ppropriate
       structure type to obtain further information about the event.
       The <TT
CLASS="PARAMETER"
>passThrough</TT
> parameter is the pointer
       provided to <CODE
CLASS="FUNCTION"
>PQregisterEventProc</CODE
> when the event
       procedure was registered.  The function should return a non-zero value
       if it succeeds and zero if it fails.
      </P
><P
>       A particular event procedure can be registered only once in any
       <TT
CLASS="STRUCTNAME"
>PGconn</TT
>.  This is because