链表复制构造函数崩溃程序 [已关闭]

问：

我不确定为什么我的复制构造函数似乎使程序崩溃，链表类中的所有其他函数都很好。5 法则现在真的让我对实现感到困惑。如果有人对我哪里出错有一些指示或指导，请告诉我，谢谢。

DList ctor：

DList() {
    //Node* front_;
    front_ = new Node(); // creating front sentinel
    //Node* back_;
    back_ = new Node(); // creating back sentinel
    //make them point to eachother
    front_->next_ = back_;
    back_->prev_ = front_;
    listSz = 0;
}

析构函数和复制构造函数：

//destructor
~DList() {

    Node* current = front_;

    while (current != back_)
    {
            front_ = front_->next_;
            delete current;
            current = front_;
    }
}
// copy ctor
DList(const DList& rhs) {
    cout << "in ctor" << endl;
    const Node* current = rhs.front_;
    Node* temp = nullptr;
    if (current != rhs.back_)
    {
        cout << "in if" << endl;
        front_ = new Node(current->data_);
        temp = front_;
        current = current->next_;
    }
    while (current != rhs.back_)
    {
        cout << "in while" << endl;
        Node* nn = new Node(current->data_);
        temp->next_ = nn;
        temp = temp->next_;
        current = current->next_;
    }
    cout << "test";
}

主要：

int main(void) {
    DList<int> list;
    DList<int> list2;
    DList<int>::const_iterator it;

    cout << list.size() << endl;
    list.push_front(1);
    list.push_front(2);
    list2.push_back(3);
    list2.push_front(4);
    list.print();

    std::cout << endl;


    list2.print();

    DList<int> list3 = list;
    list3.print();
}

崩溃前的输出：

0
2
1

4
3
in ctor
in if
in while
in while
test
2
1