21. More things to watch out for

• 
  class Base {};
  
  class Derived : public Base {};
  
  void f( Base* bp );
  void g( Base  b  );
  void h( Derived* dp );
  
  Derived d;
  Base b;
  
  Base* bp = &d;       // OK
  
  f( bp );             // OK
  g( b );              // OK
  h( (Derived*) bp );  // Accepted, but not advised
  h( (Derived*) &b );  // Accepted, but surely wrong!