Question

I’m trying to destroy my deque but somehow I fail with pointers. I have written the following code (deque is a pointer to a pointer, which points to the first element of the deque). The DequeItem’s are structs with fields next (pointer to next element) and data (void *).

void deque_destroy(DequeItem **deque) {
    DequeItem *temp;
    DequeItem *item;
    for (item = *deque; item != NULL; item = temp) {
        printf("%d", *((int*)((item)->data)));
        temp = item->next;
        free(item);
    }
}

The struct declaration is:

struct DequeItem {
  void *data;                  // Data stored in the deque item

  struct DequeItem *previous;  // Pointer to the previous DequeItem in the ring
  struct DequeItem *next;      // Pointer to the next DequeItem in the ring
};

typedef struct DequeItem DequeItem;

Answer 1

The problem was, that the next-pointer of the last element (back element) in the deque will point to the first element (front element) even though the first element has been destroyed. I fixed this by setting

(*deque)->previous->next = NULL

before the for-loop above. Thanks for help!