Comparator as function parameter

Question

Is there any possibility in C89 to pass an operator as function parameter? I mean pass for expample <, ==, >= etc. Something like custom comparator in Java, but passed only with particular symbol. Maybe there is solution with special kind of preprocessor macro (I try to use '#' taken from processor macros)?

I know about pointers to functions, but I want something a little bit different.

---

Example:

void fun(int a, int b, comperator)
{
    if(a comperator b)
        ........
}

Answer 1

You can use a macro. But remember - a macro is not a function; it has different (ugly) syntax, some specific problems, some advantages, etc.

Suppose you have a function:

int fun(int x, int y)
{
    if (x < y)
        return 1;
    else if (x < 2 * y)
        return 2;
    else if (x < 2 * y)
        return 3;
    else
        return 4;
}

To use a different comparator, first convert it to a macro:

#define FUN(x, y) \
x < y ? 1 : \
x < 2 * y ? 2 : \
x < 3 * y ? 3 : \
4

This conversion is very ugly (it will usually by more ugly than in my example), and not always possible, but now you can add a comparator:

#define FUN(x, y, c) \
x c y ? 1 : \
x c 2 * y ? 2 : \
x c 3 * y ? 3 : \
4

Usage:

printf("%d\n", FUN(3, 5, <));

(Note: in macros, you should add parentheses around variables, explained e.g. here; I omitted them for clarity).