Description

   The _toupper macro is equivalent to the toupper function except
   that its argument must be a lowercase letter (not uppercase, not
   EOF).

   As of OpenVMS Version 8.3 and to comply with the C99 ANSI
   standard and X/Open Specification, the _toupper macro by default
   does not evaluate parameters more than once. It simply calls
   the toupper function. This avoids side effects (such as i++
   or function calls) where the user can tell how many times an
   expression is evaluated.

   To keep the older, optimized _toupper macro behavior, compile
   with /DEFINE=_FAST_TOUPPER. Then, as in previous releases, _
   toupper optimizes the call to avoid the overhead of a runtime
   call. The parameters are checked to determine how to calculate
   the result, thereby creating unwanted side effects. So when
   compiling with /DEFINE=_FAST_TOUPPER, do not use the _toupper
   macro with arguments that contain side-effect operations. For
   instance, the following example will not return the expected
   result:

   d = _toupper (c++);