29 Time library [time]

29.11 Time zones [time.zone]

29.11.8 Class leap_second [time.zone.leap] Member functions [time.zone.leap.members]

constexpr sys_seconds date() const noexcept;
Returns: The date and time at which the leap second was inserted.
constexpr seconds value() const noexcept;
Returns: +1s to indicate a positive leap second or -1s to indicate a negative leap second.
[Note 1: 
All leap seconds inserted up through 2022 were positive leap seconds.
— end note]