Question

I am trying to create a graph of objects which I need to traverse using some traversal algorithm. At this very moment I am stuck trying to create the graph using my custom objects. The way I am trying to accomplish it is as follows:

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/depth_first_search.hpp>
#include <iostream>

using namespace std;
typedef boost::adjacency_list<boost::vecS,boost::vecS,boost::directedS> CustomGraph;
typedef boost::graph_traits<CustomGraph>::vertex_descriptor CustomVertex;

class CustomVisitor:public boost::default_dfs_visitor
{
        public:
                void discover_vertex(CustomVertex v,const CustomGraph& taskGraph) const
                {
                        cerr<<v<<endl;
                        return;
                }


};

class CustomObject{
        private:
                int currentId;
        public:
                CustomObject(int id){
                        currentId = id;
                }

};


int main()
{
        CustomGraph customGraph;
        CustomObject* obj0 = new CustomObject(0);
        CustomObject* obj1 = new CustomObject(1);
        CustomObject* obj2 = new CustomObject(2);
        CustomObject* obj3 = new CustomObject(3);

        typedef std::pair<CustomObject*,CustomObject*> Edge;
        std::vector<Edge> edgeVec;
        edgeVec.push_back(Edge(obj0,obj1));
        edgeVec.push_back(Edge(obj0,obj2));
        edgeVec.push_back(Edge(obj1,obj2));
        edgeVec.push_back(Edge(obj1,obj3));
        customGraph(edgeVec.begin(),edgeVec.end());
        CustomVisitor vis;
        boost::depth_first_search(customGraph,boost::visitor(vis));

        return 0;
}

But this doesn’t seem to be the right way to create objects within the vertices. Can somebody guide me as to what is the correct way to create nodes such that I can retrieve my objects while traversing the graph.

Thanks

Answer 1

Hi I know this is a rather old question, but there might others that can benefit from an answer.

It seems as if you have forgotten to define that your Graph will have a custom class as vertices. You have to add a fourth parameter to your typedef and add a typedef for your edge:

typedef boost::adjacency_list<boost::vecS,boost::vecS,boost::directedS, CustomObject> CustomGraph;
typedef boost::graph_traits<CustomGraph>::vertex_descriptor CustomVertex;
typedef boost::graph_traits<CustomGraph>::edge_descriptor CustomEdge;

Then I usually add my nodes before connecting them with edges:

// Create graph and custom obj's
CustomGraph customGraph
CustomObject obj0(0);
CustomObject obj1(1);
CustomObject obj2(2);
CustomObject obj3(3);

// Add custom obj's to the graph 
// (Creating boost vertices)
CustomVertex v0 = boost::add_vertex(obj0, customGraph);
CustomVertex v1 = boost::add_vertex(obj1, customGraph);
CustomVertex v2 = boost::add_vertex(obj2, customGraph);
CustomVertex v3 = boost::add_vertex(obj3, customGraph);

// Add edge
CustomEdge edge; 
bool edgeExists;
// check if edge allready exist (only if you don't want parallel edges)
boost::tie(edge, edgeExists) = boost::edge(v0 , v1, customGraph);
if(!edgeExists)
    boost::add_edge(v0 , v1, customGraph);

// write graph to console
cout << "\n-- graphviz output START --" << endl;
boost::write_graphviz(cout, customGraph);
cout << "\n-- graphviz output END --" << endl;