Is there a standard pointer size declaration?

Question

I have struct with padding in char (oops, my bad). I would like to subtract a pointer size. Do you know a standard pointer size declaration, or a standard macro

Answer 1

If you are looking for a portable way to find the offset in bytes of a structure member then you want to use the offsetof() macro defined in stddef.h:

#include 
#include 

int main(void)
{
    struct s {
        int i;
        char c;
        double d;
        char a[];
    };

    /* Output is compiler dependent */

    printf("offsets: i=%ld; c=%ld; d=%ld a=%ld\n",
            (long) offsetof(struct s, i),
            (long) offsetof(struct s, c),
            (long) offsetof(struct s, d),
            (long) offsetof(struct s, a));
    printf("sizeof(struct s)=%ld\n", (long) sizeof(struct s));

    return 0;
}

Output

$ ./a.out
offsets: i=0; c=4; d=8 a=16
sizeof(struct s)=16