std::chrono::operator<<(std::chrono::year_month_day_last)
From cppreference.com
                    
                                        
                    < cpp | chrono | year month day last
                    
                                                            
                    |   Defined in header  <chrono>
  | 
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|   template< class CharT, class Traits > std::basic_ostream<CharT, Traits>&  | 
(since C++20) | |
Outputs a textual representation of ymdl into os, as if by
os << std::format(os.getloc(), STATICALLY_WIDEN<CharT>("{}/{:L}"),
                  ymdl.year(), ymdl.month_day_last());
where STATICALLY_WIDEN<CharT>("{}/{:L}") is "{}/{:L}" if CharT is char, and L"{}/{:L}" if CharT is wchar_t.
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
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See also
|    (C++20)  | 
   stores formatted representation of the arguments in a new string   (function template)  | 
   specialization of std::formatter that formats a year_month_day according to the provided format  (class template specialization)  |