链表内的链表与模板

Question

我基本上是建立一个数据库结构，我可以添加联赛，足球队和固定装置。我做了一个链表模板，并在每支球队和每个联赛的球队链表的装置链表。我也有一个联赛的链表在我的dataBase类。我已经设法添加了添加联赛到数据库的功能，但现在我不能添加一个团队。我已经完成了我的add函数，它分配了正确的值，但是当从函数返回时，指定联赛中的team_list链表为空。

这是我的addTeam函数在数据库中。

void Database::addTeam(Team team)
{
    Node<League>* ptr = league_list.getHead();
    while(ptr!=0)
    {
        // if the team's league matches current in the list add to this league
        if(ptr->getData().getLeagueName()==team.getLeagueName())
        {
            ptr->getData().getTeamList().add(team);
            return;
        }
        else // doesn't match so go to next league in list
        {
            ptr=ptr->getNextNode();
        }
    }
    if(ptr==NULL) // if not found prompt user
    {
        throw exception(ERRORMSG);
    }
}

这是我在链表中的add函数。当我在调试器中逐步执行时，这似乎修改和改变了预期的值。但是，当它从这个函数返回到数据库中的addTeam函数时，没有任何变化。

template<class data>
void LinkedList<data>::add(data a)
{
    Node<data> *nodePtr;
    nodePtr=new Node<data>(a);
    nodePtr->setNextPointer(0);
    if(head==0) // if head is empty
    {
        head=nodePtr; // make the new node the first node
        head->setPreviousPointer(0); // make the new node point to null
    }
    else
    {
        if(nodePtr==0) // if head is null
        {
            last=0; // if list unoccupied _last is null
        }
        while(nodePtr->getNextNode()!=0)
        {
            last=nodePtr->getNextNode();
        }
        nodePtr->setPreviousPointer(last);
        // set the old last node to point to the new node
        last->setNextPointer(nodePtr);
    }
    last=nodePtr;       // point to the new end of list
    current=nodePtr;    // set the current node to the last in list
}

如果你能告诉我为什么会这样，我将非常感激。

Answer 1

您的addTeam函数存在一些问题:

template<class data>
void LinkedList<data>::add(data a)
{
    Node<data> *nodePtr;
    nodePtr=new Node<data>(a);
    // this should not be necessary, do that in the constructor of Node
    nodePtr->setNextPointer(0);
    if(head==0) // if head is empty
    {
        head=nodePtr; // make the new node the first node
        // this is not necessary, nodePtr already has been set up above
        // not to have a next node
        // head->setPreviousPointer(0); // make the new node point to null
    }
    else
    {
        // this check will never fail; what do you want to check here?
        if(nodePtr==0) // if head is null
        {
            last=0; // if list unoccupied _last is null
        }
        // this loop will never run
        /*
        while(nodePtr->getNextNode()!=0)
        {
            last=nodePtr->getNextNode();
        }
        */
        // either you have stored a Node<data>* last as member of LinkedList
        // or you need something like
        Node<data>* last = head;
        while(last->getNextNode() != 0)
        {
            last = last->getNextNode();
        }
        nodePtr->setPreviousPointer(last);
        // set the old last node to point to the new node
        last->setNextPointer(nodePtr);
    }
    last=nodePtr;       // point to the new end of list
    current=nodePtr;    // set the current node to the last in list
}