7.4.4 Use #ifdef for Explicit 32-bit Versus 64-bit Prototypes

In some cases, specific 32-bit and 64-bit versions of an interface are unavoidable. You can distinguish these by specifying the _LP64 or _ILP32 feature test macros in the headers. Similarly, code that runs in 32-bit and 64-bit environments needs to utilize the appropriate #ifdefs, depending on the compilation mode.