ostream& operator<<(ostream& o, fix const& x);
istream& operator>>(istream& i, fix& x);
These two functions don't actually belong to the gstreams, they are here simply because they sometimes make the life a bit easier (without costing anything in executable size if they are left unused). Their purpose is to make the class fix capable of extracting/inserting with the notation
fix a_number = 0.3; cout << a_number; cin >> a_number;
in conjuction with the standard stream system. And, by the way, consequently also in conjuction with a gstream:
gstream gs; gs << a_number; gs >> a_number;
You are probably not interested in calling them with their function names, only with the <</>> operators, so this paragraph is written just to make you aware of the possibility of doing that.