首先：你的方法DblLinkedBag :: clear有一个错误，nodeToDelete永远不会改变（只是删除第一个节点）

First: your method DblLinkedBag::clear has a error, nodeToDelete never change (just deletes first node)

bool DblLinkedBag::remove(string item)
{
    node* curPtr=start;

    while (curPtr!=NULL)
    {
        if(item==curPtr->data)
        {
            if(curPtr->prev) curPtr->prev->next = curPtr->next;
            if(curPtr->next) curPtr->next->prev = curPtr->prev;
            delete curPtr;
            itemCount--;
            return true;
        }
        else
        {
            curPtr=curPtr->next;
        }
    }
    return false;
}

你希望getFrequency（）做什么？

What do you expect getFrequency() to do?