Adding zero in c preprocessor statement

Question

While looking through some c header files (specifically stdarg.h), I noticed a very peculiar line:

#if !defined(__STRICT_ANSI__) || __STDC_VERSI         


        

Answer 1

That avoids a preprocessor syntax error if __STDC_VERSION__ is defined as an empty token (e.g. with #define __STDC_VERSION__).

(Thanks to Jens Gustedt for pointing out that the first version of my answer was wrong.)