char * tzname [2] ¶The array tzname contains two strings, which are the standard
abbreviations of the pair of time zones (standard and Daylight
Saving) that the user has selected. tzname[0] abbreviates
the standard time zone (for example, "EST"), and tzname[1]
abbreviates the time zone when Daylight Saving Time is in use (for
example, "EDT"). These correspond to the std and dst
strings (respectively) from the TZ environment variable. If
Daylight Saving Time is never used, tzname[1] is the empty string.
The tzname array is initialized from the TZ environment
variable whenever tzset, ctime, strftime,
mktime, or localtime is called. If multiple abbreviations
have been used (e.g. "EWT" and "EDT" for U.S. Eastern War
Time and Eastern Daylight Time), the array contains the most recent
abbreviation.
The tzname array is required for POSIX.1 compatibility, but in
GNU programs it is better to use the tm_zone member of the
broken-down time structure, since tm_zone reports the correct
abbreviation even when it is not the latest one.
Though the strings are declared as char * the user must refrain
from modifying these strings. Modifying the strings will almost certainly
lead to trouble.
void tzset (void) ¶Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | See POSIX Safety Concepts.
The tzset function initializes the tzname variable from
the value of the TZ environment variable. It is not usually
necessary for your program to call this function, because it is called
automatically when you use the other time conversion functions that
depend on the time zone.
The following variables are defined for compatibility with System V
Unix. Like tzname, these variables are set by calling
tzset or the other time conversion functions.
long int timezone ¶This contains the difference between UTC and the latest local standard
time, in seconds west of UTC. For example, in the U.S. Eastern time
zone, the value is 5*60*60. Unlike the tm_gmtoff member
of the broken-down time structure, this value is not adjusted for
daylight saving, and its sign is reversed. In GNU programs it is better
to use tm_gmtoff, since it contains the correct offset even when
it is not the latest one.
int daylight ¶This variable has a nonzero value if Daylight Saving Time rules apply. A nonzero value does not necessarily mean that Daylight Saving Time is now in effect; it means only that Daylight Saving Time is sometimes in effect.