Home > How-To Library > Date & Time

How to get GMT time from local system time

****************************************************************
*       © 2007 CodeItBetter http://www.codeitbetter.com        *
*          This notice MUST stay intact for legal use          *
****************************************************************

Option Explicit

Private Const TIME_ZONE_ID_DAYLIGHT As Long = 2
Private Const VER_PLATFORM_WIN32_NT = 2

Private Const HKEY_LOCAL_MACHINE = &H80000002
Private Const KEY_ENUMERATE_SUB_KEYS As Long = &H8
Private Const KEY_NOTIFY As Long = &H10
Private Const KEY_QUERY_VALUE As Long = &H1
Private Const REG_BINARY = 3
Private Const REG_DWORD As Long = 4
Private Const REG_SZ As Long = 1
Private Const STANDARD_RIGHTS_READ As Long = &H20000
Private Const SYNCHRONIZE As Long = &H100000
Private Const KEY_READ As Long = ((STANDARD_RIGHTS_READ Or KEY_QUERY_VALUE Or _
    KEY_ENUMERATE_SUB_KEYS Or KEY_NOTIFY) And (Not SYNCHRONIZE))

Private Type OSVERSIONINFO
    OSVSize As Long
    dwVerMajor As Long
    dwVerMinor As Long
    dwBuildNumber As Long
    PlatformID As Long
    szCSDVersion As String * 128
End Type

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 REG_TIME_ZONE_INFORMATION
    Bias As Long
    StandardBias As Long
    DaylightBias As Long
    StandardDate As SYSTEMTIME
    DaylightDate As SYSTEMTIME
End Type

Private Type TIME_ZONE_INFORMATION
    Bias As Long
    StandardName(63) As Byte
    StandardDate As SYSTEMTIME
    StandardBias As Long
    DaylightName(63) As Byte
    DaylightDate As SYSTEMTIME
    DaylightBias As Long
End Type

Declare Sub GetLocalTime Lib "kernel32" (lpSystemTime As SYSTEMTIME)
Declare Sub GetSystemTime Lib "kernel32" (lpSystemTime As SYSTEMTIME)
Declare Function GetTimeZoneInformation Lib "kernel32" _
    (lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long
Declare Function GetVersionEx Lib "kernel32" Alias "GetVersionExA" _
    (lpVersionInformation As OSVERSIONINFO) As Long
Declare Function RegCloseKey Lib "advapi32.dll" (ByVal hKey As Long) As Long
Declare Function RegOpenKeyEx Lib "advapi32.dll" Alias "RegOpenKeyExA" _
    (ByVal hKey As Long, ByVal lpsSubKey As String, ByVal ulOptions As Long, _
    ByVal samDesired As Long, phkResult As Long) As Long
Declare Function RegQueryValueEx Lib "advapi32.dll" Alias "RegQueryValueExA" _
    (ByVal hKey As Long, ByVal lpszValueName As String, ByVal lpdwReserved As Long, _
    lpdwType As Long, lpData As Any, lpcbData As Long) As Long

Public Function IsDST() As Boolean
    Dim udtTimezoneInfo As TIME_ZONE_INFORMATION
    IsDST = (GetTimeZoneInformation(udtTimezoneInfo) = TIME_ZONE_ID_DAYLIGHT)
End Function

Public Function IsWinNT() As Boolean
    Dim udtVersion As OSVERSIONINFO
    ' initialize UDT
    udtVersion.OSVSize = Len(udtVersion)
    ' try get the data
    If GetVersionEx(udtVersion) <> 1 Then Exit Function
    ' check for information
    IsWinNT = (udtVersion.PlatformID = VER_PLATFORM_WIN32_NT)
End Function

Public Function NowGMT() As Date
    Dim udtSysTime As SYSTEMTIME, udtRegTZInfo As REG_TIME_ZONE_INFORMATION
    Dim lngKey As Long, strTimezone, lngBias As Long
    If IsWinNT Then
        strTimezone = "SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones\GMT Standard Time"
    Else
        strTimezone = "SOFTWARE\Microsoft\Windows\CurrentVersion\Time Zones\GMT Standard Time"
    End If
    If RegOpenKeyEx(HKEY_LOCAL_MACHINE, strTimezone, 0, KEY_READ, lngKey) = 0 Then
        If RegQueryValueEx(lngKey, "TZI", 0&, ByVal 0&, udtRegTZInfo, Len(udtRegTZInfo)) = 0 Then
            If IsDST Then
                lngBias = udtRegTZInfo.DaylightBias
            Else
                lngBias = udtRegTZInfo.StandardBias
            End If
        End If
        RegCloseKey lngKey
    End If
    GetSystemTime udtSysTime
    With udtSysTime
        NowGMT = DateSerial(.wYear, .wMonth, .wDay) + _
            TimeSerial(.wHour, .wMinute - lngBias, .wSecond)
    End With
End Function

If you would like to submit your code here please us. Do not forget to mention your name. We are always thankful to each and everyone of you who submitted their code here.