c++ access violation with classes [closed] - c++

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Hi I am getting an access violation reading error in my linked list header file. The project takes a binary tree and turns it into an ordered linked list. the binary tree header:
#ifndef BINARY_SEARCH_TREE_H
#define BINARY_SEARCH_TREE_H
#include "dsexceptions.h"
#include "LinkedList.h"
#include <iostream>
using namespace std;
template <typename Comparable>
class BinarySearchTree
{
public:
BinarySearchTree( ) :root( NULL )
{ }
BinarySearchTree(const BinarySearchTree & rhs) : root(NULL)
{ *this = rhs; }
~BinarySearchTree( )
{ makeEmpty( ); }
const Comparable & findMin( ) const
{
if (isEmpty( ))
throw UnderflowException( );
return findMin(root)->element;
}
const Comparable & findMax( ) const
{
if(isEmpty( ))
throw UnderflowException( );
return findMax( root )->element;
}
bool contains(const Comparable & x) const
{ return contains(x, root); }
bool isEmpty( ) const
{ return root == NULL; }
void printTree(ostream & out = cout)
{
if (isEmpty( ))
out << "Empty tree" << endl;
else
printTree(root, out);
}
void makeEmpty( )
{ makeEmpty(root); }
void insert(const Comparable & x)
{ insert(x, root); }
void remove(const Comparable & x)
{ remove(x, root); }
const BinarySearchTree & operator=(const BinarySearchTree & rhs)
{
if (this != &rhs)
{
makeEmpty( );
root = clone(rhs.root);
}
return *this;
}
void toList(linkedlist l)
{ toList(l, root); }
private:
struct BinaryNode
{
Comparable element;
BinaryNode *left;
BinaryNode *right;
BinaryNode(const Comparable & theElement, BinaryNode *lt, BinaryNode *rt)
: element(theElement), left(lt), right(rt) { }
};
BinaryNode *root;
void toList(linkedlist l, BinaryNode *&t)
{
if(t==NULL)
{ return; }
toList(l,t->left);
l.add(t->element);
toList(l,t->right);
}
void printTree(BinaryNode *&t, ostream & out = cout)
{
if(t==NULL)
{ return; }
printTree(t->left,out);
cout << t->element << endl;
printTree(t->right,out);
}
void insert(const Comparable & x, BinaryNode * & t)
{
if (t == NULL)
t = new BinaryNode(x, NULL, NULL);
else if (x < t->element)
insert(x, t->left);
else if (t->element < x)
insert(x, t->right);
else; // Duplicate; do nothing
}
void remove(const Comparable & x, BinaryNode * & t)
{
if (t == NULL)
return; // Item not found; do nothing
if (x < t->element)
remove(x, t->left);
else if (t->element < x)
remove(x, t->right);
else if (t->left != NULL && t->right != NULL) // Two children
{
t->element = findMin(t->right)->element;
remove(t->element, t->right);
}
else
{
BinaryNode *oldNode = t;
t = (t->left != NULL) ? t->left : t->right;
delete oldNode;
}
}
BinaryNode * findMin(BinaryNode *t) const
{
if (t == NULL)
return NULL;
if (t->left == NULL)
return t;
return findMin(t->left);
}
BinaryNode * findMax(BinaryNode *t) const
{
if (t != NULL)
while (t->right != NULL)
t = t->right;
return t;
}
bool contains(const Comparable & x, BinaryNode *t) const
{
if (t == NULL)
return false;
else if (x < t->element)
return contains(x, t->left);
else if (t->element < x)
return contains(x, t->right);
else
return true; // Match
}
void makeEmpty(BinaryNode * & t)
{
if (t != NULL)
{
makeEmpty(t->left);
makeEmpty(t->right);
delete t;
}
t = NULL;
}
BinaryNode * clone(BinaryNode *t) const
{
if (t == NULL)
return NULL;
else
return new BinaryNode(t->element, clone(t->left), clone(t->right));
}
};
#endif
the linked list header:
#ifndef LINKED_LIST_H
#define LINKED_LIST_H
#include <iostream>
using namespace std;
class linkedlist
{
private:
struct lNode{
int data;
lNode *next;
};
struct lNode *head;
public:
linkedlist()
{ struct lNode *head = new lNode;
head->next = NULL;
}
void add(int n) {
lNode *newlNode = new lNode;
newlNode->data = n;
newlNode->next = NULL;
lNode *cur = head;
while(true) {
if(cur->next == NULL)
{
cur->next = newlNode;
break;
}
cur = cur->next;
}
}
void display() {
lNode *list = head;
while(true)
{
if (list->next == NULL)
{
cout << list->data << endl;
break;
}
cout << list->data << endl;
list = list->next;
}
cout << "done" << endl;
}
};
#endif
the main cpp file:
#include <iostream>
#include "BinarySearchTree.h"
#include "LinkedList.h"
using namespace std;
int main( )
{
BinarySearchTree<int> t;
linkedlist l;
int i;
cout << "inserting nodes into tree" << endl;
t.insert(50);
t.insert(60);
t.insert(30);
t.insert(20);
t.insert(40);
t.insert(70);
t.insert(55);
t.insert(65);
t.insert(25);
t.insert(35);
t.insert(85);
t.insert(100);
t.insert(15);
t.insert(45);
t.insert(95);
t.insert(105);
t.insert(10);
t.insert(75);
t.insert(110);
t.insert(12);
t.insert(92);
t.insert(32);
t.insert(82);
t.insert(22);
t.insert(32);
t.printTree( );
t.toList(l);
cout << "Finished processing" << endl;
l.display();
return 0;
}
The location of the error is in the linked list header file here: if(cur->next == NULL). I do not see how it could be an access error as everything is contained inside that class.

Answer 1

In the code above you have this section of code:
struct lNode *head;
public:
linkedlist()
{ struct lNode *head = new lNode;
head->next = NULL;
}
That code is defining two instances of the head node which I'm sure is not what you want.
The ctor should be something more like this:
linkedlist()
{
head = new lNode;
head->next = NULL;
}

Answer 2

Your code does not test for the empty list -- that is where there are no elements in the list and the head is NULL.
Also, you are missing any constructors which is initializing the class, so it may very well be that head has an undefined value -- also there add method make not use of the loop, or make any recording of the added elements...
So in short, there are a lot of programming issues to fix.