c ++ 2指向同一对象的指针

Question

I'm wondering if I have 2 pointers pointing same object, and then I delete it using pointer 1, will it still be in memory and pointer 2 will point null, or object will stay in memory and I need to use delete pointer 2 to free it?

I mean:

int *p1, *p2;
p1=new int;
p2=p1;
*p1=5;
p2=p1;
delete p1;

int x=*p2;
//Error or x=5?

Answer 1

• The object will be gone .
• Pointer 2 will not be a null pointer, but a dangling pointer, with its previous but now-invalid value; doing anything with it will be an error. ¹
• That's exactly true for pointer 1, too. There will be no difference between the two.

---

^{1 - Well, UB, not an "error" per se. But don't do it.}

Answer 2

It's generally good not to have two pointers pointing to the same memory. That's because if you delete one, the other will be a dangling pointer.

Anything you do with the memory after deleting it is undefined behavior .

In your case ( I assume you forgot to do p2=p1 , as your question suggests ), int x=*p2; is undefined, since the memory p2 points to was deleted.