Messages in this thread | | | Date | Tue, 14 Oct 2003 11:52:36 +1000 | From | Nick Piggin <> | Subject | Re: VM code question |
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William Lee Irwin III wrote:
>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. >
AFAIKS the 0 is not part of the address calculation method though. It is only used in the argument to the typeof operator. I think 0 is used simply because its as good a place as any, right?
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