Reading old pointer values in the new pointer

Asked Oct 18 '19 at 12:02

Active Oct 18 '19 at 12:02

Viewed 38 times

I am aware of pointer and memory allocation but I am not getting the below program. I am getting wrong output.

int main()
 {
    int *old = new int(10);
    cout<<*old<<" "<<old<<endl;  //10 0x1b3ac20(Address)
    delete old;
    cout<<*old<<" "<<old<<endl;  //0 0x1b3ac20(Address)
    *old = 20;
    cout<<*old<<" "<<old<<endl;  //20 0x1b3ac20(Address)

    int *latest = new int(12);
    cout<<*latest<<" "<<latest<<endl; //12 0x1b3ac20(Address)  
    delete latest;
    cout<<*latest<<" "<<latest<<endl; //20 0x1b3ac20(Address). why 20?
    return 0;
 }

I don't understand the below statements.

delete old;
*old = 20;--------------------------->How can we assign value if memory deleted
cout<<*old<<" "<<old<<endl;-------(1)

delete latest;--------------------------------(2)
cout<<*latest<<" "<<latest<<endl;------------->If I delete the latest then why *latest still printing 20

asked Oct 18 '19 at 12:02

Ramkumar lodhi

1

`*old = 20;` has Undefined Behaviour. Anything can happen. It may even look like the program is working - until it's not. – Ted Lyngmo Oct 18 '19 at 12:05
Where did you get that code? that's so ugly to see that :O – damadam Oct 18 '19 at 12:05
1

You're getting the right Output – nada Oct 18 '19 at 12:05
2

Anything you do with a pointer value after `delete` is [undefined behavior](https://stackoverflow.com/questions/2397984/undefined-unspecified-and-implementation-defined-behavior?r=SearchResults&s=2|264.6429). This simply is not worth reasoning about. – StoryTeller - Unslander Monica Oct 18 '19 at 12:06

Reading old pointer values in the new pointer

0 Answers0