Question

Is it possible to define a macro in a C file, and then change behavior of another C file using this definition?

For instance, suppose we have a file named b.c:

#include <stdio.h>
#define ABC

void function() {
    printf("b.c\n");
}

And another file named a.c:

#include <stdio.h>

int main() {
    #ifdef ABC
        printf("b.c defined this\n");
    #endif
    printf("a.c\n");
}

These files are compiled together. I want the definition of ABC in b.c to influence a.c.

I know I was supposed to be using a header file, but I don’t want to do that. Is there another way to achieve this?

In my scenario, b.c is a sort of sub-application that will complement the behavior of a.c, and it should also be able to override behavior in there.

Is there an alternative to macros that can achieve this?

Answer 1

Use global variables or use callbacks. The “best” solution depends on precisely how much flexibility you need.