Function returns null pointer instead of address

Question

I'm playing around with pointers to understand this concept better and wanted to ask

Why do i get null pointer as return for the second function?

and why it isn't possible to get the address 0x7fff15504044. What is happening and where inside memory is the integer 5 stored, when im working with it inside the function?.

#include <iostream>
using namespace std;

int* return_adress(int* input){ return input; }

int* return_adress_from_input(int input){ return &input; }

int main(){
    int k = 3; 
    cout << return_adress(&k) << endl;
    cout << return_adress_from_input(k) << endl;
}

Output:

0x7fff15504044

0

Answer 1

With int* return_adress_from_input(int input), input is a value copy of k in the caller. They are two different variables therefore with different addresses.

input goes out of scope conceptually once the closing brace of the function is reached.

The pointer &input then points to memory that you no longer own, and the behaviour of reading that pointer value (let alone dereferencing it) is undefined prior to C++14, and implementation defined from and including C++14.