C ++链表模板和节点

Question

I'm currently attempting to create a template for my list class - which should be able to create a linkedlist of Employee classes which inherit Employee (Manager and Staff).

I'm confused as to how I initialize the list as when I do, it asks for a data type.

Here are some snipits of my code:

template <class DataType>
struct Node
{
    DataType data;
    Node<DataType> *next;
};



template <class DataType>
class List
{
public:
    List();
    List(const List<DataType> & aplist);
    ~List();

    bool search(const DataType & element);  

    Node<DataType> first();
private:
    Node<DataType>* head;
    Node<DataType>* current;              
};

template <class DataType>
List<DataType>::List() 
{
    head = NULL;
}

template <class DataType>
List<DataType>::List(const List<DataType> & aplist)
{
    deepCopy(aplist);
}
... etc

I am slightly confused when it comes to creating the list; previously when I had my linkedlist in a .header file I used List myList; so now I tried this

List<> myList;

and it expects a data type. So I tried List< DataType> myList; and it doesn't like DataType even though it's declared in my template? I also tried Node and get and error saying that the argument list for class template "Node" is missing.

I was wondering if anyone could explain how to enable my linked list (myList) to initialise and then allow entry of 3 different classes Employee (Base class), (Managerand Staff inherit Employee).

Cheers

Answer 1

I would suggest you to try your implementation with something like an int:

List<int> myList;

If that works, wour basic implementation of a linked list using a template is correct. Now you can start creating your own datatypes like an employee class (if you do not already have some) and use that one. It should work exactly the same way.

Please note that the name "DataType" in your class templates is not actually a data type, but a placeholder for a real data type like int, Employee, ...

Answer 2

You need to give the specific data type that you want the list to hold. So if it will hold Employee instances only this could be

List<Employee> myList

But if you want polymorphic behavior, then you'll need the nodes to store pointers; eg

List<Employee*> myList

Or, depending on your resource management needs

List<std::unique_ptr<Employee>> myList