[Boost-users] Re: question about breadth_first_search

From: Christopher D. Russell (cdr_at_[hidden])
Date: 2005-01-05 12:06:09

Hi Matthias,

The only thing that's likely to be a little counter intuitive is that 
visitors are copied by value. Typically, instantiate your std::list (or 
whatever container you decide to use) just prior to instantiating your 
visitor and pass a non-const reference into the visitor's constructor.

e.g.

template  <typename VertexNameMap> class bfs_name_printer : public 
default_bfs_visitor
{
public:
explicit bfs_name_printer(VertexNameMap & _name_map) : name_map(_name_map) {}

private:
VertexNameMap & name_map;

// your visitor methods ...
};

... then

typdef std::list<foo_t> vertex_name_map_t;
vertex_name_map_t vertex_name_map;
bfs_name_printer<vertex_name_map_t> visitor(vertex_name_map);

... and so on.

HTH - Chris

"Matthias Linkenheil" <M.Linkenheil_at_[hidden]> wrote in message 
news:41DC1524.6010209_at_dkfz-heidelberg.de...
> Dear all,
>
> i want to use the breadth_first_search algorithm to store the visited nodes 
> e.g. in a list for access in the main function.
> Has anyone an idea to handle this?
> In my code i print out the visited nodes.
>
> The examples in the Boost User Guide about the visitor concept are 
> sometimes not so easy to understand.
>
> ...
> using namespace boost;
> template <typename VertexNameMap>
> class bfs_name_printer:public default_bfs_visitor {
> public:
>    bfs_name_printer(VertexNameMap n_map) : m_name_map(n_map){}
>    template <typename Vertex, typename Graph>
>        void discover_vertex(Vertex u, const Graph& ) const {
>            std::cout<<get(m_name_map, u) <<" ";
>        }
> private:
>    VertexNameMap m_name_map;
>
> };
> ...
>
> main(){
>
> ...
> typedef property_map<Graph, vertex_index_t>::type VertexNameMap;
> VertexNameMap id = get(vertex_index, g);
> bfs_name_printer<VertexNameMap> vis(id);
> breadth_first_search(fg, s, visitor(vis));
>
> ...
>
> Regards,
> Matthias