[c++] What is the worst real-world macros/pre-processor abuse you've ever come across?

Another piece of 'creative' use of the preprocessor, though it is more in the terminology employed than in the mechanics (which are incredibly mundane):

/***********************************************************************
 * OS2 and PCDOS share a lot of common codes.  However, sometimes
 * OS2 needs codes similar to those of UNIX.  NOTPCDOS is used in these
 * situations
 */

#ifdef OS2
#define PCDOS
#define NOTPCDOS
#else /* OS2 */
#ifndef PCDOS
#define NOTPCDOS
#endif /* PCDOS */
#endif /* OS2 */

Genuine code - I thought I'd removed it, but apparently not. I must have done so out in some temporary branch and not gotten permission to check it back into the main code. One more item for the 'to do' list.

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