tzname contains two strings, which are the standard
abbreviations of the pair of time zones (standard and Daylight
Saving) that the user has selected.
the standard time zone (for example,
abbreviates the time zone when Daylight Saving Time is in use (for
"EDT"). These correspond to the std and dst
strings (respectively) from the
TZ environment variable. If
Daylight Saving Time is never used,
tzname is the empty string.
tzname array is initialized from the
localtime is called. If multiple abbreviations
have been used (e.g.
"EDT" for U.S. Eastern War
Time and Eastern Daylight Time), the array contains the most recent
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.
Preliminary: | MT-Safe env locale | AS-Unsafe heap lock | AC-Unsafe lock mem fd | See POSIX Safety Concepts.
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
tzname, these variables are set by calling
tzset or the other time conversion functions.
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
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
tm_gmtoff, since it contains the correct offset even when
it is not the latest one.
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.