My time.h
has the following definition of tm
:
struct tm {
int tm_sec; /* seconds after the minute [0-60] */
int tm_min; /* minutes after the hour [0-59] */
int tm_hour; /* hours since midnight [0-23] */
...
}
I just noticed that they document tm_sec
as ranging between 0-60 inclusive. I've always assumed it ranged from 0-59 just like tm_min
. I've certainly never seen a clock read 10:37:60...
Do you think this is just a documentation bug left over from this 90's era Berkley-originated file?
Or is there something more subtle going on that I'm unaware of?
Leap seconds are the reason for this:
A leap second is a plus or minus one-second adjustment to the Coordinated Universal Time (UTC) time scale that keeps it close to mean solar time.
When a positive leap second is added at 23:59:60 UTC, it delays the start of the following UTC day (at 00:00:00 UTC) by one second, effectively slowing the UTC clock.
The man page for ctime
explains that this is about leap seconds:
tm_sec
: The number of seconds after the minute, normally in the range 0 to 59, but can be up to 60 to allow for leap seconds.
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