On Mon, Mar 12, 2018 at 11:19:39AM +0800, Yubin Ruan wrote: > Hi, > > I notice that in the implementation of container_of(), the resulting pointer > will be advanced by 1 if types mismatch: > > #define container_of(member_ptr, containing_type, member) \ > ((containing_type *) \ > ((char *)(member_ptr) \ > - container_off(containing_type, member)) \ > + check_types_match(*(member_ptr), ((containing_type *)0)->member)) > > where check_types_match() is defined as > > #define check_types_match(expr1, expr2) \ > ((typeof(expr1) *)0 != (typeof(expr2) *)0) > > which will return 1 if types mismatch.
No.. it won't, it will have a type error. That's not typeof(x) ==
typeof(y), which isn't valid C (or gcc) in any case. It's checking if
NULL (0) cast to the first pointer type equals NULL cast to the second
pointer type. If the types mismatch, there will be a type error.
> IMO, advancing the wrong pointer (resulting from mismatch types) by 1 will
> only make things worse, and users usually only get garbage results and will
> not
> be aware of the type-mismatch bug. Wouldn't it be better to throw an building
> error/warning for that?
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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