Macro `__unix__` not defined in MacOS X

Question

I noticed that in MacOS X (Lion), the macro __unix__ is not defined. Since MacOS has its roots in BSD UNIX, shouldn't that be the case?

Is it possible to let the compiler/preprocessor know that I want it to be considered a UNIX system?

Answer 1

The predefined macros site suggests using:

#if defined(unix) || defined(__unix__) || defined(__unix)
# define PREDEF_PLATFORM_UNIX
#endif

To distinguish UNIX systems. They also have warning notes about a number of compilers that don't set any of these. Depending on why you care about what the platform is you might be better off looking at configure time (in configure.ac or whatever build system you're using).

Answer 2

I think this site gives the most comprehensive answer.

In short, to include Apple platforms and common Unix platforms, you'll need:

#if defined(__unix__) || defined(__unix) || \
        (defined(__APPLE__) && defined(__MACH__))
...
#endif