std::chrono::year_month_day_last(3)

NAME
std::chrono::year_month_day_last - std::chrono::year_month_day_last

Synopsis
   Defined in header <chrono>
   class year_month_day_last; (since C++20)
   The class year_month_day_last represents the last day of a specific year and month.
   It is a field-based time point, with a resolution of std::chrono::days, subject to
   the limit that it can only represent the last day of a month.
   std::chrono::years- and std::chrono::months-oriented arithmetic are supported
   directly. An implicit conversion to std::chrono::sys_days allows
   std::chrono::days-oriented arithmetic to be performed efficiently.
   year_month_day_last is a TriviallyCopyable StandardLayoutType.

Member functions
   constructor constructs a year_month_day_last object
                       (public member function)
   operator+= modifies the time point by some number of months or years
   operator-= (public member function)
   year
   month accesses the fields of this object
   day (public member function)
   month_day_last
   operator sys_days converts to a std::chrono::time_point
   operator local_days (public member function)
   ok checks whether this object represents a valid date
                       (public member function)
  Nonmember functions
   operator== compares two year_month_day_last values
   operator<=> (function)
   (C++20)
   operator+ adds or subtracts a year_month_day_last and some number of years or
   operator- months
   (C++20) (function)
   operator<< outputs a year_month_day_last into a stream
   (C++20) (function template)

Helper classes
                        specialization of std::formatter
   std::formatter<std::chrono::year_month_day_last> that formats a year_month_day_last
   (C++20) according to the provided format
                        (class template specialization)

Example
// Run this code
 #include <iostream>
 #include <chrono>
 // until online compiler supports streaming the year_month_day_last:
 std::ostream& operator<< (std::ostream& os, std::chrono::year_month_day_last ymdl) {
     return os << static_cast<int>(ymdl.year()) << '/'
               << static_cast<unsigned>(ymdl.month()) << '/'
               << static_cast<unsigned>(ymdl.day());
 }
 int main()
 {
     const auto ymd = std::chrono::year_month_day{
         std::chrono::floor<std::chrono::days>(
             std::chrono::system_clock::now()
         )
     };
     const std::chrono::year_month_day_last ymdl{
         ymd.year(), ymd.month() / std::chrono::last
     };
     std::cout << "The date of the last day of this month is: " << ymdl << '\n';
     // The `last` object can be places wherever it is legal to place a `day`:
     using namespace std::chrono;
     constexpr std::chrono::year_month_day_last
         ymdl1 = 2023y / February / last,
         ymdl2 = last / February / 2023y,
         ymdl3 = February / last / 2023y;
     static_assert( ymdl1 == ymdl2 and ymdl2 == ymdl3 );
 }

Possible output:
 The date of the last day of this month is: 2021/11/30

See also
   year_month_day represents a specific year, month, and day
   (C++20) (class)