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Daylight Savings Time-determining the dates when the switch occurs

Posted on 2003-12-01
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Last Modified: 2010-05-01
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
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Question by:unreal400
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LVL 9

Expert Comment

by:dancebert
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.

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LVL 9

Expert Comment

by:dancebert
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
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Accepted Solution

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EDDYKT earned 80 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
    CalcDayLightBoundary = DateAdd("D", NumDays, tt)
End Function
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LVL 2

Author Comment

by:unreal400
ID: 9852848
Thanks EDDYKT  that was exactly what I was looking for.

Kelly
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