In C a NULL is often a valid non-dereferencable pointer value. If you're checking for invalid pointer values you need to check for any of the 0xfffffffffffffffe

In C a NULL is often a valid non-dereferencable pointer value. If you're checking for invalid pointer values you need to check for any of the 0xfffffffffffffffe possible invalid values. If all you're doing is checking for NULL you're not checking for invalid values at all. If the precondition of your function is "parameter p can not be NULL" that's fine, go ahead and check for it. If the precondition is "parameter p must be a valid pointer" well then, good luck to you finding the appropriate assertion condition.