C/C++ Structure offset

Question

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

Answer 1

How about the standard offsetof() macro (in stddef.h)?

Edit: for people who might not have the offsetof() macro available for some reason, you can get the effect using something like:

#define OFFSETOF(type, field)    ((unsigned long) &(((type *) 0)->field))

Answer 2

Right, use the offsetof macro, which (at least with GNU CC) is available to both C and C++ code:

offsetof(struct mstct, myfield2)

Answer 3

printf("offset: %d\n", &((mstct*)0)->myfield2);