tzset
—set timezone characteristics from TZ environment variable#include <time.h> void tzset(void); void _tzset_r (struct _reent *);
Description
tzset
examines the TZ environment variable and sets up the three
external variables: _timezone
, _daylight
, and tzname
. The
value of _timezone
shall be the offset from the current time zone
to GMT. The value of _daylight
shall be 0 if there is no daylight
savings time for the current time zone, otherwise it will be non-zero.
The tzname
array has two entries: the first is the name of the
standard time zone, the second is the name of the daylight-savings time
zone.
The TZ environment variable is expected to be in the following POSIX format:
stdoffset1[dst[offset2][,start[/time1],end[/time2]]]
where: std is the name of the standard time-zone (minimum 3 chars) offset1 is the value to add to local time to arrive at Universal time it has the form: hh[:mm[:ss]] dst is the name of the alternate (daylight-savings) time-zone (min 3 chars) offset2 is the value to add to local time to arrive at Universal time it has the same format as the std offset start is the day that the alternate time-zone starts time1 is the optional time that the alternate time-zone starts (this is in local time and defaults to 02:00:00 if not specified) end is the day that the alternate time-zone ends time2 is the time that the alternate time-zone ends (it is in local time and defaults to 02:00:00 if not specified)
Note that there is no white-space padding between fields. Also note that if TZ is null, the default is Universal GMT which has no daylight-savings time. If TZ is empty, the default EST5EDT is used.
The function _tzset_r
is identical to tzset
only it is reentrant
and is used for applications that use multiple threads.
Returns
There is no return value.
Portability
tzset
is part of the POSIX standard.
Supporting OS subroutine required: None