Question

Ambiguous overload for operator<<() is called when I add the overload function below

template <typename Container> ostream& operator<<(ostream& os, const Container& c)  
  {  
  copy(c.begin(), c.end(), ostream_iterator<typename Container::value_type>(os, " "));  
  return os;  
  }

the error is called on this function where it uses the <<.

  void print_list(const list<int>& list_int)
    {
    for (list<int>::const_iterator it = list_int.begin(); it != list_int.end(); it++) cout << *it << " ";
    }

Answer 1

(For reference, if anyone else is looking: http://ideone.com/YlX7q )

Your definition of operator<< can be instantiated as ::operator<<<int>(std::ostream&, const int&); this is ambigious with std::operator<<(std::ostream&, int). Calling the name of the type Container doesn’t mean it is a container; overload resolution is done before the definition is instantiated.