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std::chrono:: operator<< (std::chrono::sys_time)

From cppreference.net
C++
Date and time library
std::chrono::system_clock
Defined in header <chrono>
template < class CharT, class Traits, class Duration >

std:: basic_ostream < CharT, Traits > &
operator << ( std:: basic_ostream < CharT, Traits > & os,

const std:: chrono :: sys_time < Duration > & tp ) ;
(1) (since C++20)
template < class CharT, class Traits, class Duration >

std:: basic_ostream < CharT, Traits > &
operator << ( std:: basic_ostream < CharT, Traits > & os,

const std:: chrono :: sys_days & tp ) ;
(2) (since C++20)

Outputs tp into the stream os .

1) Equivalent to: 
return os << std::format(os.getloc(), STATICALLY-WIDEN<CharT>("{:L%F %T}"), tp);

where STATICALLY_WIDEN < CharT > ( "{:L%F %T}" ) is "{:L%F %T}" if CharT is char , and L "{:L%F %T}" if CharT is wchar_t .

This overload participates in overload resolution only if std:: chrono :: treat_as_floating_point_v < typename Duration :: rep > is false and Duration ( 1 ) < std:: chrono :: days ( 1 ) .
2) Equivalent to os << std:: chrono :: year_month_day ( tp ) ; .

Return value

os

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2372R3 C++20 the given locale was used by default L is needed to use the given locale

See also

(C++20)
formatting support for sys_time
(class template specialization)
(C++20)
stores formatted representation of the arguments in a new string
(function template)
(C++20)
outputs a year_month_day into a stream
(function template)