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Re: PR 25512: pointer overflow defined?

Gabriel Dos Reis wrote:

you can (equality) compare a pointer to NULL -- which does not even
happen to designate an object.


Well accurately, you can compare pointers, its not illegal, but the result of
comparing pointers to separately allocated objects is undefined.

[...]

| One way to think about the semantic model is to consider pointers
| in C to consist of a base/offset pair, where the base points to the
| start of the object (some debugging checkout C compilers even
| use such a format). Then operations on pointers need ONLY
| reference the offset.

that model is too simplistic -- hint: null pointers.


null is a special case indeed, which can be reprsented using a distinguished offset

-- Gaby





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