VBScript to determine if date is in DST

Windows Scripting Host

The function IsDST determines if any date is in the Daylight Savings Time
period as defined in the United States. To use this script for other
countries you will have to make appropriate adjustments for your locale.

The function returns a value of 0 for not in DST; 1 for in DST
and -1 if the date argument supplied is invalid.

The function requires two arguments:
A string date value
A one-dimensional two element array

The one-dimensional two element array returns two strings, the date DST begins in
the year specified in the date value, and the date DST ends for that same
year. The purpose of composing the script in this manner is to allow you
to not only determine if any date is within DST but also to allow you to
query the script with a date value to discover the range of DST dates for
any given year (to calculate, for example, how many days until DST begins
or ends). If this feature does not interest you simply ignore the values
returned in the array; however you must pass it a one-dimensional two element array
in any case.

Sample usage:

option explicit
Dim arrDST(1), x
x = IsDST(Date, arrDST)
wscript.echo x, arrDST(0), arrDST(1)

Sample output:
0 4/7/2002 10/27/2002

2007 rules compatabile version provided by Dan Gould. (Thanks Dan!)

' isDST() - Returns 1 if in DST, 0 if not, -1 on bad date
' - argDate: Today's date
' - argReturn: Two element array containing DST start and end dates

Function isDST(argDate, argReturn)
Dim StartDate, EndDate

If (Not IsDate(argDate)) Then
  argReturn(0) = -1
  argReturn(1) = -1
  isDST = -1
  Exit Function
End If

' DST start date...
StartDate = DateSerial(Year(argDate), 3, 1)
Do While (WeekDay(StartDate) <> vbSunday)
  StartDate = StartDate + 1
Loop
StartDate = StartDate + 7

' DST end date...
EndDate = DateSerial(Year(argDate), 11, 1)
Do While (WeekDay(EndDate) <> vbSunday)
  EndDate = EndDate + 1
Loop

  ' Finish up...
isDST = 0
If ((argDate >= StartDate) And (argDate < EndDate)) Then
  argReturn(0) = StartDate
  argReturn(1) = EndDate
  isDST = 1
End If
End Function

'Code begins here (Pre-2007 Version)

'IsDST.vbs
'=======================================
Function IsDST(TodayDate, arrReturn)
' Is any date in DST and dates DST begins and ends
' Args = Date, 1 dimensional two element array
' Returns -1 on error (bad date)
' 0 if NOT DST
' 1 If in DST
' -1 If date value is invalid
' arrRetunr(0) = First day of DST
' arrReturn(1) = Last day of DST
' Paul R. Sadowski <aa089(at)bfn.org>

Dim StartDate, EndDate, StartDOW, EndDOW, TargetDOW
Dim BeginDST, EndDST
if IsDate(TodayDate) <> True then
arrReturn(0) = -1
arrReturn(1) = -1
IsDST = -1
Exit Function
end if
StartDate = CDate("4/1/" & Cstr(Year(TodayDate)))
EndDate = CDate("11/1/" & Cstr(Year(TodayDate)))
StartDOW = Weekday(StartDate)
if StartDOW <> 1 then
TargetDOW = 8 - StartDOW
end if
BeginDST = DateAdd("d", TargetDOW, StartDate)
EndDOW = Weekday(EndDate)
if EndDOW <> 1 then
TargetDOW = 1 - EndDOW
end if
EndDST = DateAdd("d", TargetDOW, EndDate)
if DateDiff("d", BeginDST, TodayDate) >= 0 then
if DateDiff("d", EndDST, TodayDate) < 0 then
arrReturn(0) = BeginDST
arrReturn(1) = EndDST
IsDST = 1
Exit Function
end if
end if
arrReturn(0) = BeginDST
arrReturn(1) = EndDST
IsDST = 0
End Function