Finding offset of a structure element in c

Question

struct a
{
    struct b
    {
        int i;
        float j;
    }x;
    struct c
    {
        int k;  
        float l;
    }y;
}z;

Can anybody

Answer 1

struct a foo;
printf("offset of k is %d\n", (char *)&foo.y.k - (char *)&foo);    
printf("offset of i is %d\n", (char *)&foo.x.i - (char *)&foo);

foo.x.i refers to the field i in the struct x in the struct foo. &foo.x.i gives you the address of the field foo.x.i. Similarly, &foo.y.k gives you the address of foo.y.k; &foo gives you the address of the struct foo.

Subtracting the address of foo from the address of foo.x.i gives you the offset from foo to foo.x.i.

As Gangadhar says, you can use the offsetof() macro rather than the pointer arithmetic I gave. But it's good to understand the pointer arithmetic first.