What assumptions can I make for the local addresses of C ++ variables

Question

I wonder if I can reuse a pointer to a variable inside a loop block.

int *ptr = nullptr;
for (int i = 0; i < 5; ++i) {
    int j = 5;
    if (!ptr) ptr = &j;
    cout << *ptr << endl;
}

I believe that this code will work on all compilers, but does it comply with the standards?

Answer 1

No, that will not work.

The second iteration ptrindicates the jfirst iteration, which no longer exists. Highlighting ptrat this point is undefined behavior. The same for all iterations after the first.