Why subtract null pointer in offsetof()?
- by Bruce Christensen
Linux's stddef.h defines offsetof() as:
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
whereas the Wikipedia article on offsetof() (http://en.wikipedia.org/wiki/Offsetof) defines it as:
#define offsetof(st, m) \
((size_t) ( (char *)&((st *)(0))->m - (char *)0 ))
Why subtract (char *)0 in the Wikipedia version? Is there any case where that would actually make a difference?