How to change time zone information by using Visual Basic

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Article ID: 221542 - View products that this article applies to.
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SUMMARY

It is sometimes necessary to programmatically change the time zone for the system where the application is running. This article demonstrates this technique.

MORE INFORMATION

The way to implement this effect is as follows:
  1. Determine which time zone you would like to change to.
  2. Find the key in the registry that contains the information needed to fill the TIME_ZONE_INFORMATION structure.
  3. Read in that information and load the values into a variable of type TIME_ZONE_INFORMATION.
  4. Call the SetTimeZoneInformation API, passing it the TIME_ZONE_INFORMATION struct variable.
The location in the registry that contains time zone information differs between Windows 9x and Windows NT/Windows 2000.

For Windows NT and Windows 2000, it is located at:
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones
For Windows 9x, it is located at:
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Time Zones
The Time Zone key names differ between Windows NT, Windows 2000, and Windows 9x as well because Windows NT and Windows 2000 append the string "Standard Time" to the different keys whereas Windows 9x does not.

For example:

In Windows NT and Windows 2000, you would see this key:
Pacific Standard Time
while in Windows 9x, you would see this key:
Pacific
The registry location where the current Date/Time settings can be found is:
HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation

Step-by-step example

The code sample below requires a form with a listbox. The listbox is loaded with the possible time zone values that the user can select with a double-click to change the time zone. It will show a messagebox that, once dismissed, will change the system settings back to their original values.
  1. Create a new Standard EXE project. Form1 is created by default.
  2. Add a Listbox control to Form1.
  3. Add the following code to the General Declarations section of Form1:
    Option Explicit
    
    ' Operating System version information declares
    
    Private Const VER_PLATFORM_WIN32_NT = 2
    Private Const VER_PLATFORM_WIN32_WINDOWS = 1
    
    Private Type OSVERSIONINFO
            dwOSVersionInfoSize As Long
            dwMajorVersion As Long
            dwMinorVersion As Long
            dwBuildNumber As Long
            dwPlatformId As Long
            szCSDVersion As String * 128 ' Maintenance string
    End Type
    
    Private Declare Function GetVersionEx Lib "kernel32" _
    Alias "GetVersionExA" (lpVersionInformation As OSVERSIONINFO) As Long
    
    ' Time Zone information declares
    
    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 REGTIMEZONEINFORMATION
       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(0 To 63) As Byte ' used to accommodate Unicode strings
       StandardDate As SYSTEMTIME
       StandardBias As Long
       DaylightName(0 To 63) As Byte ' used to accommodate Unicode strings
       DaylightDate As SYSTEMTIME
       DaylightBias As Long
    End Type
    
    Private Const TIME_ZONE_ID_INVALID = &HFFFFFFFF
    Private Const TIME_ZONE_ID_UNKNOWN = 0
    Private Const TIME_ZONE_ID_STANDARD = 1
    Private Const TIME_ZONE_ID_DAYLIGHT = 2
    
    Private Declare Function GetTimeZoneInformation Lib "kernel32" _
    (lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long
    
    Private Declare Function SetTimeZoneInformation Lib "kernel32" _
    (lpTimeZoneInformation As TIME_ZONE_INFORMATION) As Long
    
    ' Registry information declares
    Private Const REG_SZ As Long = 1
    Private Const REG_BINARY = 3
    Private Const REG_DWORD As Long = 4
    
    Private Const HKEY_CLASSES_ROOT = &H80000000
    Private Const HKEY_CURRENT_USER = &H80000001
    Private Const HKEY_LOCAL_MACHINE = &H80000002
    Private Const HKEY_USERS = &H80000003
    
