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

 Message        <Context> "<type>" has function or void type and may
                not appear in this context.  The compiler will treat
                the type as if it were char.

 Description    A function or void type cannot be used as the
                argument of the sizeof operator or the
                __builtin_alignof builtin.  For compatibility with
                some other compilers, an output file is still
                created.  The result produced will be the same as if
                a char type was passed.  This may or may not be
                compatible with other compilers that accept this
                syntax.

 User Action    Pass a valid type to the operator or builtin.