c++ - A question related to deriving standard exception classes -

  / * User-defined exceptions class has been derived from the standard class for exceptions * / classes MyProblem: public Std :: exception {public: ... MyProblem (...) {// Special Constructor} Virtual Cons 4 * what () const throw () {// what () function ...}}; ... zero F () {... // Create an Exception object and throw it Mayport (...); ...}  

My question is why after "const throw" () what is that? Generally, if there is a throw (), then it means that before the throw () () the function can remove the exception. Still, why throws here?