为什么 C++ 不能同时释放内存和指针

Question

I have learned that in C++(download form VSCode 0.26.3) although a memory have already been freed, the pointers pointed to it won't change, which means they won't be NULL.

Is there any method can let the pointer be NULL?

Answer 1

No there is no method to do this automatically and it is important to realize that also setting the pointer to nullptr manually wont solve the general problem. To see why, consider this simplified example:

int* x = new int(5);
int* y = x;
delete x;
x = nullptr;
if (x) // attempt to check if x still points to an object
    std::cout << *x;
if (y) // attempt to check if y still points to an object
    std::cout << *y;  // !! UNDEFINED BEHAVIOR !!

It is common to see pointers being set to nullptr after the call to delete . However, imagine y is not in the same scope as x but some other object holds y , then there is no way that other object "knows" that y is no longer a valid pointer.

To avoid this and other problems smart pointers have beeen introduced and raw pointers should be avoided.

Answer 2

If you are using raw pointer then whenever you release memory assign pointer to NULL explicitly. There is no automatic way for raw pointers.