/UNDEFINE

    /UNDEFINE=(identifier[,...])
    /NOUNDEFINE (D)

 Performs the same function as the #undef preprocessor directive:
 it cancels a macro definition.

 The /UNDEFINE qualifier is useful for undefining the predefined VSI
 C preprocessor constants.  For example, if you use a preprocessor
 constant (such as vaxc, VAXC, VAX11C, or vms) to conditionally
 compile segments of code specific to VSI C for OpenVMS Systems, you
 can undefine constants to see how the portable sections of your
 program execute.  For example:

 /UNDEFINE="vaxc"

 When both /DEFINE and /UNDEFINE are present on the CC command line,
 /DEFINE is evaluated before /UNDEFINE.

 The default is /NOUNDEFINE.