C language: Releasing memory of pointers to struct

Question

Say I have declared a pointer to a struct and assign it with malloc() using this definition

typedef struct node {
    int info;
    struct node *next;
} NODE;

Then somewhere in the code I declared two pointers to it

NODE *node1, *node2 = NULL;

node1 = malloc(sizeof(NODE));
node2 = node1;

My question, should I use "free()" to release node2 just like people always do to node1 via free(node1). What's exactly the effect of the assignment node2 = node1;

Thanks.

Answer 1

When you do

node1 = malloc(sizeof(NODE));

you have something like

+-------+      +-----------------------------+
| node1 | ---> | memory for a NODE structure |
+-------+      +-----------------------------+

After the assignment node2 = node1 you have instead this:

+-------+
| node1 | -\
+-------+   \    +-----------------------------+
             >-> | memory for a NODE structure |
+-------+   /    +-----------------------------+
| node2 | -/
+-------+

In other words you have two pointers pointing to the same memory.

Attempting to call free using either of the two pointer variable will invalidate both pointers.