The C compiler that comes with A/UX is NOT compatible with the draft ANSI
standard for C. (The A/UX C compiler is the standard System 5.2.2 release
compiler.)
Under the Macintosh OS, the MPW 3.0 C compiler was written to move towards the
ANSI draft standard, but since the standard is at a draft stage, engineering
has a moving target.
However, if you read Appendix D of the MPW 3.0 C reference manual (APDA
#M0022LL/A) you will see that the majority of the changes to the C compiler
were implemented for ANSI compatibility.
Both Appendix D and the Release Notes have sections pertinent to ANSI
compatibility. Read them for further information.