HOWTO: Toggle the NUM LOCK, CAPS LOCK, and SCROLL LOCK Keys

MORE INFORMATION

To toggle the NUM LOCK, CAPS LOCK, or SCROLL LOCK keys, you can use the following logic:

1. Use the GetKeyboardState function to determine the state of the key.
2. Determine which operating system is being used with the GetVersionEx API. (Windows 95/98/Me and Windows NT/2000 require different methods for toggling these keys.)
3. Under Windows 95, Windows 98, or Windows Me, use the SetKeyboardState API function to set the state of the key. Under Windows NT or Windows 2000, use the keybd_event function to simulate a key press.

This example shows how to toggle these three keys to "on" if they are "off." This sample may be easily modified to toggle them off or just to check their state.

Sample Project

1. Start a new Standard EXE project in Visual Basic. Form1 is created by default.
2. Add a CommandButton to Form1.
3. Add the following code to the General Declarations section of Form1:

         ' Declare Type for API call:
         Private Type OSVERSIONINFO
           dwOSVersionInfoSize As Long
           dwMajorVersion As Long
           dwMinorVersion As Long
           dwBuildNumber As Long
           dwPlatformId As Long
           szCSDVersion As String * 128   '  Maintenance string for PSS usage
         End Type
   
         ' API declarations:
   
         Private Declare Function GetVersionEx Lib "kernel32" _
            Alias "GetVersionExA" _
            (lpVersionInformation As OSVERSIONINFO) As Long
   
         Private Declare Sub keybd_event Lib "user32" _
            (ByVal bVk As Byte, _
             ByVal bScan As Byte, _
             ByVal dwFlags As Long, ByVal dwExtraInfo As Long)
   
         Private Declare Function GetKeyboardState Lib "user32" _
            (pbKeyState As Byte) As Long
   
         Private Declare Function SetKeyboardState Lib "user32" _
            (lppbKeyState As Byte) As Long
   
         ' Constant declarations:
         Const VK_NUMLOCK = &H90
         Const VK_SCROLL = &H91
         Const VK_CAPITAL = &H14
         Const KEYEVENTF_EXTENDEDKEY = &H1
         Const KEYEVENTF_KEYUP = &H2
         Const VER_PLATFORM_WIN32_NT = 2
         Const VER_PLATFORM_WIN32_WINDOWS = 1
   

4. Add the following code to the Click event of the CommandButton:

       Private Sub Command1_Click()
         Dim o As OSVERSIONINFO
         Dim NumLockState As Boolean
         Dim ScrollLockState As Boolean
         Dim CapsLockState As Boolean
   
         o.dwOSVersionInfoSize = Len(o)
         GetVersionEx o
         Dim keys(0 To 255) As Byte
         GetKeyboardState keys(0)
   
         ' NumLock handling:
         NumLockState = keys(VK_NUMLOCK)
         If NumLockState <> True Then    'Turn numlock on
           If o.dwPlatformId = VER_PLATFORM_WIN32_WINDOWS Then  '=== Win95/98
   
             keys(VK_NUMLOCK) = 1
             SetKeyboardState keys(0)
           ElseIf o.dwPlatformId = VER_PLATFORM_WIN32_NT Then   '=== WinNT
           'Simulate Key Press
             keybd_event VK_NUMLOCK, &H45, KEYEVENTF_EXTENDEDKEY Or 0, 0
           'Simulate Key Release
             keybd_event VK_NUMLOCK, &H45, KEYEVENTF_EXTENDEDKEY _
                Or KEYEVENTF_KEYUP, 0
           End If
         End If
   
         ' CapsLock handling:
         CapsLockState = keys(VK_CAPITAL)
         If CapsLockState <> True Then    'Turn capslock on
           If o.dwPlatformId = VER_PLATFORM_WIN32_WINDOWS Then  '=== Win95/98
             keys(VK_CAPITAL) = 1
             SetKeyboardState keys(0)
           ElseIf o.dwPlatformId = VER_PLATFORM_WIN32_NT Then   '=== WinNT
           'Simulate Key Press
             keybd_event VK_CAPITAL, &H45, KEYEVENTF_EXTENDEDKEY Or 0, 0
           'Simulate Key Release
             keybd_event VK_CAPITAL, &H45, KEYEVENTF_EXTENDEDKEY _
                Or KEYEVENTF_KEYUP, 0
           End If
         End If
   
         ' ScrollLock handling:
         ScrollLockState = keys(VK_SCROLL)
         If ScrollLockState <> True Then    'Turn Scroll lock on
           If o.dwPlatformId = VER_PLATFORM_WIN32_WINDOWS Then  '=== Win95/98
             keys(VK_SCROLL) = 1
             SetKeyboardState keys(0)
           ElseIf o.dwPlatformId = VER_PLATFORM_WIN32_NT Then   '=== WinNT
           'Simulate Key Press
             keybd_event VK_SCROLL, &H45, KEYEVENTF_EXTENDEDKEY Or 0, 0
           'Simulate Key Release
             keybd_event VK_SCROLL, &H45, KEYEVENTF_EXTENDEDKEY _
               Or KEYEVENTF_KEYUP, 0
           End If
         End If
       End Sub
   

5. Press the F5 key to run the program. Click the CommandButton. The state of the CAPS LOCK, the NUM LOCK, and the SCROLL LOCK keys should all be "on."