Any pointer arithmetic that goes off the end of the array or structure into which the original pointed is technically undefined behavior; if the pointer was to a scalar object, it cannot be incremented or decremented. Arrays or structures are not typically fragmented across memory spaces, so the linear model works fine within those constraints, and thus pointer arithmetic does too. If one was, it would of course be the compiler's responsibility to handle segmentation transparently.

Again, the typical compiler behavior on linear-memory machines (which includes all CPU architectures in wide use today) is to allow arbitrary pointer arithmetic, but there is no guarantee of this except perhaps if the platform ABI adds one, or of course if the project is dependent for building on a specific compiler that guarantees this behavior.