Interfacing with C libs: weeding through C/C++ macros and such in header files

[Alec Stewart]

Hello all!

So while I have a decent grasp on D, I've been having trouble 
figuring out specific projects that I could do in D, so I thought 
I'd maybe find a little C or C++ library I could transfer over to 
D. I decided to make my life easier and look for something that's 
just a single header file, and while that does make things easier 
there are a TON of macros and inline functions that it almost 
seems ridiculous and it's somewhat overwhelming.

Example without code; for some reason a macro is defined for the 
stdlib functions `malloc`, `realloc`, and `free`. Maybe it's just 
because I don't have any pro experience with C or C++, but that 
seems a bit excessive. Or I could just be dumb.

Example with code (because I need help figuring out how whether I 
even need this or not):

     #ifndef RS_API
     #ifdef RS_NOINLINE
     /* GCC version 3.1 required for the no inline attribute. */
     #if RS_GCC_VERSION > 30100
     #define RS_API static __attribute__((noinline))
     #elif defined(_MSC_VER)
     #define RS_API static __declspec(noinline)
     #else
     #define RS_API static
     #endif
     #elif RS_C99
     #define RS_API static inline
     #elif defined(__GNUC__)
     #define RS_API static __inline__
     #elif defined(_MSC_VER)
     #define RS_API static __forceinline
     #else
     #define RS_API static
     #endif
     #endif

I understand what it's doing, but do I really any of this with D? 
And then there's this inline function

     #define RS_DATA_SIZE(f, s, input)                             
           \
	    do {                                                         
    \
		    if (rs_is_heap(input))                                  \
			    f(s, input->heap.buffer, rs_heap_len(input));   \
		    else                                                    \
			    f(s, input->stack.buffer, rs_stack_len(input)); \
	    } while (0)

so yea. There's a little over 300 lines of preprocessor stuff. My 
question is how you all determine what to carry over from C libs 
in terms of preprocessor stuff. I imagine most useful values 
everyone just makes an enum for, and structs and unions are kept.

Thanks for any help you give!