Namespaces
Variants

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.net
C++
Date and time library
std::chrono::year_month_weekday
constexpr std:: chrono :: year year ( ) const noexcept ;
(1) (自 C++20 起)
constexpr std:: chrono :: month month ( ) const noexcept ;
(2) (自 C++20 起)
constexpr std:: chrono :: weekday weekday ( ) const noexcept ;
(3) (自 C++20 起)
constexpr unsigned index ( ) const noexcept ;
(4) (自 C++20 起)
constexpr std:: chrono :: weekday_indexed weekday_indexed ( ) const noexcept ;
(5) (自 C++20 起)

获取存储在此 year_month_weekday 对象中的字段值。

返回值

1) 返回存储的 std::chrono::year 值。
2) 返回存储的 std::chrono::month 值。
3) 返回存储的 std::chrono::weekday 值。
4) 返回存储的星期索引。
5) weekday ( ) [ index ( ) ]

示例

运行此代码 
#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]};
    // 2021年1月的第二个星期四
    assert(std::chrono::year_month_day{ymwdi} == std::chrono::January/14/2021);
}