_daylight, _timezone, and _tzname
_daylight, _timezone, and _tzname are used in some time and date routines to make local-time adjustments. They are declared in TIME.H as:
extern int _daylight; extern long _timezone; extern char *_tzname;
On a call to _ftime, localtime, or _tzset, the values of _daylight, _timezone, and _tzname are determined from the value of the TZ environment variable. If you do not explicitly set the value of TZ, _tzname and _tzname contain empty strings, but the time-manipulation functions (_tzset, _ftime, and localtime) attempt to set the values of _daylight and _timezone by querying the operating system for the default value of each variable. The time-zone global variable values are as follows.
|_daylight||Nonzero if daylight saving time (DST) zone is specified in TZ; otherwise, 0. Default value is 1.|
|_timezone||Difference in seconds between coordinated universal time and local time. Default value is 28,800.|
|_tzname||Time-zone name derived from TZ environment variable.|
|_tzname||DST zone name derived from TZ environment variable. Default value is PDT (Pacific daylight time). If DST zone is omitted from TZ, _tzname is empty string.|