> My problem: size of the finishingOrder vector is zero outside the
> my_visitor::finish_vertex method. I checked its size inside the
> my_visitor::finish_vertex method and its value is increasing...

All visitors have to be copy constructible and depth_first_search will
operate on the copied object.
 
Actually, it's the fact that the visitor is copied that's causing the problem. The visitor needs to declare
it's vector member as a reference (to a vector declared somewhere else). For example:

struct my_visitor : default_dfs_visitor {
  my_visitor(vector<Vertex>& order)
    : finishingOrder(order)
  { }
  vector<Vertex>& finishingOrder;
};

Andrew Sutton
andrew.n.sutton@gmail.com