -- b [lambdas="8"];
}

After I load the file I want to examine which edges have the "lambdas"
property, but I don't know how to do this.  If I request the property
value with the "get" function, I get some random value.  My program is
at the bottom of this email.

The program prints the edge and the value of the "lambdas" property.
I get this:

(2,0): 33489268
(0,1): 8

The first line is bad: the edge (2,0), i.e. c -- a in my graphviz
file, has the reported value of 33489268.  The second line is OK.

Thanks for reading.

Best,
Irek

*********************************************************************

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/depth_first_search.hpp>
#include <boost/graph/iteration_macros.hpp>
#include <boost/graph/graphviz.hpp>

using namespace boost;

typedef boost::adjacency_list<vecS, vecS, undirectedS,
        property<vertex_name_t, std::string>,
        property<edge_weight_t, double,
                property<edge_weight2_t, int> >,
        no_property > Graph;

int
main()
{
   Graph g;
   dynamic_properties dp;

   dp.property("node_id", get(vertex_name, g));
   dp.property("distance", get(edge_weight, g));
   dp.property("lambdas", get(edge_weight2, g));

   read_graphviz(std::cin, g, dp);

   typedef boost::property_map<Graph, edge_weight2_t>::type lambdas_t;

   lambdas_t weight2_map = get(edge_weight2, g);

   BGL_FORALL_EDGES(e, g, Graph)
     // Before printing this out I would like to make sure that an edge
     // has this property.
     std::cout << e << ": " << get(weight2_map, e) << std::endl;
}