#include <iostream>
#include <map>
#include <vector>
#include <boost/shared_ptr.hpp>
#include <boost/functional/hash.hpp>

int
main()
{
   typedef boost::shared_ptr<int> ptr_type;
   typedef std::map<std::size_t, int> hashes_type;
   std::vector<ptr_type> v(25);
   hashes_type hashes;
   boost::hash<ptr_type> hasher;
   ptr_type null_ptr;
   ++hashes[hasher(null_ptr)];
   for (int i(0); i < 25; ++i)
   {
      v[i] = ptr_type(new int(i));
      std::size_t const hash(hasher(v[i]));
      ++hashes[hash];
   }
   for (hashes_type::iterator it(hashes.begin()), end(hashes.end());
        it != end; ++it)
   {
      std::cout << it->first << ": " << it->second << '\n';
   }
}