The SysMsgProc hook procedure is a library-defined callback function the system calls after an input event occurs in a dialog box, message box, menu, or scroll bar, but before the message generated by the input event is processed. The hook procedure can monitor messages for any dialog box, message box, menu, or scroll bar in the system.
LRESULT CALLBACK SysMsgProc(
| int nCode, | // message flag |
| WPARAM wParam, | // undefined |
| LPARAM lParam | // address of structure with message data |
| ); |
Parameters
nCode
Specifies the type of input event that generated the message. This parameter can be one of the following values:
| Value | Meaning |
| MSGF_DIALOGBOX | The input event occurred in a message box or dialog box. |
| MSGF_MENU | The input event occurred in a menu. |
| MSGF_SCROLLBAR | The input event occurred in a scroll bar. |
| MSGF_NEXTWINDOW | The input event occurred as a result of the user's pressing the ALT+TAB key combination to activate a different window. |
If nCode 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.
wParam
Specifies a NULL value.
lParam
Points to an MSG message structure.
Return Values
If the hook procedure processes the message, the return value must be nonzero. Otherwise, it must be zero.
Remarks
An application installs the hook procedure by specifying the WH_SYSMSGFILTER hook type and the address of the hook procedure in a call to the SetWindowsHookEx function.
SysMsgProc is a placeholder for the library-defined function name.
See Also