[string.view.io]

template<class charT, class traits>
  basic_ostream<charT, traits>&
    operator<<(basic_ostream<charT, traits>& os,
               basic_string_view<charT, traits> str);

Effects: Behaves as a formatted output function ([ostream.formatted.reqmts]) of os.

Forms a character sequence seq, initially consisting of the elements defined by the range [str.begin(), str.end()).

Determines padding for seq as described in [ostream.formatted.reqmts].

Then inserts seq as if by calling os.rdbuf()->sputn(seq, n), where n is the larger of os.width() and str.size(); then calls os.width(0).

24 Strings library [strings]

24.4 String view classes [string.view]

24.4.4 Inserters and extractors [string.view.io]