Thread: Preprocessor help

Hey!

I'm learning C++ on my own with Practical C++ Programming by Steve Oualline. Pretty good book, but some of the exercises are vague to say the least. I've made it pretty far but the chapter on the preprocessor has proven a real nightmare, so I figure I'd ask for help here.

Exercise 10-1 for example, is "Create a set of macros to define a type called RETURN_STATUS and the following values: RETURN_SUCCESS, RETURN_WARNING, and RETURN_ERROR. Define a macro, CHECK_RETURN_FATAL,,, (sic) that takes a RETURN_STATUS as its argument and returns true if you have a fatal error."

I guess that the person I really should ask is Steve Oualline, but I figure even if I could get in touch with him he has probably forgotten what he meant in the five years since the last edition was published. =)

Anyway, ignoring the fact that I'm not sure I have understood the exercise, my solution would be the preprocessor equivalent of

Code:

if (input == RETURN_ERROR) return true;

But how do I do that? I can't really do conditional logic from within a macro, right?

Thanks in advance for any help you can offer!

simply #define RETURN_ERROR, RETURN_WARNING and RETURN_SUCCESS as 1, <any integer> and 0 as this is common practice. Then typedef (better than #define) RETURN_STATUS as an integral type. Then add a macro called CHECK_RETURN_FATAL that compares its argument to RETURN_ERROR. I can't give you a solution here.

EDIT: You were faster again

Great, thanks guys!

Yeah, Oualline points out repeatedly that the preprocessor is a good way of introducing difficult-to-spot problems. All the more reason to learn how it actually works, I guess =)