Function dequeue

contents/tree_traversal/code/c/utility.h:92–101

}

void *dequeue(struct queue *q) {
    if (queue_empty(q)) {
        return NULL;
    }

    void *ret = q->data[q->front];
    q->front = (q->front + 1) % q->capacity;

    return ret;
}

void free_queue(struct queue q) {
    free(q.data);