C/C++ Structure offset

I'm looking for a piece of code that can tell me the offset of a field within a structure without allocating an instance of the structure.

IE: given

struct mstct {
    int myfield;
    int myfield2;
};

I could write:

mstct thing;
printf("offset %lu\n", (unsigned long)(&thing.myfield2 - &thing));

And get offset 4 for the output. How can I do it without that mstct thing declaration/allocating one?

I know that &<struct> does not always point at the first byte of the first field of the structure, I can account for that later.