WH_CALLWNDPROC and WH_CALLWNDPROCRET Hooks

The WH_CALLWNDPROC and WH_CALLWNDPROCRET hooks enable you to monitor messages sent to window procedures by the SendMessage function. Windows calls a WH_CALLWNDPROC hook procedure before passing the message to the receiving window procedure, and calls the WH_CALLWNDPROCRET hook procedure after the window procedure has processed the message.

The WH_CALLWNDPROCRET hook passes the address of a CWPRETSTRUCT structure to the hook procedure. The structure contains the return value from the window procedure that processed the message, as well as the message parameters associated with the message. Subclassing the window does not work for messages set between processes.

For more information, see the CallWndProc and CallWndRetProc functions.