_daylight, _dstbias, _timezone, and _tzname
_daylight, _dstbias, _timezone, and _tzname are used in some time and date routines to make local-time adjustments. These global variables have been deprecated for the more secure functional versions, which should be used in place of the global variables.
They are declared in Time.h as follows.
On a call to _ftime, localtime, or _tzset, the values of _daylight, _dstbias, _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 the default settings of "PST" and "PDT" respectively. The time-manipulation functions (_tzset, _ftime, and localtime) attempt to set the values of _daylight, _dstbias and _timezone by querying the operating system for the default value of each variable. The time-zone global variable values are shown in the following table.
Nonzero if daylight saving time (DST) zone is specified in TZ or determined from the operating system; otherwise, 0. The default value is 1.
Offset for daylight saving time.
Difference in seconds between coordinated universal time and local time. The default value is 28,800.
Time-zone name derived from the TZ environment variable. The default value is "PST".
DST zone name derived from the TZ environment variable. The default value is "PDT" (Pacific daylight time).