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

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 5.0
• Microsoft Visual Basic Standard, Professional, and Enterprise Editions, 32-bit only, for Windows, version 4.0

SUMMARY

This article demonstrates how to toggle the NUM LOCK, CAPS LOCK, AND SCROLL LOCK keys under both Windows 95 and Windows NT.

MORE INFORMATION

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

- Use the GetKeyboardState function to determine the state of the key.

- Determine which operating system is being used with the GetVersionEx API.

  (Windows 95 and Windows NT require different methods for toggling these
  keys.)

  of the key. Under Windows NT, use the keybd_event function to simulate a
  key press.

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
               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
               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
               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."

REFERENCES

For additional information, please see the following articles in the Microsoft Knowledge Base:

   ARTICLE-ID: Q127190
   TITLE     : HOWTO: Toggle the NUM LOCK, CAPS LOCK, and SCROLL LOCK Keys