Defined in header
leap_second represents the date and time of a leap second insertion.
Users cannot construct
leap_second objects except by copying from existing
leap_second objects. The library implementation creates
leap_second objects when it initializes the time zone database and provides const access to these objects.
leap_second has a defaulted copy constructor and a defaulted copy assignment operator.
 Member functions
| obtains the time of leap second insertion |
(public member function)
 Nonmember functions
| compares two |