GNU Info

(libc.info)Time Zone Functions

---

Next: Time Functions Example Prev: TZ Variable Up: Calendar Time

---

Enter node , (file) or (file)node

Functions and Variables for Time Zones
--------------------------------------

 - Variable: char * tzname [2]
     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.


 - Function: void tzset (void)
     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.

 - Variable: 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.

 - Variable: 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.