Using the function of a specific library

Question

I have a problem: I would like to use the function abs of the library complex.

However, I undergo an error warning me the function abs used is #define abs(x) (x > 0) ? x : -(x).

Thus, I think the problem comes from my imports. Because of I also include the stdio and stdlib libraries, the compiler may use the function abs defined in one of these libraries.

So my question is: how can I use the function abs of the library complex without removing any import ?

Thanks a lot in advance for your response.

Answer 1

Wrap parens around it.

(abs)(whatever);

This will force the compiler to use the function version because the macro no longer matches.

Function-like macros work by matching an identifier followed by a left paren (. Since we've wrapped the function name itself in parens, we have instead an identifier followed by a right paren ), which fails to match the macro. The parens are semantically transparent, but they inhibit the macro syntax.

IIRC, it was splint the C checker which taught this to me. While writing a postscript interpreter, I created nice short macros to access the stack.

#define push(o) (*tos++ = (o))
#define pop() (*--tos)

Which were great until the tricky parts where they were part of an expression involving tos. To avoid undefined behavior, I had to create function versions and use those for those tricky spots. For the new design, I skipped the macros altogether.

---

Edit: I've got a nagging feeling that it was actually the Coelocanthe book (Peter Van Der Linden's Deep C Secrets) where I learned this, the above situation being where I first needed it. IIRC his example involved putchar or getchar which are often implemented as both functions and macros in conforming C implementations.