The BN_CLICKED notification message is sent when the user clicks a button. The parent window of the button receives this notification message through the WM_COMMAND message.
BN_CLICKED
idButton = (int) LOWORD(wParam); // identifier of button
hwndButton = (HWND) lParam; // handle to button
A disabled button does not send a BN_CLICKED notification message to its parent window.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Buttons Overview, Button Messages, WM_COMMAND