Inheritance with pointers:Overloading?

i derived a class from a linklist class. the problem is i can't access the next or previous pointers.type mismatch.do anybody have an idea how to solve it? should i overload the base class pointers, and how should i go about it?
the program follows.i tried to make it as small as possible so please bear with me!!

Code:

---

#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
#include <stdio.h>
#include <iostream.h>
#include <dos.h>

//class definition of link list
class LLClass
  {
  protected:
    class LLClass *next;                        //pointer to next position
    class LLClass *prev;                        //pointer to previous position



  public:
    LLClass();
    ~LLClass();
    void setnext(class LLClass *temp);
    void setprev(class LLClass *temp);

    virtual class LLClass *getnext();
    virtual class LLClass *getprev();

  };
  LLClass::LLClass()
  {};

  LLClass::~LLClass()
  {}

void LLClass::setnext(class LLClass *temp)
  {
  next=temp;
  }//setnext

  void LLClass::setprev(class LLClass *temp)
  {
  prev=temp;
  }//setprev

  class LLClass *LLClass::getnext()
  {
  return next;
  }//getnext

  class LLClass *LLClass::getprev()
  {
  return prev;
  }//getprev

//class definition for class point
class Point
  {
  private:
    int x,y;                          //top left corner
    int color;                                //color of the box
    int direction;                        //direction the rectangle is going


  public:
    Point();
    ~Point();

    int xx,yy;                                //public coordinates
    int chcolor;                        //change in the color
    int dir;                          //the direction of the box

    void setvalues(int xx, int yy);      //get values for x,y
    void setcolor(int chcolor);          //change the color
    void setdir(int dir);                //change the direction

    int getx();
    int gety();
    int getcolor();
    int getdir();

    int inccolor();
    int deccolor();
    int incx();
    int decx();
    int incy();
    int decy();
  };
  Point::Point()
 {
  x=y=0;                                //default box at 0
  direction=0;                                //default direction at 0
  color=2;                                //default color green
 }//cnstrctr
 Point::~Point()
  {}

 void Point::setvalues(int xx, int yy)
 {
  x=xx;
  y=yy;
 }//setvalues

 void Point::setcolor(int chcolor)
{
 color=chcolor;
}//setcolor

void Point::setdir(int dir)
{
 direction=dir;
}//setdir

int Point::getx()
{
 return x;
}//getx

int Point::gety()
{
 return y;
}//gety

int Point::getcolor()
{
 return color;
}//getcolor

int Point::getdir()
{
 return direction;
}//getdir

int Point::inccolor()
{
 color++;
 return color;
}//inccolor

int Point::deccolor()
{
 color--;
 return color;
}//deccolor

int Point::incy()
{
 y++;
 return y;
}//incy

int Point::decy()
{
 y--;
 return y;
}//decy

int Point::incx()
{
 x++;
 return x;
}//incx

int Point::decx()
{
 x--;
 return x;
}//decx

//class definition of rectangle
class Rectangle:public LLClass,public Point
  {
  private:
    int b,t;


  public:
    Rectangle();                                //constructor
    ~Rectangle();                                //destructor
    class Rectangle *newptr,*first,*last,*curr;//pointers

    //functions in class
    void setrnext(class LLClass *temp);
    class LLClass *convnext(class LLClass *temp);
    class Rectangle *getrnext();                        //next pointer


    class LLClass *getnext();                        //next pointer
    class LLClass *getprev();                        //prev pointer
  };
  Rectangle::Rectangle()
  {}//cnstrctr

  Rectangle::~Rectangle()
  {}

  class LLClass *Rectangle::getnext()
  {
  return next;
  }//getnext

  class LLClass *Rectangle::getprev()
  {
  return prev;
  }//getprev

int main(int argc,char *argv[])
{
  class Rectangle *first,*last,*curr, *newptr, *temp;
  class LLClass *temp;
  int rct,choice;


  //auto detection
  int gdriver = 0, gmode, errorcode;

  //initialize graphics
  initgraph(&gdriver, &gmode, "c:\\tc\\bgi\\");


  //result of initialization
  errorcode = graphresult();

  if (errorcode != grOk)
  {
      printf("Graphics error: %s\n", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();
      exit(1);
  }
  //get the number of objects
  rct=atoi(argv[1]);


  //create first box
  randomize();
  first=curr=newptr=new Rectangle;
  first->setvalues(20+rand()%600,20+rand()%430);



  for(int b=1;b<=rct-1;b++)
  {
    newptr=new Rectangle;
    newptr->setvalues(20+rand()%600,20+rand()%430);


