Re: VM code question

[William Lee Irwin III]

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.


-- wli
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