If any of the operands is a pointer, the following rules apply:

* A pointer to non-array object is treated as a pointer to the first element of an array with size 1.
* If the pointer P points to the ith element of an array, then the expressions P+n, n+P, and P-n are pointers of the same type that point to the i+nth, i+nth, and i-nth element of the same array, respectively. The result of pointer addition may also be a one-past-the-end pointer (that is, pointer P such that the expression P-1 points to the last element of the array). Any other situations (that is, attempts to generate a pointer that isn't pointing at an element of the same array or one past the end) invoke undefined behavior.
* If the pointer P points to the ith element of an array, and the pointer Q points at the jth element of the same array, the expression P-Q has the value i-j, if the value fits in std::ptrdiff_t. Both operands must point to the elements of the same array (or one past the end), otherwise the behavior is undefined. If the result does not fit in std::ptrdiff_t, the behavior is undefined.
* In any case, if the pointed-to type is different from the array element type, disregarding cv qualifications, at every level if the elements are themselves pointers, the behavior of pointer arithmetic is undefined. In particular, pointer arithmetic with pointer to base, which is pointing at an element of an array of derived objects is undefined.
* If the value ​0​ is added or subtracted from a pointer, the result is the pointer, unchanged. If two pointers point at the same object or are both one past the end of the same array, or both are null pointers, then the result of subtraction is equal to (std::ptrdiff_t)0.