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title _daylight, _dstbias, _timezone, and _tzname | Microsoft Docs
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ms.date 11/04/2016
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cpp-standard-libraries
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f1_keywords
tzname
_timezone
timezone
_daylight
_tzname
daylight
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C++
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time zones
time adjustments
timezone variables
_tzname function
_daylight function
_timezone function
daylight function
local time adjustments
timezone function
tzname function
time-zone variables
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_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.

Syntax

extern int _daylight;   
extern int _dstbias;   
extern long _timezone;   
extern char *_tzname[2];

Remarks

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).

See Also

Global Variables
_get_daylight
_get_dstbias
_get_timezone
_get_tzname