std::chrono::year_month_weekday:: operator sys_days, std::chrono::year_month_weekday:: operator local_days

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C-style date and time
std::chrono::year_month_weekday
constexpr operator std:: chrono :: sys_days ( ) const noexcept ;
(1) (since C++20)
constexpr explicit operator std:: chrono :: local_days ( ) const noexcept ;
(2) (since C++20)

Converts * this to a std::chrono::time_point representing the same date as this year_month_weekday .

1) If year ( ) . ok ( ) && month ( ) . ok ( ) && weekday ( ) . ok ( ) :
  • If index ( ) == 0 , returns a sys_days that represents the date 7 days prior to the first weekday() of the year and month.
  • Else, returns a sys_days that represents the date ( index ( ) - 1 ) * 7 days after the first weekday() of the year and month.
Otherwise, the returned value is unspecified.
2) Same as (1) , but returns local_days instead of sys_days . Equivalent to local_days ( sys_days ( * this ) . time_since_epoch ( ) ) .

Example

Run this code 
#include <chrono>
#include <iostream>
using namespace std::chrono;
 
int main()
{
    constexpr auto ymwd{Tuesday[2]/11/2021};
    std::cout << ymwd << '\n';
    // convert from field-based to serial-based to add hours
    constexpr auto sd = sys_days{ymwd} + 24h;
    std::cout << sd << '\n';
    constexpr auto ymd = floor<days>(sd);
    static_assert(ymd == November/10/2021);
}

Output: 

2021/Nov/Tue[2]
2021-11-10 00:00:00
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