Robert Dewar <[EMAIL PROTECTED]> writes: | Richard Guenther wrote: | | >On Wed, 21 Dec 2005, Andrew Haley wrote: | > | > | >>Richard Guenther writes: | >> > > The problem in this PR is that code like in the testcase (from | >> > OpenOffice) assumes that pointer overflow is defined. As the | >> > standard does not talk about wrapping pointer semantics at all (at | >> > least I couldn't find anything about that), how should we treat | >> > this? | >> | >>Look at Section 6.5.6, Para 8. The code is undefined. | >> | > | >This talks about pointers that point to elements of an array object. | >It does not talk about doing arithmetic on arbitrary pointer (constants), | >which is what the code does. | > | Right, but that's the point. "doing arithmetic on arbitrary pointer" | values is | not defined,
I think that needs qualification, given the semantics of pointer -> integer type integer type -> pointer conversions. |it is not even defined to compare two pointers pointing to two | different objects. you can (equality) compare a pointer to NULL -- which does not even happen to designate an object. [...] | 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. -- Gaby
