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

 Message        <Context> "<expression>" of type "<type>", is being
                converted to "<target type>".  Such a cast is not
                permitted by the standard.

 Description    The standard only permits casts from a pointer to an
                object incomplete type to another pointer to an
                object or incomplete type, or from a pointer to
                function type to another pointer to function type.
                Note that void is considered an incomplete type, so
                casts between pointer to void and pointer to function
                types are not permitted by the C standard.

 User Action    Be aware of this difference if you plan to port this
                source to another compiler.