Next: Time Functions Example, Previous: TZ Variable, Up: Calendar Time
The array
tznamecontains 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"), andtzname[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 theTZenvironment variable. If Daylight Saving Time is never used,tzname[1]is the empty string.The
tznamearray is initialized from theTZenvironment variable whenevertzset,ctime,strftime,mktime, orlocaltimeis 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
tznamearray is required for POSIX.1 compatibility, but in GNU programs it is better to use thetm_zonemember of the broken-down time structure, sincetm_zonereports 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.
The
tzsetfunction initializes thetznamevariable from the value of theTZenvironment 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 thetm_gmtoffmember 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 usetm_gmtoff, since it contains the correct offset even when it is not the latest one.