Question

I am quite new to Boost graph. I am trying to adapt an example for finding Dijkstra Shortest Path algorithm which used VertexList = vecS. I changed the vertex container to ListS. I learned that we have to provide our own vertex_index for the algorithm to work if we use listS.

int main(int, char *[])
{
  typedef float Weight;
  typedef boost::property<boost::edge_weight_t, Weight> WeightProperty;
  typedef boost::property<boost::vertex_name_t, std::string> NameProperty;
  typedef boost::property<boost::vertex_index_t, int> IndexProperty;

  typedef boost::adjacency_list < boost::listS, boost::listS, boost::directedS,
  NameProperty, WeightProperty > Graph;

  typedef boost::graph_traits < Graph >::vertex_descriptor Vertex;
  typedef boost::graph_traits <Graph>::vertex_iterator Viter;

  typedef boost::property_map < Graph, boost::vertex_index_t >::type IndexMap;
  typedef boost::property_map < Graph, boost::vertex_name_t >::type NameMap;

  typedef boost::iterator_property_map < Vertex*, IndexMap, Vertex, Vertex& > PredecessorMap;
  typedef boost::iterator_property_map < Weight*, IndexMap, Weight, Weight& > DistanceMap;

  Graph g;


  Vertex v0 = boost::add_vertex(std::string("v0"), g);
  Vertex v1 = boost::add_vertex(std::string("v1"), g);
  Vertex v2 = boost::add_vertex(std::string("v2"), g);
  Vertex v3 = boost::add_vertex(std::string("v3"), g);

  Weight weight0 = 5;
  Weight weight1 = 3;
  Weight weight2 = 2;
  Weight weight3 = 4;

  boost::add_edge(v0, v1, weight0, g);
  boost::add_edge(v1, v3, weight1, g);
  boost::add_edge(v0, v2, weight2, g);
  boost::add_edge(v2, v3, weight3, g);


  std::vector<Vertex> predecessors(boost::num_vertices(g)); // To store parents
  std::vector<Weight> distances(boost::num_vertices(g)); // To store distances

  IndexMap indexMap; // = boost::get(boost::vertex_index, g);
  NameMap name;
  Viter i, iend;
 //Create our own vertex index. This is what I changed in the original code
    int c = 0;
  for (boost::tie(i, iend) = vertices(g); i != iend; ++i, ++c) {
       indexMap[*i] = c; // **Error points to this line**
       name[*i] = 'A' + c;
  }
PredecessorMap predecessorMap(&predecessors[0], indexMap);
DistanceMap distanceMap(&distances[0], indexMap);
boost::dijkstra_shortest_paths(g, v0,   boost::distance_map(distanceMap).predecessor_map(predecessorMap));


  // Extract a shortest path
  std::cout << std::endl;
  typedef std::vector<Graph::edge_descriptor> PathType;
  PathType path;
  Vertex v = v3; 
  for(Vertex u = predecessorMap[v]; 
  u != v; // Keep tracking the path until we get to the source
  v = u, u = predecessorMap[v]) // Set the current vertex to the current predecessor,     and the predecessor to one level up
  {
     std::pair<Graph::edge_descriptor, bool> edgePair = boost::edge(u, v, g);
    Graph::edge_descriptor edge = edgePair.first;
    path.push_back( edge );
  }

  // Write shortest path
  std::cout << "Shortest path from v0 to v3:" << std::endl;
  float totalDistance = 0;
  for(PathType::reverse_iterator pathIterator = path.rbegin(); pathIterator !=       path.rend(); ++pathIterator)
  {
    std::cout << name[boost::source(*pathIterator, g)] << " -> " <<     name[boost::target(*pathIterator, g)]
              << " = " << boost::get( boost::edge_weight, g, *pathIterator ) <<     std::endl;

  }

  std::cout << std::endl;

  std::cout << "Distance: " << distanceMap[v3] << std::endl;

  return EXIT_SUCCESS;
}

I get the following error:

/spvec.cpp:62:20: error: no match for ‘operator=’ in ‘index.boost::adj_list_vertex_property_map::operator[] [with Graph = boost::adjacency_list >, boost::property >, ValueType = boost::detail::error_property_not_found, Reference = boost::detail::error_property_not_found&, Tag = boost::vertex_index_t, boost::adj_list_vertex_property_map::key_type = void*](i.std::_List_iterator<_Tp>::operator* with _Tp = void*, _Tp& = void*&) = c’

I am sure I made a mistake in creating my own vertex index. But couldn´t find out exactly what´s the issue. Does anyone have some suggestions on what I am doing wrong..

Answer 1

BGL actually has an example of using dijkstra_shortest_paths with listS/listS, but it’s not linked to from the HTML documentation: http://www.boost.org/doc/libs/release/libs/graph/example/dijkstra-example-listS.cpp

What the error message is trying to tell you (error: no match for ‘operator=’ in ‘index.boost::adj_list_vertex_property_map...ValueType = boost::detail::error_property_not_found...) is that there is no per-vertex storage for the vertex_index_t property, which is what adj_list_vertex_property_map needs. To fix the problem you can either change your Graph typedef to include per-vertex storage for the vertex_index_t property or use an “external” property map such as associative_property_map.

The dijkstra-example-listS.cpp example uses the approach of changing the graph typedef. To use this approach in your code, you could define:

typedef boost::adjacency_list <boost::listS, boost::listS, boost::directedS,
  boost::property<boost::vertex_name_t, std::string, boost::property<boost::vertex_index_t, int> >,
  boost::property<boost::edge_weight_t, Weight> > Graph;