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# Daylight Savings Time-determining the dates when the switch occurs

Posted on 2003-12-01
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I was wondering if there were any vb functions or tricks to finding out the day the time changes in a given year.

In my program I need to know which day the time changes so my program can adapt its routines to account for the time change in its calculations.

if someone knows a quick way to do this that would be great.

Kelly
0
Question by:unreal400
• 2

LVL 9

Expert Comment

ID: 9852528
For the states which use daylight savings time, it starts at midnight on the first sunday in april, and ends at midnight on the last sunday in october.

0

LVL 9

Expert Comment

ID: 9852655
These functions return the start and end date for daylight savings time.

Private Function FirstSunApril(p_lYear As Long) As Date

Dim d1stOfMonth As Date
d1stOfMonth = CDate("4/1/" & p_lYear)

Dim d1stSunday  As Date
If Weekday(d1stOfMonth) = 1 Then
d1stSunday = d1stOfMonth
Else
d1stSunday = DateAdd("d", 8 - Weekday(d1stOfMonth), d1stOfMonth)
End If

FirstSunApril = d1stSunday

End Function

Private Function LastSunOct(p_lYear As Long) As Date

Dim dLastOfMonth As Date
dLastOfMonth = CDate("10/31/" & p_lYear)

Dim dLastSunday  As Date
If Weekday(dLastOfMonth) = 1 Then
dLastSunday = dLastOfMonth
Else
dLastSunday = DateAdd("d", -1 * (Weekday(dLastOfMonth) - 1), dLastOfMonth)
End If

LastSunOct = dLastSunday

End Function
0

LVL 26

Accepted Solution

EDDYKT earned 20 total points
ID: 9852717
You use this

Replace 2003 to any year you want

Option Explicit

Private Sub Command1_Click()
Debug.Print CalcDayLightBoundary(2003, 4, 1)
Debug.Print CalcDayLightBoundary(2003, 10, 2)
End Sub
Private Function CalcDayLightBoundary(Yr As Integer, Mon As Integer, Hr As Integer) As Date
Dim tt As Date, NumDays As Integer

On Error Resume Next
tt = DateSerial(Yr, Mon, 1) + TimeSerial(Hr, 0, 0)
NumDays = IIf(Weekday(tt) = 1, 0, 7 - Weekday(tt) + 1)
If (Mon = 10) Then
NumDays = NumDays + 28
If (NumDays > 31) Then NumDays = NumDays - 7
End If
End Function
0

LVL 2

Author Comment

ID: 9852848
Thanks EDDYKT  that was exactly what I was looking for.

Kelly
0

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