Re: macro expansion and types in <sys/types.h>

[Alan Barrett <apb%cequrux.com@localhost>]

On Thu, 04 Sep 2014, Brook Milligan wrote:
> #ifndef uint16_t
> typedef __uint16_t      uint16_t;
> #define uint16_t        __uint16_t
> #endif

It's allowed for a macro to be #define'd as itself[*].  Then testing it
with #ifdef works, but expanding it doesn't change anything.

So, we could rewrite the above code as follows:

        #ifndef uint16_t
        typedef __uint16_t uint16_t;
        #define uint16_t   uint16_t
        #endif

[*] ISO C99 section 6.10.3.4 [...] If the name of the macro 
being replaced is found during this scan of the replacement 
list [...], it is not replaced. Furthermore, if any nested 
replacements encounter the name of the macro being replaced, 
it is not replaced.

--apb (Alan Barrett)