错误未命名类型

Question

I'm getting the compiler error: error "Node" does not name a type. This is my header:

#ifndef LINKEDLIST_H
#define LINKEDLIST_H



template <class ItemType>
class LinkedList
{
public:
    LinkedList(); // Constructor

    bool isEmpty() const; // Checks if list is empty.
    int getLength() const; // Returns the amount of times in the list.
    bool insert(int index, const ItemType& insertItem); // Inserts an item at index.
    bool remove(int index);  // Removes item at index.
    void clear();  // "clears" the list, but actually sets amount of items to zero.
    ItemType getIndex(int index);  // Returns the item at a given index.
    int find(const ItemType& findItem);  // Finds an item, then returns the index it was found.
    void printList() const;

private:
    struct Node // Struct so I can have my linked list.
    {
        ItemType item; // Data item.
        Node* next; // Pointer to the next node.
    };

    int itemCount; // Current amount of items in list.
    Node* headPtr; // Head/beginning of the list.

    Node* getNodeAt(int position) const; // Private method to get position.
};
#include "LinkedList.cpp"
#endif // LINKEDLIST_H

Then my cpp:

#include "LinkedList.h"
#include <iostream>
using namespace std;

// All the other methods, and at the very end...

template<class ItemType>
Node* LinkedList<ItemType>::getNodeAt(int position) const //Error is here.
{
    Node* retPtr = headPtr;
    int index = 0;
    while(index != position)
    {
        retPtr = retPtr->next;
        index++;
    }
    return retPtr;
}

The error is at the method signature in the cpp file for getNodeAt. From what I've read, it seems the errors come about when an object is referenced that isn't already defined, but I'm not really seeing how I've made that error.

Answer 1

// All the other methods, and at the very end...

template<class ItemType>
Node* LinkedList<ItemType>::getNodeAt(int position) const //Error is here.
{
    Node* retPtr = headPtr;
    int index = 0;
    while(index != position)
    {
        retPtr = retPtr->next;
        index++;
    }
    return retPtr;
}

Node is a member struct of an encompassing struct, so do LinkedList<ItemType>::Node* in the return type as you've not yet entered the LinkedList<ItemType> scope.

Also, if that template function is used by any other file directly (or through another template function), you'll probably have to move it to your header file at one point or you'll get another compiler error.

Answer 2

The error is correct: there is no Node type anywhere in your program. However there is a LinkedList<ItemType>::Node type. Use it instead.

Another problem: you should not include LinkedList.cpp in LinkedList.h . And certainly you should not include LinkedList.h in LinkedList.cpp if you do include .cpp file. General approach is to implement all template code in header. If you want to sepatate implementation and include it in header then do not include header in implementation and give it extention different from source code extention to not confuse build system.