How To Toggle the NUM LOCK, CAPS LOCK, and SCROLL LOCK Keys

Summary

This article demonstrates how to toggle the NUM LOCK, CAPS LOCK, AND SCROLL LOCK keys under Windows 95, Windows 98, Windows Me, Windows NT, or Windows 2000.

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."

References

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

127190 : How To Toggle the NUM LOCK, CAPS LOCK, and SCROLL LOCK Keys

Properties

Article ID: 177674 - Last Review: Jul 13, 2004 - Revision: 1

Feedback