Daylight Savings Time detection

[AlphaScorpious]

I was working on an Excel file today in an attempt to automate most of it's requirements. One cell is required to have either PDT or PST depending upon what time of year it is. I could not find anything in VB 6 that tested the system clock to determine if the time of year was currently standard or daylight time so I wrote this:

Sub CheckPDT()
 
   'Holds the date for the start and end PDT
    Dim PDTStart As String
    Dim PDTEnd As String
    
    'These hold the values days, months, year, name of the day of the week, and the number of the day of the week
    Dim MyDay As String
    Dim MyMonth As String
    Dim MyYear As String
    Dim DayNum As String
    Dim TestMonth As Integer
    Dim TestDay As Integer
    
    'The date we are going to test
    Dim MyDate As String
    
    'Hold the difference between 2 dates
    Dim DiffApril As Integer
    Dim DiffOct As Integer
    
    'Set the initial TestMonth and TestDay for April 1
    TestMonth = 4
    TestDay = 1
    
    'Get the first Sunday in April by cycling thru the days beinning from the 1st
    Do Until MyDay = "Sunday"
        MyDate = CStr(TestMonth) & "/" & CStr(TestDay) & "/" & Year(Date)
        MyDate = DateValue(MyDate)
        DayNum = Day(MyDate)
        MyMonth = Month(MyDate)
        MyMonth = MonthName(MyMonth, False)
        MyDay = Weekday(MyDate)
        MyDay = WeekdayName(MyDay, False, 1)
        If MyDay = "Sunday" Then
            PDTStart = MyMonth & " " & DayNum & ", " & Year(Date)
            Exit Do
        End If
        TestDay = TestDay + 1
    Loop
    
    'Reset the TestMonth, TestDay  to October 31 and MyDay to nothing
    TestMonth = 10
    TestDay = 31
    MyDay = ""
    
    'Get the last Sunday in October by cycling backwards thru the days beginning with the 31st
    Do Until MyDay = "Sunday"
        MyDate = CStr(TestMonth) & "/" & CStr(TestDay) & "/" & Year(Date)
        MyDate = DateValue(MyDate)
        DayNum = Day(MyDate)
        MyMonth = Month(MyDate)
        MyMonth = MonthName(MyMonth, False)
        MyDay = Weekday(MyDate)
        MyDay = WeekdayName(MyDay, False, 1)
        If MyDay = "Sunday" Then
            PDTEnd = MyMonth & " " & DayNum & ", " & Year(Date)
            Exit Do
        End If
        TestDay = TestDay - 1
    Loop
    
    'Get the difference between today's date and the start and end of Daylight Savings Time
    DiffApril = Val(DateDiff("d", PDTStart, Date))
    DiffOct = Val(DateDiff("d", PDTEnd, Date))
    
    'Display the time
    If (DiffApril > 0) And (DiffOct < 0) Then
        MsgBox "The time is " & Time & " Pacific Daylight Time."
    Else
        MsgBox "The time is " & Time & " Pacific Standard Time."
    End If
 
End Sub

[Comintern]

Just found this trolling through the CodeBank and thought I'd post an API version of this in case anyone else needs it (much easier\faster).

Private Type TimeZoneInfo
    Bias As Long
    StandardName(63) As Byte
    StandardDate(7) As Integer
    StandardBias As Long
    DaylightName(63) As Byte
    DaylightDate(7) As Integer
    DaylightBias As Long
End Type
 
Private Const TIME_ZONE_ID_DAYLIGHT = 2
 
Private Declare Function GetTimeZoneInformation Lib "kernel32" (uTZ As TimeZoneInfo) As Long
 
Private Function IsDLSavings() As Boolean
 
    Dim uInfo As TimeZoneInfo, lReturn As Long
    
    lReturn = GetTimeZoneInformation(uInfo)
 
    If lReturn = TIME_ZONE_ID_DAYLIGHT Then
        IsDLSavings = True
    End If
 
End Function