keybd_event function (winuser.h)

Article
02/22/2024

Synthesizes a keystroke. The system can use such a synthesized keystroke to generate a WM_KEYUP or WM_KEYDOWN message. The keyboard driver's interrupt handler calls the keybd_event function.

Note This function has been superseded. Use SendInput instead.

Syntax

void keybd_event(
  [in] BYTE      bVk,
  [in] BYTE      bScan,
  [in] DWORD     dwFlags,
  [in] ULONG_PTR dwExtraInfo
);

Parameters

[in] bVk

Type: BYTE

A virtual-key code. The code must be a value in the range 1 to 254. For a complete list, see Virtual Key Codes.

[in] bScan

Type: BYTE

A hardware scan code for the key.

[in] dwFlags

Type: DWORD

Controls various aspects of function operation. This parameter can be one or more of the following values.

Value	Meaning
KEYEVENTF_EXTENDEDKEY 0x0001	If specified, the scan code was preceded by a prefix byte having the value 0xE0 (224).
KEYEVENTF_KEYUP 0x0002	If specified, the key is being released. If not specified, the key is being depressed.

[in] dwExtraInfo

Type: ULONG_PTR

An additional value associated with the key stroke.

Return value

None

Remarks

An application can simulate a press of the PRINTSCRN key in order to obtain a screen snapshot and save it to the clipboard. To do this, call keybd_event with the bVk parameter set to VK_SNAPSHOT.

Examples

The following sample program toggles the NUM LOCK light by using keybd_event with a virtual key of VK_NUMLOCK. It takes a Boolean value that indicates whether the light should be turned off (FALSE) or on (TRUE). The same technique can be used for the CAPS LOCK key (VK_CAPITAL) and the SCROLL LOCK key (VK_SCROLL).


   #include <windows.h>

   void SetNumLock( BOOL bState )
   {
      BYTE keyState[256];

      GetKeyboardState((LPBYTE)&keyState);
      if( (bState && !(keyState[VK_NUMLOCK] & 1)) ||
          (!bState && (keyState[VK_NUMLOCK] & 1)) )
      {
      // Simulate a key press
         keybd_event( VK_NUMLOCK,
                      0x45,
                      KEYEVENTF_EXTENDEDKEY | 0,
                      0 );

      // Simulate a key release
         keybd_event( VK_NUMLOCK,
                      0x45,
                      KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP,
                      0);
      }
   }

   void main()
   {
      SetNumLock( TRUE );
   }

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	winuser.h (include Windows.h)
Library	User32.lib
DLL	User32.dll

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