这是一个双链表，为什么第二个函数不能实现逆序输出？

doubleNode *DoubleList::initChain_end() {
    auto *head = new doubleNode;
    auto prev = head;
    cout << "How many?";
    int num;
    cin >> num;
    for (int i = 0; i < num; ++i) {
        auto temp = new doubleNode;
        temp ->data = i;
        prev ->next = temp;
        temp ->prior = prev;
        prev = temp;
        temp ->next = nullptr;//少写则异常输出
    }
    while(head) head = head ->next;
    return head;
}

void DoubleList::display(doubleNode *head) {
    auto cur = head -> prior;
    while (cur){
        cout << cur -> data << " ";
        cur = cur -> prior;
    }
}

这是一个双链表，为什么第二个函数不能实现逆序输出？（我想从后向前迭代）我在15行已将把head指向最后一个位置了。理论上我每次都把cur指向前一个指针域就行了啊，为什么每次输出都是空？

while(head) head = head ->next; 这个循环结束，head肯定是空的啊
改成while(head->next != NULL) head = head->next;