Question

Can anyone explain to me why this code works (why does it return a value)?

int main()
{
    int *ptr = new int(113);
    int &rPtr = *ptr;

    delete ptr;

    cout << rPtr << endl;

    return 0;
}

Basically, this is the return value that I get:

-572662307

Answer 1

What you are doing results in undefined behavior, so the fact that you’re getting this number is perfectly reasonable behavior.

When you perform this sequence:

int *ptr = new int(113);
int &rPtr = *ptr;

The reference rPtr now refers to the integer you created with the line new int(113). On the next line, you execute

delete ptr;

This deletes that int, meaning that the object no longer exists. Any pointers or references to it now reference a deallocated object, which causes undefined behavior. Consequently, when you print rPtr with

cout << rPtr << endl; 

Anything can happen. Here, you’re just getting garbage data, but the program easily could have crashed or reported a debug error message.

Interestingly: The value you printed (-572662307), treated as a 32-bit unsigned value, is 0xDDDDDDDD. I bet this is the memory allocator putting a value into the deallocated memory to help you debug memory errors like this one.

Hope this helps!