/sys$common/syshlp/helplib.hlb CC, Messages, SIZEINCOMPTYP  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Message        <Context> "<type>" is an incomplete type, and so has
                no size.

 Description    A incomplete type has no size and therefore cannot be
                used as the argument to the sizeof operator.

 User Action    Pass a valid type to the sizeof operator.