VB and VBA Users Source Code: Converting local time to and from GMT
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VB/VBA Source Code
Converting local time to and from GMT
By:
Andrew Baker
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Date:
Friday, July 28, 2006
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9172
Category:
Visual Basic General
Article:
The code below shows how to convert local time to and from GMT time. Option Explicit 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(31) As Integer StandardDate As SYSTEMTIME StandardBias As Long DaylightName(31) As Integer DaylightDate As SYSTEMTIME DaylightBias As Long End Type Private Declare Function GetTimeZoneInformation Lib "kernel32" (lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long 'Purpose : Converts local time to GMT. 'Inputs : dtLocalDate The local data time to return as GMT. 'Outputs : Returns the local time in GMT. 'Author : Andrew Baker 'Date : 13/11/2002 10:16 'Notes : 'Revisions : Public Function ConvertLocalToGMT(dtLocalDate As Date) As Date Dim lSecsDiff As Long 'Get the GMT time diff lSecsDiff = GetLocalToGMTDifference() 'Return the time in GMT ConvertLocalToGMT = DateAdd("s", -lSecsDiff, dtLocalDate) End Function 'Purpose : Converts GMT time to local time. 'Inputs : dtLocalDate The GMT data time to return as local time. 'Outputs : Returns GMT as local time. 'Author : Andrew Baker 'Date : 13/11/2002 10:16 'Notes : 'Revisions : Public Function ConvertGMTToLocal(gmtTime As Date) As Date Dim Differerence As Long Differerence = GetLocalToGMTDifference() ConvertGMTToLocal = DateAdd("s", Differerence, gmtTime) End Function 'Purpose : Returns the time lDiff between local and GMT (secs). 'Inputs : dtLocalDate The local data time to return as GMT. 'Outputs : Returns the local time in GMT. 'Author : Andrew Baker 'Date : 13/11/2002 10:16 'Notes : A positive number indicates your ahead of GMT. 'Revisions : Public Function GetLocalToGMTDifference() As Long Const TIME_ZONE_ID_INVALID& = &HFFFFFFFF Const TIME_ZONE_ID_STANDARD& = 1 Const TIME_ZONE_ID_UNKNOWN& = 0 Const TIME_ZONE_ID_DAYLIGHT& = 2 Dim tTimeZoneInf As TIME_ZONE_INFORMATION Dim lRet As Long Dim lDiff As Long 'Get time zone info lRet = GetTimeZoneInformation(tTimeZoneInf) 'Convert diff to secs lDiff = -tTimeZoneInf.Bias * 60 GetLocalToGMTDifference = lDiff 'Check if we are in daylight saving time. If lRet = TIME_ZONE_ID_DAYLIGHT& Then 'In daylight savings, apply the bias If tTimeZoneInf.DaylightDate.wMonth <> 0 Then 'if tTimeZoneInf.DaylightDate.wMonth = 0 then the daylight 'saving time change doesn't occur GetLocalToGMTDifference = lDiff - tTimeZoneInf.DaylightBias * 60 End If End If End Function
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