Question

Consider the following structure definitions and fill in the blanks for the dequeue function:

    typedef struct queue queue_t;
    typedef struct node node_t;

    struct node {
        node_t *next;
         void *val; };

    struct queue {
        node_t *head;
        node_t *tail;};

/* removes and returns the item at the head of the queue q,
 * or NULL if q is empty. */

void *dequeue (queue_t *q) {
    if (q->head == NULL) {

        return NULL;
    }

    void *val = __________________________;
    node_t *p = __________________________;
    q->head = __________________________;
    free(p);

    if (q->head == NULL) {
        q->tail = NULL; 
    }

return val; }

Answer 1

I would like to suggest some errors in the code. First of all, the dequeue functions return type is void. Therefore, it cannot return val.

The answer:

void *val = q->head;

node_t *p = q->head;

q->head = q->head->next;