Yes, Plan 9 c has its own C library which does not follow ANSI/ISO though it is very similar to ISO C. Its syntax is pretty much c89 and the useful bits of c99.

Yes, Plan 9 c has its own C library which does not follow ANSI/ISO though it is very similar to ISO C. Its syntax is pretty much c89 and the useful bits of c99. To build ANSI/POSIX you use the APE (ANSI/POSIX Environment) compilers and libraries which are built in. It's only reason for existing is to help with porting Unix baggage. The compiler is kencc which is why it is different. Plan 9 also still uses a.out for binary images.