boost dijkstra获得两点间的最短路

需求是只需要得到两点间的最短路，不需要求得单源对于全图的最短路，使用boost中的dijsktra_shortest_path，当得到目标点的最短路时直接throw exception。

 #include <boost/config.hpp>
 #include <iostream>

 #include <boost/graph/graph_traits.hpp>
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/graph/dijkstra_shortest_paths.hpp>

 using namespace boost;

 // define visitor for discover_vertex event

 template <class Vertex, class Tag>
 struct target_visitor : public default_dijkstra_visitor
 {
  target_visitor(Vertex u) : v(u) { }

  template <class Graph>
  void examine_vertex(Vertex u, Graph& g)
  {
   if( u == v ) {
    throw(-);
   }
  }
 private:
  Vertex v;
 };

 template <class Vertex, class Tag>
 target_visitor<Vertex, Tag>
 target_visit(Vertex u, Tag) {
  return target_visitor<Vertex, Tag>(u);
 }

 int main(int argc, char** argv)
 {
  typedef adjacency_list < listS, vecS, directedS,
   no_property, property < edge_weight_t, int > > graph_t;
  typedef graph_traits < graph_t >::vertex_descriptor vertex_descriptor;
  typedef graph_traits < graph_t >::edge_descriptor edge_descriptor;
  typedef std::pair<int, int> Edge;

  const int num_nodes = ;
  enum nodes { A, B, C, D, E };
  char name[] = "ABCDE";
  Edge edge_array[] =
  {
   Edge(A, C), Edge(B, B), Edge(B, D), Edge(B, E),
      Edge(C, B), Edge(C, D), Edge(D, E), Edge(E, A), Edge(E, B)
  };
   int weights[] = { , , , , , , , ,  };
  int num_arcs = sizeof(edge_array) / sizeof(Edge);

  graph_t g(edge_array, edge_array + num_arcs, weights, num_nodes);
  property_map<graph_t, edge_weight_t>::type weightmap = get(edge_weight, g);

  std::vector<vertex_descriptor> p(num_vertices(g));
  std::vector<int> d(num_vertices(g));

  // choose source and target
  vertex_descriptor src = vertex(A, g);
  vertex_descriptor targ = vertex(C, g);

  try {
   dijkstra_shortest_paths(g, src,
       predecessor_map(&p[]).distance_map(&d[]).visitor(target_visit(targ,
       on_examine_vertex())));
  }
  catch( ... ) {
  }

  std::cout << "distances and parents:" << std::endl;
  graph_traits < graph_t >::vertex_iterator vi, vend;
  for (tie(vi, vend) = vertices(g); vi != vend; ++vi) {
   std::cout << "distance(" << name[*vi] << ") = " << d[*vi] << ", ";
   std::cout << "parent(" << name[*vi] << ") = " << name[p[*vi]] << std::endl;
  }

     system("PAUSE");
  return EXIT_SUCCESS;
 }