VMS Help CC, Messages, LONGDOUBLENY1  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Message        <Context> type long double has the same
                representation as type double on this platform and is
                treated as a synonym for type double in this
                compilation mode.

 Description    Compaq C does not support the long double type on
                this platform.  In this compilation mode, the
                compiler will treat the long double type as a synonym
                for the double type.

 User Action    Be aware of this.