Is pointer arithmetic on allocated storage UB?

Question

Let\'s say I want to implement std::vector without invoking any undefined behavior (UB). Is the code below invokes UB:

struct X{int i;};
int main(){
  auto p         


        

Answer 1

Yes, technically it has undefined behaviour, though we tend to ignore that. P0593 should fix it properly.

The phrase "possibly-hypothetical" refers to one-past-the-end "elements" (ref), and does not permit this case.