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

It's been 3 years since the question has been asked, I'm adding my answer for the sake of completeness.

The hacky way of getting the offset of a struct member goes like this

printf("%p\n", (void*)(&((struct s *)NULL)->i));

It doesn't look pretty, I can't think of anything in pure C (which can get you the offset of the member, without knowing anything else about the structure. I believe the offsetof macro is defined in this fashion.

For reference, this technique is used in the linux kernel, check out the container_of macro :

http://lxr.free-electrons.com/source/scripts/kconfig/list.h#L18

A more elaborate explanation can be found in this article:

http://radek.io/2012/11/10/magical-container_of-macro/