Messages in this thread | | | Date | Mon, 13 Oct 2003 18:44:27 -0700 | From | William Lee Irwin III <> | Subject | Re: VM code question |
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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.
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