value inside a linked lists Node exists after change, why?-CodePudding

lets say we have a linked list = [1] -> [2] -> [3] -> [4]

typedef struct Node
{
    int val;
    struct Node* next;
}Node;

I have the head and to free all the allocated memory I do

printf("%i", head->val); // prints 1

Node* tmp = head;
while(tmp != NULL)
{
    Node* tmp2 = tmp;
    tmp = tmp->next;
    free(tmp2);
}

printf("%i", head->val); // prints a big number, but exists and is not NULL

if (tmp == NULL)
{
    print("is null"); // this prints too
}

why head->val still exists and tmp doesn't? shouldn't head->val be NULL after freeing it ? I assumed since head is a pointer itself and i set it to another pointer then its pointing at the location anyway so when I free tmp it should free the thing in the address that head is pointing to aswell?

CodePudding user response：

As stated in comments, attempting to access member of head after freeing it invokes undefined behavior. head->val might be NULL, or it might still have a value because that memory has not been overwritten.

The point of undefined in "undefined behavior" is that we don't know and can't know for sure what will happen.