KeyboardProc callback function
An application-defined or library-defined callback function used with the SetWindowsHookEx function. The system calls this function whenever an application calls the GetMessage or PeekMessage function and there is a keyboard message (WM_KEYUP or WM_KEYDOWN) to be processed.
The HOOKPROC type defines a pointer to this callback function. KeyboardProc is a placeholder for the application-defined or library-defined function name.
LRESULT CALLBACK KeyboardProc( _In_ int code, _In_ WPARAM wParam, _In_ LPARAM lParam );
A code the hook procedure uses to determine how to process the message. If code is less than zero, the hook procedure must pass the message to the CallNextHookEx function without further processing and should return the value returned by CallNextHookEx. This parameter can be one of the following values.
Value Meaning HC_ACTION 0
The wParam and lParam parameters contain information about a keystroke message.
The wParam and lParam parameters contain information about a keystroke message, and the keystroke message has not been removed from the message queue. (An application called the PeekMessage function, specifying the PM_NOREMOVE flag.)
The virtual-key code of the key that generated the keystroke message.
The repeat count, scan code, extended-key flag, context code, previous key-state flag, and transition-state flag. For more information about the lParam parameter, see Keystroke Message Flags. The following table describes the bits of this value.
Bits Description 0-15 The repeat count. The value is the number of times the keystroke is repeated as a result of the user's holding down the key. 16-23 The scan code. The value depends on the OEM. 24 Indicates whether the key is an extended key, such as a function key or a key on the numeric keypad. The value is 1 if the key is an extended key; otherwise, it is 0. 25-28 Reserved. 29 The context code. The value is 1 if the ALT key is down; otherwise, it is 0. 30 The previous key state. The value is 1 if the key is down before the message is sent; it is 0 if the key is up. 31 The transition state. The value is 0 if the key is being pressed and 1 if it is being released.
If code is less than zero, the hook procedure must return the value returned by CallNextHookEx.
If code is greater than or equal to zero, and the hook procedure did not process the message, it is highly recommended that you call CallNextHookEx and return the value it returns; otherwise, other applications that have installed WH_KEYBOARD hooks will not receive hook notifications and may behave incorrectly as a result. If the hook procedure processed the message, it may return a nonzero value to prevent the system from passing the message to the rest of the hook chain or the target window procedure.
This hook may be called in the context of the thread that installed it. The call is made by sending a message to the thread that installed the hook. Therefore, the thread that installed the hook must have a message loop.
Minimum supported client
Windows 2000 Professional [desktop apps only]
Minimum supported server
Windows 2000 Server [desktop apps only]
|Winuser.h (include Windows.h)|