basic_ostream& operator<(basic_ostream& (*pf)(basic_ostream&);
basic_ostream& operator<(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&);
basic_ostream& operator<(ios_base& (*pf)(ios_base&);
basic_ostream& operator<(basic_streambuf<charT, traits>* sb);
basic_ostream& operator<(nullptr_t);