linklist class problem

sharkDawg

Hi all,

I have a problem with a code im writing

using Visual studio 2008.

Compiles fine but throws up this when i run it

Unhandled exception at 0x0041222e in OOP-lab7.exe: 0xC0000005: Access violation reading location 0xfeeefeee.

the error happens after the overloaded + operand is used
Edit: should just update this, the error happens the next time i try do anything with the object be in ll.count, ll.max etc

here is the code:

#include "stdafx.h"
#include <iostream>

using namespace std;

class list
{

private:

         struct node
         {
             int data;
            node *link;
         }*p;
public:

         list();
		 ~list();

         void append( int num );
         void del( int num );
         void display();
         int count();
		 int max();
		 int min();
		 int average();
		 void search(int num);

		 friend list  operator+(list &l1, int num); 
         
};

list::list()
{
     p=NULL;
}

list::~list()
{
     node *q;
   if( p == NULL )
        return;

   while( p != NULL )
   {
        q = p->link;
      delete p;
      p = q;
   }
}

void list::append(int num)
{
     node *q,*t;

   if( p == NULL )
   {
        p = new node;
      p->data = num;
      p->link = NULL;
   }
   else
   {
        q = p;
      while( q->link != NULL )
           q = q->link;

      t = new node;
      t->data = num;
      t->link = NULL;
      q->link = t;
   }
}




void list::del( int num )
{
     node *q,*r;
   q = p;
   if( q->data == num )
   {
        p = q->link;
      delete q;
      return;
   }

   r = q;
   while( q!=NULL )
   {
        if( q->data == num )
      {
           r->link = q->link;
         delete q;
         return;
      }

      r = q;
      q = q->link;
   }
   cout<<"\nElement "<<num<<" not Found.";
}

void list::display()
{
     node *q;
   cout<<endl;

   for( q = p ; q != NULL ; q = q->link )
        cout<<endl<<q->data;

}

int list::count()
{
     node *q;
   int c=0;
   for( q=p ; q != NULL ; q = q->link )
        c++;

   return c;
}

int list::max()
{
	node *q;
	int max=0;
	q=p;
	max = q->data;
	for( q ; q != NULL ; q = q->link )
	{
	   if (q->data > max)
	   {
		   max = q->data;

	   }
	}
	    
	return max;
}

int list::min()
{
	int min=0;
	node *q;


	q=p;

	min = q->data;

	
	for( q; q != NULL ; q = q->link )
	{
	   if (q->data < min)
	   {
		   min = q->data;

	   }
	}
	    
	return min;
}
int list::average()
{
	node *q;
	int total=0;

	for( q=p ; q != NULL ; q = q->link )
	{
	   total += q->data;
	}

	total = total/count();
	    
	return total;
}
void list::search(int num)
{
	node *q;
	
	for( q=p; q != NULL ; q = q->link )
	{
	   if (q->data == num)
	   {
		   
			cout<<"\nElement "<<num<<" Found.";

	   }
	}
	return;
}




int main()
{
     list ll;
   cout<<"No. of elements = "<<ll.count();
   ll.append(13);
   ll.append(12);
   ll.append(23);
   ll.append(100);
   ll.append(44);
   ll.append(50);


   ll.display();
   cout<<"\nNo. of elements = "<<ll.count();

   ll.del(333);
   ll.del(12);
   ll.del(98);
   ll = ll + 60;
  // cout<<"\nNo. of elements = "<<ll.count();
	cout<<"\nMax = "<<ll.max();
	cout<<"\nMin = "<<ll.min();
	cout<<"\naverage = "<<ll.average();

	ll.search(50);

   return 0;
}


list  operator+(list &l1, int num)
{

	l1.append(num);

	return l1;
}

Any ideas where the error is coming from?

Thanks for any advice you can give

Beano

you dont seem to have instantiated the class in your main() function.

LARDO

ll = ll + 60; doesnt make any sense.

first of all "ll + 60;" does what u want ie adding 60 to the list but of course this isnt really what the operator + is meant for, the operator + return a list object say b, now u have a = b, but u dont have a copy constructor or overloaded = operator, if these were pointers to objects the statement would work but that causes problems for the + operator then!

also ur operator wont work with statements like ll+ 60 + 70, the secont + call would translate to operator+(60,70); and would fail because u dont have a constructor list(int x);

basically u need some type casting operators a copy constructor an overloaded = operator etc... hope this helps!!

sharkDawg

Lardo your bang on with the copy constructor , a friend of mine figured it out this morning.

Here is the updated code for reference(probably not great but it works! and unfortunately its all the time I have this week to spare on it.)

Note: Apoligies for lack of comments, its a very busy week!

