BlockInput function

Blocks keyboard and mouse input events from reaching applications.

Syntax

BOOL BlockInput(
  BOOL fBlockIt
);

Parameters

fBlockIt

Type: BOOL

The function's purpose. If this parameter is TRUE, keyboard and mouse input events are blocked. If this parameter is FALSE, keyboard and mouse events are unblocked. Note that only the thread that blocked input can successfully unblock input.

Return Value

Type: BOOL

If the function succeeds, the return value is nonzero.

If input is already blocked, the return value is zero. To get extended error information, call GetLastError.

Remarks

When input is blocked, real physical input from the mouse or keyboard will not affect the input queue's synchronous key state (reported by GetKeyState and GetKeyboardState), nor will it affect the asynchronous key state (reported by GetAsyncKeyState). However, the thread that is blocking input can affect both of these key states by calling SendInput. No other thread can do this.

The system will unblock input in the following cases:

  • The thread that blocked input unexpectedly exits without calling BlockInput with fBlock set to FALSE. In this case, the system cleans up properly and re-enables input.
  • The user presses CTRL+ALT+DEL or the system invokes the Hard System Error modal message box (for example, when a program faults or a device fails).

Requirements

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

See Also

Conceptual

GetAsyncKeyState

GetKeyState

GetKeyboardState

Keyboard Input

Reference

SendInput