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