    Private Const ERROR_SUCCESS = 0
    Private Const ERROR_BADDB = 1
    Private Const ERROR_BADKEY = 2
    Private Const ERROR_CANTOPEN = 3
    Private Const ERROR_CANTREAD = 4
    Private Const ERROR_CANTWRITE = 5
    Private Const ERROR_OUTOFMEMORY = 6
    Private Const ERROR_ARENA_TRASHED = 7
    Private Const ERROR_ACCESS_DENIED = 8
    Private Const ERROR_INVALID_PARAMETERS = 87
    Private Const ERROR_NO_MORE_ITEMS = 259
    
    Private Const KEY_ALL_ACCESS = &H3F
    
    Private Const REG_OPTION_NON_VOLATILE = 0
    
    Private Declare Function RegOpenKeyEx Lib "advapi32.dll" _
       Alias "RegOpenKeyExA" ( _
       ByVal hKey As Long, _
       ByVal lpSubKey As String, _
       ByVal ulOptions As Long, _
       ByVal samDesired As Long, _
       phkResult As Long) _
    As Long
    
    Private 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
    
    Private Declare Function RegQueryValueExString Lib "advapi32.dll" _
       Alias "RegQueryValueExA" ( _
       ByVal hKey As Long, _
       ByVal lpValueName As String, _
       ByVal lpReserved As Long, _
       lpType As Long, _
       ByVal lpData As String, _
       lpcbData As Long) _
    As Long
    
    Private Declare Function RegEnumKey Lib "advapi32.dll" _
       Alias "RegEnumKeyA" ( _
       ByVal hKey As Long, _
       ByVal dwIndex As Long, _
       ByVal lpName As String, _
       ByVal cbName As Long) _
    As Long
    
    Private Declare Function RegCloseKey Lib "advapi32.dll" ( _
       ByVal hKey As Long) _
    As Long
    
    ' Registry Constants
    Const SKEY_NT = "SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones"
    Const SKEY_9X = "SOFTWARE\Microsoft\Windows\CurrentVersion\Time Zones"
    
    ' The following declaration is different from the one in the API viewer.
    ' To disable implicit ANSI<->Unicode conversion, it changes the 
    ' variable types of lpMultiByteStr and lpWideCharStr to Any.
    '
    Private Declare Function MultiByteToWideChar Lib "kernel32" ( _
        ByVal CodePage As Long, _
        ByVal dwFlags As Long, _
        lpMultiByteStr As Any, _
        ByVal cchMultiByte As Long, _
        lpWideCharStr As Any, _
        ByVal cchWideChar As Long) As Long
        
    ' The above Declare and the following Constants are used to make
    ' this sample compatible with Double Byte Character Systems (DBCS).
    Private Const CP_ACP = 0
    Private Const MB_PRECOMPOSED = &H1
    Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" ( _ 
    ByRef Destination As Any, _
    ByRef Source As Any, _
    ByVal numbytes As Long)
    Dim SubKey As String
    
    Private Sub Form_Load()
       Dim lRetVal As Long, lResult As Long, lCurIdx As Long
       Dim lDataLen As Long, lValueLen As Long, hKeyResult As Long
       Dim strvalue As String
       Dim osV As OSVERSIONINFO
    
    ' Win9x and WinNT have a slightly different registry structure. Determine
    ' the operating system and set a module variable to the correct subkey.
    
       osV.dwOSVersionInfoSize = Len(osV)
       Call GetVersionEx(osV)
       If osV.dwPlatformId = VER_PLATFORM_WIN32_NT Then
          SubKey = SKEY_NT
       Else
          SubKey = SKEY_9X
       End If
    
       lRetVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, SubKey, 0, _
                              KEY_ALL_ACCESS, hKeyResult)
    
       If lRetVal = ERROR_SUCCESS Then
    
          lCurIdx = 0
          lDataLen = 32
          lValueLen = 32
    
          Do
             strvalue = String(lValueLen, 0)
             lResult = RegEnumKey(hKeyResult, lCurIdx, strvalue, lDataLen)
    
