Is it undefined behavior to form a pointer range from a stack address?

Question

Some C or C++ programmers are surprised to find out that even storing an invalid pointer is undefined behavior. However, for heap or stack arrays, it\'s okay to store the a

Answer 1

5.7-5 of ISO14882:2011(e) states:

When an expression that has integral type is added to or subtracted from a pointer, the result has the type of the pointer operand. If the pointer operand points to an element of an array object, and the array is large enough, the result points to an element offset from the original element such that the difference of the subscripts of the resulting and original array elements equals the integral expression. In other words, if the expression P points to the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and (P)-N (where N has the value n) point to, respectively, the i + n-th and i − n-th elements of the array object, provided they exist. Moreover, if the expression P points to the last element of an array object, the expression (P)+1 points one past the last element of the array object, and if the expression Q points one past the last element of an array object, the expression (Q)-1 points to the last element of the array object. 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.

Unless I overlooked something there, the addition only applies to pointers pointing to the same array. For everything else, the last sentence applies: "otherwise, the behaviour is undefined"

edit: Indeed, when you add 5.7-4 it turns out that the operation you do is (virtually) on an array, thus the sentence does not apply:

For the purposes of these operators, a pointer to a nonarray object behaves the same as a pointer to the first element of an array of length one with the type of the object as its element type.