On 10/27/2010 10:08 AM, Jeremiah Willcock wrote:
On Wed, 27 Oct 2010, langermatze wrote:
I tried this:
typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS> Graph; typedef typename boost::graph_traits<Graph>::degree_size_type (*FuncPtrType)(typename boost::graph_traits<Graph>::vertex_descriptor, const Graph &);
FuncPtrType funcPtr = boost::in_degree<Graph>;
The error I'm getting: error: no matches converting function ‘in_degree’ to type ‘size_t (*)(long unsigned int, const class boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, boost::no_property, boost::no_property, boost::no_property, boost::listS>&)’ /usr/include/boost/graph/detail/adjacency_list.hpp:1058: error: candidates are: template<class Config> typename Config::degree_size_type boost::in_degree(typename Config::vertex_descriptor, const boost::undirected_graph_helper<C>&) /usr/include/boost/graph/detail/adjacency_list.hpp:1649: error: template<class Config> typename Config::degree_size_type boost::in_degree(typename Config::vertex_descriptor, const boost::directed_edges_helper<Config>&)
Sounds reasonable since the signature of in_degree is way more complex than my function pointer signature. I couldn't find a way to get the correct Config template for my Graph class, that's why I tried to pass the Graph class itself but apparently that's not how it works.
I also tried casting which ends up in the "improper use of overloaded function" error that you mentioned:
FuncPtrType funcPtr = static_cast<FuncPtrType>(boost::in_degree<Graph>);
error: invalid static_cast from type ‘<unresolved overloaded function type>’ to type ‘size_t (*)(long unsigned int, const boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, boost::no_property, boost::no_property, boost::no_property, boost::listS>&)’
As for your concerns about efficiency, I'd ultimately use the function pointer as an additional template for the visitor which then shouldn't affect code efficiency at all but avoid code duplication only.
If you're doing that, you might as well make your own function objects (that are not function pointers) that call in_degree and/or out_degree directly in their operator()() implementations. That will be faster and avoid the casting problems you are having.
-- Jeremiah Willcock
Thanks for this hint, Jeremiah! I haven't used function objects so far. It seems like the function object cannot be used as a template parameter directly: template<typename Graph, typename NodeProperty, boost::function<NodeProperty (const typename boost::graph_traits<Graph>::vertex_descriptor&, const Graph&)> func> struct dfs_find_max_node_property_func: public boost::default_dfs_visitor { [...] } error: ‘struct boost::function<NodeProperty ()(const typename boost::graph_traits<G>::vertex_descriptor&, const Graph&), std::allocator<void> >’ is not a valid type for a template constant parameter What happens if the function object is passed to the constructor of the dfs visitor and stored as a member variable. If this function object is called somewhere in a member function of the visitor is it actually as fast as calling the corresponding boost function directly? If the function object cannot be passed as template it seems like it is not completely known at compile. I highly doubt that the call of the function object is actually inlined. template<typename Graph, typename NodeProperty> struct dfs_find_max_node_property_func: public boost::default_dfs_visitor { public: typedef typename boost::graph_traits<Graph>::vertex_descriptor NodeId; typedef typename boost::function<NodeProperty (const NodeId&, const Graph&)> FuncType; dfs_find_max_node_property_func(FuncType f) : func(f) { }; NodeProperty some_member(const NodeId &id, const Graph &g) { return func(id,g); } NodeProperty some_other_member(const NodeId &id, const Graph &g) { return boost::in_degree(id,g); } private: FuncType func; [...] } template<class Graph> struct foo { typename boost::graph_traits<Graph>::degree_size_type operator()(const typename boost::graph_traits<Graph>::vertex_descriptor &id, const Graph &g) const { return boost::in_degree(id, g); } }; dfs_find_max_node_property_func<Graph, boost::graph_traits<Graph>::degree_size_type> dfs_find_max_in_degree(foo()); I am wondering if dfs_find_max_node_property_func::some_member and dfs_find_max_node_property_func::some_other_member really perform equally well despite the additional function object wrapping. ~Matthias