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