Thread: #define - something I need to understand

Hi all,
I've been programming in C language for a while now, years to be realistic.
I was looking at this file today, and I came across something that is (as an assumption) extremely easy, but for the life of me I am not able to understand it.

#define _FAR

#define _PTR_ _FAR *


then the code goes on defining pointers to integers, etc...

Throughout the years I've programmed in C, I was used to something like this:

#define _SOMETHING 1
#define _SOMETHING2 _SOMETHING

which makes sense to me. I have an identifier and a string-token.

Even saying something as
#define _SOMETHING3

is acceptable to me because the way I've used it is as a check
#if defined _SOMETHING3
or #ifndef _SOMETHING3


My question is, how am I able to use _FAR when I do not have an actual string-token associated with it? Can someone explain to me what these two lines mean?
#define _FAR
#define _PTR_ _FAR *

Thanks in advance!

_FAR is nothing...

_PTR_ _FAR * is a pointer to nothing... essentially just a *

They could have just as easily done #define _PTR_ *

int _PTR_ x; amounts to int *x;

The first define works for Turbo C FAR pointers, and I suspect the second line works for another compiler from those days - no clue which one, though.

They do look weird, but don't let them rattle you, they are still the same simple token replacement and definition tool, you thought they were.

CommonTater, Adak & Salem,
thanks a lot!
Makes sense now...

Originally Posted by Salem

The first one would have been better written as

#define _FAR /* raise the dead - the zombie walks again! */

If you see "far" in your code, then you're looking at 20 to 30 year old 16-bit DOS code.

Macros like this are typically used to remove ancient compiler specific keywords so that the code will compile (to a fashion) on new compilers.

Thanks Salem.... I had fogotten all about that!