Defined in header <chrono>
template< class CharT, class Traits >
std::basic_ostream<CharT, Traits>&
operator<<( std::basic_ostream<CharT, Traits>& os,
            const std::chrono::year_month_day& ymd );
(since C++20)

Outputs a textual representation of ymd into the stream os. This first forms a std::basic_string<CharT> s consisting of a textual representation of the date in the format yyyy-mm-dd (same as the one output by formatter with the %F specifier). Then, if !ymd.ok(), appends " is not a valid date" to s. Inserts s into os.

Equivalent to.

return os << (ymd.ok() ?
std::format(os.getloc(), STATICALLY_WIDEN<CharT>("{:%F}"), ymd) :
std::format(os.getloc(), STATICALLY_WIDEN<CharT>("{:%F} is not a valid date"), ymd));

where STATICALLY_WIDEN<CharT>("...") is "..." if CharT is char, and L"..." if CharT is wchar_t.

Return value



See also

stores formatted representation of the arguments in a new string
(function template)
formatting support for year_month_day
(class template specialization)

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