something weird about members of Time.h structure

Question

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Why does tm_sec range from 0-60 instead of 0-59 in time.h?

So when I looked up <time.h> for some info, I ran across this. I'm assuming the numbers in the square brackets are the ranges possible for each respective member of the structure. So why is there 0~61 possible range for seconds? Were there 62 seconds in each minute and I'm the only one who didn't know about it???

int    tm_sec   seconds [0,61] // <-- this part is weird
int    tm_min   minutes [0,59]
int    tm_hour  hour [0,23]
int    tm_mday  day of month [1,31]
int    tm_mon   month of year [0,11]
int    tm_year  years since 1900
int    tm_wday  day of week [0,6] (Sunday = 0)
int    tm_yday  day of year [0,365]
int    tm_isdst daylight savings flag

Answer 1

Leap seconds.