Question

#define L 1
#define M L+1

int main(void){

    int N=L*M*2;
    char s [N]={'1','2'};
    printf("%d", sizeof(s));

    return 1;   
}

Why does the above code cannot be compiled? The compiler of Eclipse says two things:

1. Variable-sized object may not be initialized: Is because the definition of N with M and L at the macro or is it because I can’t initialize an array with type arr[x] where x is variable under any circumstances?
2. excess elements in array initializer– What does it mean?

Answer 1

because I can’t initialize an array with type arr[x] where x is variable?

Indeed, pre-C99, the array size must be a constant expression. In C99, this has been relaxed with variable-length arrays.

(This is is nothing to do with macros.)

excess elements in array initializer- What does it mean?

Fix the first problem, and this should go away.