container-of Implementation

[Schrober]

Hi,

I wondered why the container_of implementation is so complicated.

#define container_of(ptr, type, member) ({			\
	const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
	(type *)( (char *)__mptr - offsetof(type,member) );})

isn't the __mptr not unnecessary? Why not following version?

#define container_of(ptr, type, member) \
    ((type *)((char *)(ptr) - offsetof(type, member)))
-- 
Franz Schrober
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