             If lResult = ERROR_SUCCESS Then
                List1.AddItem Left(strvalue, lValueLen)
             End If
    
             lCurIdx = lCurIdx + 1
    
          Loop While lResult = ERROR_SUCCESS
    
          RegCloseKey hKeyResult
       Else
          List1.AddItem "Could not open registry key"
       End If
    End Sub
    
    Private Sub List1_DblClick()
       Dim TZ As TIME_ZONE_INFORMATION, oldTZ As TIME_ZONE_INFORMATION
       Dim rTZI As REGTIMEZONEINFORMATION
       Dim bytDLTName(32) As Byte, bytSTDName(32) As Byte
       Dim cbStr As Long, dwType As Long
       Dim lRetVal As Long, hKeyResult As Long, lngData As Long
    
       lRetVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, SubKey & "\" & List1.Text, _
                               0, KEY_ALL_ACCESS, hKeyResult)
    
       If lRetVal = ERROR_SUCCESS Then
          lRetVal = RegQueryValueEx(hKeyResult, "TZI", 0&, ByVal 0&, _
                                      rTZI, Len(rTZI))
    
          If lRetVal = ERROR_SUCCESS Then
             TZ.Bias = rTZI.Bias
             TZ.StandardBias = rTZI.StandardBias
             TZ.DaylightBias = rTZI.DaylightBias
             TZ.StandardDate = rTZI.StandardDate
             TZ.DaylightDate = rTZI.DaylightDate
    
             cbStr = 32
             dwType = REG_SZ
    
             lRetVal = RegQueryValueEx(hKeyResult, "Std", _
                         0&, dwType, bytSTDName(0), cbStr)
    
             If lRetVal = ERROR_SUCCESS Then
                Call MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, _
                   bytSTDName(0), cbStr, TZ.StandardName(0), 32)
             Else
                RegCloseKey hKeyResult
                Exit Sub
             End If
    
             cbStr = 32
             dwType = REG_SZ
    
             lRetVal = RegQueryValueEx(hKeyResult, "Dlt", _
                         0&, dwType, bytDLTName(0), cbStr)
    
             If lRetVal = ERROR_SUCCESS Then
                Call MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, _
                   bytDLTName(0), cbStr, TZ.DaylightName(0), 32)
             Else
                RegCloseKey hKeyResult
                Exit Sub
             End If
    
             lRetVal = GetTimeZoneInformation(oldTZ)
    
             If lRetVal = TIME_ZONE_ID_INVALID Then
                MsgBox "Error getting original TimeZone Info"
                RegCloseKey hKeyResult
                Exit Sub
             Else
             If TZ.DaylightDate.wMonth <> 0 And TZ.DaylightBias <> 0 Then
                lRetVal = SetTimeZoneInformation(TZ)
             Else
               Call CopyMemory(TZ.DaylightName(0), TZ.StandardName(0), 64)
               TZ.DaylightBias = 0
               lRetVal = SetTimeZoneInformation(TZ)
             End If
                MsgBox "Time Zone Changed, Click OK to restore"
                lRetVal = SetTimeZoneInformation(oldTZ)
             End If
          End If
    
          RegCloseKey hKeyResult
       End If
    End Sub
    					
  4. Run the program, and note that the listbox displays all of the available time zones.
  5. Select a time zone, and then double-click it. Your system locale is changed to the selected zone. You receive the following message:
    Time Zone Changed, Click OK to restore
  6. In Control Panel, double-click the Date/Time icon. You can also reach this dialog by double-clicking the clock in the system tray. Click the Time Zone tab and observe that the time zone has been changed.
  7. Close the Date/Time Properties dialog box and click OK on the message box displayed by your application. Repeat the previous step to confirm that the time zone information has been restored.

Properties

Article ID: 221542 - Last Review: November 8, 2004 - Revision: 3.1
APPLIES TO
  • Microsoft Visual Basic 5.0 Learning Edition
  • Microsoft Visual Basic 6.0 Learning Edition
  • Microsoft Visual Basic 5.0 Professional Edition
  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition
Keywords: 
kbhowto kbapi KB221542

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