------- Additional Comments From falk at debian dot org 2005-07-15 06:41 ------- Subject: Re: pointer +- integer is never NULL
"gdr at integrable-solutions dot net" <[EMAIL PROTECTED]> writes: > My indirect observation was that reinterpret_cast is intended for > specific needs that cannot adequately be expressed at the purely > object type level. The result is intended to be unsurprising to > those who know the addressing structure. Consequently it takes a > creative compiler to make reinterpret_cast<int*>(0) + 5 undefined. Sorry, I cannot follow you. I'd find it massively unsurprising if reinterpret_cast<int*>(0) produces a null pointer, and if I then get undefined behavior for doing something with it that is undefined for a null pointer. In fact I'd find it very *surprising* if reinterpret_cast<int*>(0) behaves different than a normally constructed null pointer anywhere. > Furthermore, given the mapping chosen by GCC, it takes even more > creative compiler to make (int *)0 + 5 also undefined. And I don't see how that follows, either. As it seems, arguing with different levels of surprisingness seems to be somewhat subjective, so I don't think this leads us anywhere. > There still are reasonable codes for system programming out there > that needs the to go through the play with null pointer -- we, GCC, > even used to distribute such things in the past. This is a more relevant point. I don't think this optimization would break offsetof-like macros, since they'd use null pointer *constants*, which we could easily avoid to tag as non-null. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22485
