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

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Article ID: 177674 - View products that this article applies to.
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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: July 13, 2004 - Revision: 2.1
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
  • Microsoft Visual Basic 4.0 Standard Edition
  • Microsoft Visual Basic 4.0 Professional Edition
  • Microsoft Visual Basic 4.0 32-Bit Enterprise Edition
Keywords: 
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