std::chrono::year_month_weekday::year, std::chrono::year_month_weekday::month, std::chrono::year_month_weekday::weekday, std::chrono::year_month_weekday::index, std::chrono::year_month_weekday::weekday_indexed

From cppreference.com
 
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
 
 
constexpr std::chrono::year year() const noexcept;
(1) (since C++20)
constexpr std::chrono::month month() const noexcept;
(2) (since C++20)
constexpr std::chrono::weekday weekday() const noexcept;
(3) (since C++20)
constexpr unsigned index() const noexcept;
(4) (since C++20)
constexpr std::chrono::weekday_indexed weekday_indexed() const noexcept;
(5) (since C++20)

Retrieves the field values stored in this year_month_weekday object.

Return value

1) Returns the stored std::chrono::year value.
2) Returns the stored std::chrono::month value.
3) Returns the stored std::chrono::weekday value.
4) Returns the stored weekday index.
5) weekday()[index()]

Example

#include <cassert>
#include <chrono>
 
int main()
{
    constexpr auto ym{std::chrono::year(2021)/std::chrono::January};
    constexpr auto wdi{std::chrono::Wednesday[1]};
    auto ymwdi{ym/wdi};
    const auto index{ymwdi.index() + 1};
    auto weekday{ymwdi.weekday() + std::chrono::days(1)};
    ymwdi = {ymwdi.year()/ymwdi.month()/weekday[index]};
    // Second Thursday in January, 2021
    assert(std::chrono::year_month_day{ymwdi} == std::chrono::January/14/2021);
}