29 Time library [time]

29.8 The civil calendar [time.cal]

29.8.7 Class weekday_indexed [time.cal.wdidx] Member functions [time.cal.wdidx.members]

constexpr weekday_indexed(const chrono::weekday& wd, unsigned index) noexcept;
Effects: Initializes wd_ with wd and index_ with index.
The values held are unspecified if !wd.ok() or index is not in the range [0, 7].
constexpr chrono::weekday weekday() const noexcept;
Returns: wd_.
constexpr unsigned index() const noexcept;
Returns: index_.
constexpr bool ok() const noexcept;
Returns: wd_.ok() && 1 <= index_ && index_ <= 5.