Function null_edge

Infovis/BoostGraphAlgorithms/vtkBoostGraphAdapter.h:454–454

  static vertex_descriptor null_vertex() { return -1; }
  typedef vtkEdgeType edge_descriptor;
  static edge_descriptor null_edge() { return vtkEdgeType(-1, -1, -1); }
  typedef vtk_out_edge_pointer_iterator out_edge_iterator;
  typedef vtk_in_edge_pointer_iterator in_edge_iterator;