Function like macros

Question

Is this valid C code:

foo.h:

#ifndef FOO_H_
#define FOO_H_

#define FUNC(var)   \
   do               \
   {                \
      //something  \
   }while(0)        \

#endif

foo.c:

#include <stdio.h>
#include "foo.h"

FUNC(5); //How is it possible to call the function-like macro from here?

int main(void)
{
   //do something
   return 0;
}

I have some (working) code that is arranged like this, and in global scope calling a function-like macro. How is this possible?

Answer 1

I have some (working) code that is arranged like this, and in global scope calling a function-like macro. How is this possible?

There is nothing inherently wrong with a function-like macro being invoked at file scope. It's all a question of the macro's replacement text, in light of its arguments. The function-like macro you present in the question cannot be invoked at file scope because it expands to a do / while statement, and those must appear inside functions. Whatever example you are thinking of that works cannot have the same kind of replacement text.

Here's an example demonstrating a function-like macro that can be expanded at file scope:

#include <stdio.h>

#define DECL_INT(v,i) int v = (i)

DECL_INT(var, 42);

int main(void) {
    printf("%d\n", var);
}

That means exactly the same thing as ...

#include <stdio.h>

int var = (42);

int main(void) {
    printf("%d\n", var);
}