_daylight, _dstbias, _timezone, and _tzname
The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.
The latest version of this topic can be found at _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.
| Global variable | Functional equivalent |
|---|---|
_daylight | _get_daylight |
_dstbias | _get_dstbias |
_timezone | _get_timezone |
_tzname | _get_tzname |
They are declared in Time.h as follows.
extern int _daylight; extern int _dstbias; extern long _timezone; extern char *_tzname[2];
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[0] and _tzname[1] 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.
| Variable | Value |
|---|---|
_daylight | Nonzero if daylight saving time (DST) zone is specified in TZ or determined from the operating system; otherwise, 0. The default value is 1. |
_dstbias | Offset for daylight saving time. |
_timezone | Difference in seconds between coordinated universal time and local time. The default value is 28,800. |
_tzname[0] | Time-zone name derived from the TZ environment variable. The default value is "PST". |
_tzname[1] | DST zone name derived from the TZ environment variable. The default value is "PDT" (Pacific daylight time). |
Global Variables
_get_daylight
_get_dstbias
_get_timezone
_get_tzname