Question

What error is thrown when macro and function conflict in C arises?
Is it a macro processor error or does this error occur due to some language violation?

For example, in this code:

#include <stdio.h>
#define MAX(i, j) (i>j)? i : j

int MAX(int i, int j){
  return (i>j) ? i : j;
}

int main(){
  int max = MAX(5, 7);
  printf("%d",max);
  return 0;
}

The program throws a compile time error. But I don’t understand whether it was some language violation or macro expansion error or something else.

Answer 1

During the preprocessing phase the code gets converted to :

int (int i>int j)? int i : int j{
  return (i>j) ? i : j;
}

int main(){
  int max = (5>7)? 5 : 7;
  printf("%d",max);
  return 0;
}

…which, as anyone can tell, is an illegal C code.

(With gcc you could use an -E option to see the preprocessed version of the file.)