On Sat, 27 Dec 2003 15:40:10 -0800, Kevin D. Quitt
<KQ**********@I EEIncUNMUNG.com > wrote:
On Thu, 18 Dec 2003 18:55:37 +0000 (UTC), Christopher Benson-Manica
<at***@nospam. cyberspace.org> wrote:
Is (a+17)==&b a legal comparison?
No. They aren't pointers to the same object.
Apparently they don't have to be - 6.5.9:
6 Two pointers compare equal if and only if both are null pointers, both
are pointers to the same object (including a pointer to an object and a
subobject at its beginning) or function, both are pointers to one past the
last element of the same array object, or one is a pointer to one past the
end of one array object and the other is a pointer to the start of a
different array object that happens to immediately follow the first array
object in the address space.
I am surprised by that last. OTOH, 6.5.8.5:
When two pointers are compared, the result depends on the relative
locations in the address space of the objects pointed to. If two pointers
to object or incomplete types both point to the same object, or both point
one past the last element of the same array object, they compare equal. If
the objects pointed to are members of the same aggregate object, pointers
to structure members declared later compare greater than pointers to
members declared earlier in the structure, and pointers to array elements
with larger subscript values compare greater than pointers to elements of
the same array with lower subscript values. All pointers to members of the
same union object compare equal. If the expression P points to an element
of an array object and the expression Q points to the last element of the
same array object, the pointer expression Q+1 compares greater than P. In
all other cases, the behavior is undefined.
That last sentence would seem to make a comparison of a+17 and &b UB.
--
#include <standard.discl aimer>
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