Jan Engelhardt wrote:
> 0 is all-bits-zero.
> NULL is 0. ("It is.", above)
>
> Transitively, this would make NULL all-bits-zero.
> I might have missed something, though, perhaps that the cast to void* makes it
> intransitive.
It does -- a cast from integer to pointer isn't required to be a bitwise
noop. Machines on which NULL isn't bitwise zero do exist, and the C
standard allows them. What is almost certainly more common than "all
bits zero is not a NULL pointer" is "any NULL pointer is not necessarily
all bits zero"; there are quite a few machines on which there are
nonzero bitpatterns that are still valid NULL pointers, but an all-zero
memset() will still produce NULL pointers.
However, the particular supersets of the C standard that gcc provides
and which the kernel are written in (the latter being a proper subset of
the former) does not.
-hpa
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