Is there a better way to comment the parameters' direction in code?

Question

I want to improve the readability of the code. So I commented the parameter's direction in the code like this:

#define IN
#define OUT

void Add(IN int Para1, IN int Para2, OUT int& Result);

But I think the compiler will replace every instance of IN and OUT with blank and it could be quite a problem some times.

So is there a better way? Thanks.

(I use C++.)

Answer 1

You can try to put it in comments. That is much better and readable.

void Add(/*IN*/ int Para1, /*IN*/ int Para2, /*OUT*/ int& Result);

Answer 2

Yes: Forget those things and use constness. That will work as long as you don't have a "in" and "out" parameter, which is and should be rarely used.

void foo(int i, const std::string& s, std::vector<char>& out_buf);
// i and s are obviously "in" variables, while out_buf could be both, 
// but you can easily show that by giving the parameter a proper name.

Edit: And const correctness does not mean to make value parameters const! This doesn't give the caller any additional information at all, since you can't change his variables either way.