Time Zone Information API

[crwreu]

I have two questions relating to the Time Zone Info API;

1. how do I get the "current" time zone setting, and

2. standard & daylight dates are relative dates .. relative to what?

Thank you in advance, Bob.

[jim mcnamara]

Private Const TIME_ZONE_ID_UNKNOWN As Long = 1
Private Const TIME_ZONE_ID_STANDARD As Long = 1
Private Const TIME_ZONE_ID_DAYLIGHT As Long = 2
Private Const TIME_ZONE_ID_INVALID As Long = &HFFFFFFFF

Private Type SYSTEMTIME
   wYear         As Integer
   wMonth        As Integer
   wDayOfWeek    As Integer
   wDay          As Integer
   wHour         As Integer
   wMinute       As Integer
   wSecond       As Integer
   wMilliseconds As Integer
End Type

Private Type TIME_ZONE_INFORMATION
   Bias As Long
   StandardName(0 To ((32 * 2) - 1)) As Byte
   StandardDate As SYSTEMTIME
   StandardBias As Long
   DaylightName(0 To ((32 * 2) - 1)) As Byte
   DaylightDate As SYSTEMTIME
   DaylightBias As Long
End Type

Private Declare Function GetTimeZoneInformation Lib "kernel32" _
    (lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long



Private Sub Command1_Click()
   Dim tmp
   tmp = Format$(Now, "hh:mm:ss AMPM")
   Text1.Text = tmp & " " & GetCurrentTimeZone()


End Sub


Private Function IsDaylightSavingTime() As Boolean

   Dim tzi As TIME_ZONE_INFORMATION

   IsDaylightSavingTime = GetTimeZoneInformation(tzi) = TIME_ZONE_ID_DAYLIGHT

End Function


Private Function GetCurrentTimeZone() As String

   Dim tzi As TIME_ZONE_INFORMATION
   Dim tmp As String
   Dim pos As Integer
   Select Case GetTimeZoneInformation(tzi)
      Case 0:  tmp = "Cannot determine current time zone"
      Case 1:  tmp = tzi.StandardName
      Case 2:  tmp = tzi.DaylightName
   End Select
   pos = InStr(tmp, Chr$(0))
   If pos Then
         tmp = Left$(tmp, pos - 1)
    Else
         tmp = item
    End If
  
   GetCurrentTimeZone = tmp
   
End Function

Daylight and standard time zones are set relative to your longitude - how far West or East you are from GMT (Greenwich Mean Time). 15 degrees of longitude is one hour - so most time zones are about that wide. Some time zones are on a 7.5 degree boundary - Macao for instance.

[crwreu]

Jim

From this code segment;

Select Case GetTimeZoneInformation(tzi)
Case 0: tmp = "Cannot determine current time zone"
Case 1: tmp = tzi.StandardName
Case 2: tmp = tzi.DaylightName
End Select

am I correct to assume that the API returns 0 if unsuccessful, 1 if standard time in use and 2 if daylight time in use? If so, this isn't in my documentation.

[jim mcnamara]

I believe it is correct, since it has worked for a long time...

[crwreu]

Thanks Jim, Bob.