Using struct as private member to define ListNode within link list class

Question

i am trying to implement a LinkList class with a struct as my private member, however, when i try to define the struct ListNode under the LinkList.ccp, the compiler says that the pointer is not defined. The error is on the high lighted line

#ifndef LINKLIST_H
#define LINKLIST_H

#include <iostream>
using namespace std;

template <typename T>
class LinkList{
private:
    struct ListNode{
        T item;
        ListNode * next;
    };
    int size; // the size of the listNodes.
    ListNode* _head;

public:
    LinkList(); // constructor
    void giveup(int n);
    bool isEmpty();
    int getLength();

    ListNode * find(int index);
};

#endif

#include "LinkList.h"

template <typename T>
LinkList<T>::LinkList(){
    _head = NULL;
    size = 0;
}

template <typename T>
void LinkList<T>::giveup(int n){
    cout << "The error " << n << " has occured" << endl;
}

template <typename T>
bool LinkList<T>::isEmpty(){
    return (size == 0);
}

template <typename T>
int LinkList<T>::getLength(){
    return size;
}

template <typename T>
***ListNode * LinkList<T>::find(int index){ // pointer not defined***
    if(index < 1 || index > size){
        return NULL;
    }
    ListNode * currentNode = _head;
    for(int pos =2; pos <=index; pos++){
        currentNode = currentNode->next;
    }
    return currentNode;
}

score 0 · Answer 1 · edited May 23 '17 at 11:49

0

In a member function definition outside the class, a leading return type isn't scoped within the class, so you have to qualify it if it's a nested type:

template <typename T>
LinkList<T>::ListNode * LinkList<T>::find(int index)
^^^^^^^^^^^^^

The parameter list and any trailing return type is scoped within the class, so (in C++11 or later) you could write this as

template <typename T>
auto LinkList<T>::find(int index) -> ListNode *

Once you've fixed that then, in order to use the template, you'll need to move the function definitions into the header file, as described here.

edited May 23 '17 at 11:49

Community

1
1

answered Sep 16 '14 at 12:40

Mike Seymour

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Thank you for the prompt reply. i input LinkList::ListNode * LinkList::find(int index) under the ccp file, however, it returns an error stating that missing 'typename' prior to dependent type name 'LinkList::ListNode'.. (and, any way i can correct this without using auto? ) Thanks – progammingBeignner Sep 16 '14 at 12:46

Using struct as private member to define ListNode within link list class

1 Answers1