    //linking
    newptr->setprev(curr);
    curr->setnext(newptr);
    curr=newptr;
  }//end of new box (fr)
  newptr->setnext(first);
  last=newptr;
  first->setprev(newptr);

  //draw outerbox
  choice=0;
  rectangle(1,1,630,470);


  //problem starts here
  //the linklist was created and data was written to it but i can't access it
  //draw the small boxes
  curr=first;
  setcolor(15);
  cout<<endl;
  for (int j=1;j<=rct;j++)
  {
    temp=curr->getnext();
    curr=curr->getnext();
    cout<<newptr->getprev()<<"  ";
    cout<<newptr->getnext()<<endl;
  }//fr

 getch();
 closegraph();
 argc=argc;
 choice=choice;
 last=last;
 return 0;
}

---

if some one can help via e-mail or thread please do.thx

why not have methods to return the pointers you want.. and i dint got hrough your code.. how abt you post only the parts required removing all the unnecessary stuff.

what methods?
i don't know what methods there are!
i could post a smaller program:#include <stdio.h>
#include <conio.h>
#include <stdio.h>
#include <iostream.h>
#include <dos.h>

//class definition of link list
class LLClass
{
protected:
class LLClass *next; //pointer to next position
class LLClass *prev; //pointer to previous position



public:
LLClass();
~LLClass();
void setnext(class LLClass *temp);
void setprev(class LLClass *temp);

class LLClass* getnext();
class LLClass* getprev();

};
LLClass::LLClass()
{};

LLClass::~LLClass()
{}

void LLClass::setnext(class LLClass *temp)
{
next=temp;
}//setnext

void LLClass::setprev(class LLClass *temp)
{
prev=temp;
}//setprev

class LLClass *LLClass::getnext()
{
return next;
}//getnext

class LLClass *LLClass::getprev()
{
return prev;
}//getprev

//class definition for class point
class Point
{
private:
int x,y; //top left corner
int color; //color of the box
int direction; //direction the rectangle is going


public:
Point();
~Point();

int xx,yy; //public coordinates
int chcolor; //change in the color
int dir; //the direction of the box

void setvalues(int xx, int yy); //get values for x,y
void setcolor(int chcolor); //change the color
void setdir(int dir); //change the direction

int getx();
int gety();
int getcolor();
int getdir();

int inccolor();
int deccolor();
int incx();
int decx();
int incy();
int decy();
};

//no problem with this implementation
//class definition of rectangle
class Rectangle:public LLClass,public Point
{
private:
int b,t;



public:
Rectangle(); //constructor
~Rectangle(); //destructor

//functions in class


};
Rectangle::Rectangle()
{}//cnstrctr

Rectangle::~Rectangle()
{}



int main(int argc,char *argv[])
{
class Rectangle *first,*last,*curr, *newptr, *temp;
int rct,choice;



//create first box
randomize();
first=curr=newptr=new Rectangle;
first->setvalues(20+rand()%600,20+rand()%430);



for(int b=1;b<=rct-1;b++)
{
newptr=new Rectangle;
newptr->setvalues(20+rand()%600,20+rand()%430);


//linking
newptr->setprev(curr);
curr->setnext(newptr);
curr=newptr;
}//end of new box (fr)
newptr->setnext(first);
last=newptr;
first->setprev(newptr);


//draw outerbox
choice=0;
rectangle(1,1,630,470);


//problem starts here
//the linklist was created and data was written to it but i can't access it
//draw the small boxes
curr=first;
setcolor(15);
cout<<endl;
for (int j=1;j<=rct;j++)
{
cout<<curr->getx()<<" ";
cout<<curr->gety()<<endl;
//?????????????????????
curr=curr->getnext();
}//fr

getch();
return 0;
}

Hi katie,

reading your (rather messy) code bearing in mind the error reported by your compiler "type mismatch" I can mention the line

Code:

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curr=curr->getnext() ;

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in

Code:

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int main(int argc,char *argv[])

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as one source of trouble; assigning a base class pointer (LLClass*) to a derived class pointer (Rectangle*); there's no such implicit conversion. If you can afford a guarantee that a base class pointer already points to a derived class object, brute force, that is static type casting, may help. However, it is tasteless.

This, and similar errors, are IMHO indicators of bad design.
Ask yourself is it really necessary to have both public data and examinig/modifying member functions in class Point ? Is it correct to couple concepts such as "linked list", "rectangle" and "point" together in one component ?
Pay attention to cleaner design.

Regardless, try not to reinvent the wheel; use standard <list>.

-strontium90