#####################################################*/


#include "stdafx.h"
#include <iostream>

using namespace std;

class list
{

private:

         struct node
         {
             int data;
            node *link;
         }*p;
public:

         list();
		 ~list();
		 list(const list &temp);

         void append( int num );
         void del( int num );
         void display();
		 list &list::operator=(const list &temp);
		 void addList(const list &temp);
         int count();
		 int max();
		 int min();
		 int average();
		 void search(int num);

		 friend list  operator+(const list &l1, int num); 
		 friend list  operator+(list &l1, list&l2);
         
};

list::list()
{
     p=NULL;
}

list::~list()
{
     node *q;
   if( p == NULL )
        return;

   while( p != NULL )
   {
        q = p->link;
      delete p;
      p = q;
   }
}

list::list(const list &temp)
{
	p = NULL;
	for(node *q=temp.p; q != NULL ; q = q->link )
	{
		append(q->data);
	}
}

//function for adding numbers to the list
void list::append(int num)
{
     node *q,*t;

   if( p == NULL )
   {
        p = new node;
      p->data = num;
      p->link = NULL;
   }
   else
   {
        q = p;
      while( q->link != NULL )
	  {
		  q = q->link;
	  }

      t = new node;
      t->data = num;
      t->link = NULL;
      q->link = t;
   }
}



//function for delteting numbers from the list
void list::del( int num )
{
     node *q,*r;
   q = p;
   if( q->data == num )
   {
        p = q->link;
      delete q;
      return;
   }

   r = q;
   while( q!=NULL )
   {
        if( q->data == num )
      {
           r->link = q->link;
         delete q;
         return;
      }

      r = q;
      q = q->link;
   }
  
}

list &list::operator=(const list &temp)
{
	//clean the existing list
	while( p != NULL )
	{
		node *q = p->link;
		delete p;
		p = q;
	}

	//copy the date to the now cean one
	p = NULL;
	for(node *q=temp.p; q != NULL ; q = q->link )
	{
		append(q->data);
	}

	return *this;
}

//function for printing the list
void list::display()
{
     node *q;
   cout<<endl;

   for( q = p ; q != NULL ; q = q->link )
        cout<<endl<<q->data;

}

//function for counting the number of elements in a list
int list::count()
{
     node *q;
   int c=0;
   for( q=p ; q != NULL ; q = q->link )
        c++;

   return c;
}

//function for adding the contents of one list to another
void list::addList(const list &temp)
{
	node *q;
	q =temp.p;
	if( temp.p == NULL )
   {
		cout<<"\nNo numbers found. Returning 0";
		return;
	}

	
	for( q; q != NULL ; q = q->link )
	{
	   append(q->data);
	}
  
}

//function for finding the largest number in a list
int list::max()
{
	
	node *q;
	int max=0;
	q=p;
	if( p == NULL )
   {
		cout<<"\nNo numbers found. Returning 0";
		return 0;
	}
	max = q->data;
	for( q ; q != NULL ; q = q->link )
	{
	   if (q->data > max)
	   {
		   max = q->data;

	   }
	}
	    
	return max;
}

//function for finding the smallest number in a list
int list::min()
{
	int min=0;
	node *q;


	q=p;

	if( p == NULL )
   {
		cout<<"\nNo numbers found. Returning 0";
		return 0;
	}

	min = q->data;

	
	for( q; q != NULL ; q = q->link )
	{
	   if (q->data < min)
	   {
		   min = q->data;

	   }
	}
	    
	return min;
}

//function for finding the average of the numbers in the list
int list::average()
{
	node *q;
	int total=0;
	q=p;
	if( p == NULL )
   {
		cout<<"\nNo numbers found. Returning 0";
		return 0;
	}

	for( q=p ; q != NULL ; q = q->link )
	{
	   total += q->data;
	}

	total = total/count();
	    
	return total;
}

//function for searching for a certain value in the list
void list::search(int num)
{
	node *q;
	
	for( q=p; q != NULL ; q = q->link )
	{
	   if (q->data == num)
	   {
		   
			cout<<"\nElement "<<num<<" Found.";

	   }
	}
	return;
}






int main()
{
	list ll;
	list l2;
	 
	cout<<"No. of elements = "<<ll.count();

	ll.append(13);
	ll.append(12);
	ll.append(23);

	cout<<"\nPrinting contents of ll"<<endl;

	ll.display();

	l2.append(100);
	l2.append(44);
	l2.append(50);

	cout<<"\nPrinting contents of l2"<<endl;

	l2.display();

	cout<<"\nAdding contents of l2 to ll"<<endl;

	ll = ll + l2;

	ll.display();

	cout<<"\nNo. of elements = "<<ll.count();


	cout<<"\nAdding 60 to ll"<<endl;
	ll = ll + 60;
	ll.display();

	cout<<"\nMax = "<<ll.max();
	cout<<"\nMin = "<<ll.min();
	cout<<"\naverage = "<<ll.average();

	cout<<"\nSearching for 50"<<endl;
	ll.search(50);


	return 0;
}


list  operator+(list &l1, list&l2)
{
	list result = l1;
	result.addList(l2);

	return result;
}

list operator+(const list &l1, int num)
{
	list result = l1;
	result.append(num);

	return result;
}

LARDO

for what its worth dude i would change append to list ,
ie list::list instead of list::append, i think the logic would read better and u
have a new constructor into the bargain which would prevent errors in certain contexts. After all append should add an existing object to the list end not create a new object. Object creation should be done in constructors.