Reinterpret struct with members of the same type as an array in a standard compliant way [duplicate]

Answer 1

No, it is not legal because when adding an integer to a pointer, the following applies ([expr.add]/5):

If both the pointer operand and the result point to elements of the same array object, or one past the last element of the array object, the evaluation shall not produce an overflow; otherwise, the behavior is undefined.

y occupies the memory location one past the end of x (considered as an array with one element) so adding 1 to &x is defined, but adding 2 to &x is undefined.