Technically the array subscript example is UB even before the dereference. a[1][7] is equivalent to `*(a[1] + 7)` and a[1] + 7 itself is UB. (6.5.7) Additive o

Technically the array subscript example is UB even before the dereference. a[1][7] is equivalent to `*(a[1] + 7)` and a[1] + 7 itself is UB. (6.5.7) Additive operators > If the pointer operand and the result do not point to elements of the same array object or one past the last element of the array object, the behavior is undefined. Interestingly a[1][5] is also UB, but for the dereferencing a past-the-end pointer, not for the arithmetic.