How does this work? Pointer to pointer assignment

Question

#include <iostream>
using namespace std;
int main() {
    int *p1;
    p1 = new int;
    int *p2;
    p2 = new int;
    p2 = p1;    // what happens here?
    *p1=5;
    cout << "pointer 2 is " << *p2 << endl << *p1 << endl;  // both give out 5
    delete p1;  // what happens to p2 ?
    cout << "pointer 2 is " << *p2 << endl;
    delete p2;
    return 0;
}

What happens when I delete the pointer object p1? What is pointer p2 referencing now ? Can some one explain ? Thanks for the help

Answer 1

What is pointer p2 referencing now ?

Nothing. It's dangling. It was pointing to the same thing p1 was pointing to, but you've deleted that.

Consequently, your *p2 is broken, as is your delete p2; these both have undefined behaviour.

You've also leaked the second new int, because p2 used to point to it but stopped doing so when you wrote p2 = p1 (you changed it to point to the first new int instead, like p1 does), and there's no other way to refer to it.