[Boost-users] Boost Graph Library: edge retrieval using edge descriptor between square brackets fails

Subject: [Boost-users] Boost Graph Library: edge retrieval using edge descriptor between square brackets fails
From: Nicholas Mario Wardhana (mario.wardhana_at_[hidden])
Date: 2011-01-11 23:53:33

Hi all,

I am wrapping the Boost Graph Library with a thin class, and I am
having a problem in retrieving the edge. I use a mechanism similar to
the one in here:

http://stackoverflow.com/questions/3100146/adding-custom-vertices-to-a-boost-graph

For testing, I add two vertices (suppose pNode1 and pNode2)
successfully, and they can be retrieved as well by passing in their
vertex descriptors. However, this is not the case for the edges: when
I add an edge from pNode1 to pNode2, the edge is correctly stored as
the out_edge of pNode1, but when I retrieve the edge using its edge
descriptor, which is the (valid) return value of the add_edge()
function, the pointer value is NULL. Also, when I debug the code, I
find that inside the graph, there are two variables m_edges and
m_vertices. The m_vertices correctly contains two vertex descriptors,
but the m_edges is empty. So, do I make a mistake here? I have been
looking for some information in Boost's archive and other sources
(StackOverflow, ...), but so far haven't found anything helpful.

I include a snippet at the end of this e-mail. I am using Visual
Studio 2008 SP1 on Windows Vista SP2, and Boost 1.44.0 (haven't
upgraded yet to 1.45, but the latter doesn't seem to address this
issue).

Thank you!

Best regards,
Nicholas Mario Wardhana

//--------------------------- snippet -----------------------------

template <class NodeData, class EdgeData>
class BoostGraphWrapper : public Graph<NodeData, EdgeData>
{
   typedef boost::adjacency_list<boost::listS, boost::listS,
boost::directedS, Node<NodeData>*, Edge<NodeData, EdgeData>*,
boost::listS> BoostGraph;
   typedef typename boost::graph_traits<BoostGraph>::vertex_descriptor
BoostVertexDescriptor;
   typedef typename boost::graph_traits<BoostGraph>::edge_descriptor
BoostEdgeDescriptor;

   //...

public:
   void AddNode(Node<NodeData>* pNode);
   Edge<NodeData, EdgeData>* AddEdge(Node<NodeData>* pNode1,
Node<NodeData>* pNode2);

   //...

private:
   BoostGraph m_graph;

   //...
};

template <class NodeData, class EdgeData>
void BoostGraphWrapper<NodeData, EdgeData>::AddNode(Node<NodeData>* pNode)
{
   Graph<NodeData, EdgeData>::AddNode(pNode);

   // 1. Get the descriptor
   BoostVertexDescriptor vertexDescriptor = boost::add_vertex(m_graph);

   // 2. Fill with the node
   m_graph[vertexDescriptor] = pNode;

   // ...
}

template <class NodeData, class EdgeData>
Edge<NodeData, EdgeData>* BoostGraphWrapper<NodeData,
EdgeData>::AddEdge( Node<NodeData>* pNode1, Node<NodeData>* pNode2 )
{
   Graph<NodeData, EdgeData>::AddEdge(pNode1, pNode2);

   // 1. Get vertex descriptors of the nodes
   BoostVertexDescriptor vertexDescriptor1 = GetBoostVertexDescriptor(pNode1);
   BoostVertexDescriptor vertexDescriptor2 = GetBoostVertexDescriptor(pNode2);
   Node<NodeData>* tempNode = m_graph[vertexDescriptor1];
   Node<NodeData>* tempNode2 = m_graph[vertexDescriptor2];

   // 2. Add an empty edge
   BoostEdgeDescriptor edgeDescriptor;
   bool inGraph = false;
   boost::tie(edgeDescriptor,inGraph) =
boost::add_edge(vertexDescriptor1, vertexDescriptor2, m_graph);
   if(!inGraph)
   {
       return NULL;
   }
   assert(BoostEdgeSize() == 1); // successful

   // 3. Fill the edge with the vertices
   Edge<NodeData, EdgeData>* temp = m_graph[edgeDescriptor];
   assert(NULL != temp);  // fails here

   //....

   return pEdge;
}

void SomeFunction()
{
   BoostGraphWrapper<int, int> graphWrapper;
   Node<int>* pNode1 = new Node<int>();
   Node<int>* pNode2 = new Node<int>();
   Edge<int, int>* pEdge;

   graphWrapper.AddNode(pNode1);
   graphWrapper.AddNode(pNode2);

   pEdge = graphWrapper.AddEdge(pNode2, pNode1); // fails here
}