27 Time library [time]

27.11 Time zones [time.zone]

27.11.8 Class leap_­second [time.zone.leap]

27.11.8.2 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:
All leap seconds inserted up through 2019 were positive leap seconds.
— end note]