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The array tzname
contains two strings, which are the standard
names of the pair of time zones (standard and Daylight
Saving) that the user has selected. tzname[0]
is the name of
the standard time zone (for example, "EST"
), and tzname[1]
is the name for 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.
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.
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.
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.
Next: Time Functions Example, Previous: TZ Variable, Up: Calendar Time [Contents][Index]