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

 Message        <Context> the expression "<expr>" modifies "<var>",
                and fetches its value in a computation that is not
                used to produce the modified value without an
                intervening sequence point.  This behavior is
                undefined.

 Description    The compiler has detected a case where the same
                variable has been modified and fetched in a
                computation that does not later modify that same
                variable.  Because the order of the variable fetch
                and store is not defined, this expression might
                produce different results on different platforms.

 User Action    Rewrite the expression so that if a variable is
                stored to, it is fetched only to determine the value
                to be stored.