Chapter 9. WH_CALLWNDPROC
The WH_CALLWNDPROC hook intercepts messages that
you send through the SendMessage application
programming interface (API) function. This
hook can view messages, but it cannot
modify or discard them. Normally, filter functions discard messages
by not calling the CallNextHookEx function and
returning a zero. But in the case of the
WH_CALLWNDPROC hook, after the filter function is
finished processing the message, it
returns control to the SendMessage function,
which then proceeds to send the message. For this reason, it is not
possible to discard the sent message.
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