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std::chrono...day::weekday(3) C++ Standard Libarystd::chrono...day::weekday(3)

NAME
       std::chrono::weekday::weekday - std::chrono::weekday::weekday

Synopsis
	  weekday()			    =			      default;
       (1) (since C++20)
	  explicit   constexpr	  weekday(    unsigned	  wd	)    noexcept;
       (2) (since C++20)
	  constexpr  weekday(  const  std::chrono::sys_days&  dp  )  noexcept;
       (3) (since C++20)
	  explicit constexpr  weekday(	const  std::chrono::local_days&	 dp  )
       (4) (since C++20)
	  noexcept;

	  Constructs a weekday object.

	  1) Default constructor leaves	the weekday value uninitialized.
	  2)  Constructs  a weekday object holding the weekday value wd. If wd
       == 7, the value
	  held is 0. If	wd > 255, the value held is unspecified.
	  3) Constructs	a weekday object representing the day of the  week  dp
       corresponds to.
	  This	  constructor	 defines    an	  implicit   conversion	  from
       std::chrono::sys_days to
	  weekday.
	  4) Constructs	a weekday object representing the day of the  week  dp
       corresponds to,
	  as if	by weekday(std::chrono::sys_days(dp.time_since_epoch())).

Example
       // Run this code

	#include <chrono>
	#include <iostream>
	#include <iomanip>

	int main()
	{
	    constexpr std::chrono::weekday friday{5};  // uses overload	(2)
	    static_assert(friday == std::chrono::Friday);

	    for	(int y {2020}; y <= 2023; ++y) {
		const std::chrono::year	cur_year{y};
		for (int cur_month{1}; cur_month != 13;	++cur_month) {
		    const    std::chrono::year_month_day   ymd{	  cur_year   /
       cur_month / 13 };
		    const	   std::chrono::weekday		  cur_weekday{
       std::chrono::sys_days{ ymd } };	// (3)
		    if (cur_weekday == friday) {
		    //	std::cout << ymd << " is " << friday <<	'\n';
			std::cout << int(ymd.year()) <<	'-' << std::setw(2) <<
       std::setfill('0')
				  << unsigned(ymd.month()) << '-'
				  << unsigned(ymd.day()) << " is Fri\n";
		    }
		}
	    }
	}

Output:
	2020-03-13 is Fri
	2020-11-13 is Fri
	2021-08-13 is Fri
	2022-05-13 is Fri
	2023-01-13 is Fri
	2023-10-13 is Fri

http://cppreference.com		  2022.07.31	 std::chrono...day::weekday(3)

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<https://man.freebsd.org/cgi/man.cgi?query=std::chrono::weekday::weekday&sektion=3&manpath=FreeBSD+Ports+15.0>

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