On Tue, Oct 14, 2003 at 11:32:27AM +1000, Darren Williams wrote:
I have a small question wrt some VM code.
source file is include/linux/kernel.h
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
what is the use of the 0 (zero) in the typeof? I am thinking
that we are casting 0 to (type *) then referencing 'member' of
'type', however why do we require the 0 ?
Just curious
It's an address calculation method. We subtract the address of the
start of the structure from the address of the member inside the
structure.