Question

I have a .h file with this in it:

#ifndef CS240_LINKED_LIST_H
#define CS240_LINKED_LIST_H

#include <string>

//! LLNode implements a doubly-linked list node
class LLNode {
        friend class LinkedList;
    public:
    
        LLNode(const std::string & v, LLNode * p, LLNode * n) :
          value(v), prev(p), next(n)
        {
        }
    
    private:
        std::string value;        //!< value stored in the node
        LLNode * prev;            //!< pointer to previous node in the list
        LLNode * next;            //!< pointer to next node in the list
};


//! LinkedList implements a doubly-linked list
class LinkedList
{
    public:
    
        //!  No-arg constructor.  Initializes an empty linked list
        LinkedList();
    
    
        //!  Copy constructor.  Makes a complete copy of its argument
        LinkedList(const LinkedList & other);
    
    private:
        //!  two dummy nodes to keep track of the beginning and end of the list.
        LLnode beginning;
        LLnode end;
        int size;
};

#endif

In a cpp file I have:

#include "LinkedList.h"

LinkedList::LinkedList(){
    this->beginning.prev = NULL;
    this->beginning.next = this->end;
    this->end.prev = this->beginning;
    this->end.next = NULL;
}

Here’s the output:

>g++ -o LinkedList.o LinkedList.cpp
In file included from LinkedList.cpp:1:
LinkedList.h:37: error: 'LLnode' does not name a type
LinkedList.h:38: error: 'LLnode' does not name a type
LinkedList.cpp: In constructor 'LinkedList::LinkedList()':
LinkedList.cpp:4: error: 'class LinkedList' has no member named 'beginning'
LinkedList.cpp:5: error: 'class LinkedList' has no member named 'beginning'
LinkedList.cpp:5: error: 'class LinkedList' has no member named 'end'
LinkedList.cpp:6: error: 'class LinkedList' has no member named 'end'
LinkedList.cpp:6: error: 'class LinkedList' has no member named 'beginning'
LinkedList.cpp:7: error: 'class LinkedList' has no member named 'end'

I don’t know how to fix this. How else would I set the beginning and end objects? Just so you know, I’m a Java programmer learning C++.

Answer 1

• You have misspelt LLNode as LLnode.
• You need to add a default constructor to the LLNode class
• you need to take the address of the this->beginning and this->end members in the LinkedList constructor:

.

LinkedList::LinkedList(){
    this->beginning.prev = NULL;
    this->beginning.next = &this->end;
    this->end.prev = &this->beginning;
    this->end.next = NULL;
}