VMS Help CC, Messages, INCOMPDEREF  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Message        <Context> "<expression>" is a pointer to an
                incomplete struct or union and should not be used as
                the left operand of a member dereference.

 Description    In certain modes, Compaq C will allow the struct or
                union specifier of a member dereference operator (->)
                to specify a struct or union that does not contain
                the element specified by the right operand.  While
                this is considered poor programming practice, it was
                common with older C compilers.  In cases where the
                left operand is a pointer to an incomplete type, the
                practice is considered even worse.  While Compaq C
                will accept the construct in certain modes, the code
                should be modified.  Further, this program does not
                conform to the C standard and might not be accepted
                by other C compilers.

 User Action    Be aware of this if you wish to port the program.