Most underlying implementations won't actually dereference here (which is why it usually works), but as far as the spec is concerned, you are dereferencing it,

Most underlying implementations won't actually dereference here (which is why it usually works), but as far as the spec is concerned, you are dereferencing it, which is undefined. That becomes a problem with modern optimizing compilers, because they make assumptions about your code based on what's allowed according to the spec.