trying to implement stack using class template

**progmateur** · 12-05-2013

I am getting errors...please rectify my code or atleast point out where I am wrong

Code:

#include <iostream>#include <conio.h>


using namespace std;


template <class T>
class NODE
{
      friend class STACK;
      private:
              
      T DATA;
      NODE<T> *LINK;
       
      };
      
 template <class T>     
 class STACK
 {
       private:               
              NODE<T> *TOP;
       public:
              STACK(){TOP=NULL;}
              STACK<T> &PUSH(T x);
              STACK<T> &POP(T *x);
              void Display();      
       
       };


 template <class T>      
STACK<T> &STACK<T>::PUSH(T x)
{
      NODE<T> *NEW=new NODE<T>;
      NEW->DATA=x;
      NEW->LINK=TOP;
      TOP=NEW;      
      return *this;
      
      }


template <class T>      
STACK<T> &STACK<T>::POP(T *x)
{
      NODE<T> *DEL=TOP;
      *x=DEL->DATA;
      TOP=TOP->LINK;
      delete DEL;
      return *this;
      }
      
template <class T>      
void STACK<T>::Display()
{
     NODE<T> *PTR=TOP;
     while(PTR!=NULL)
                     {
                     cout<<PTR->DATA<<endl;
                     PTR=PTR->LINK;                
                     }
     }
     
     




int main()
    {
    STACK<int> S;
    int s;
    S.PUSH(45);
    S.PUSH(76);
    S.PUSH(44);
    S.PUSH(23);
    S.POP(&s);
    cout<<"popped data : "<<s<<endl;        
    S.Display();    
    getch();
    return 0;
         }

**tabstop** · 12-05-2013

I guess you have the title right this time. I'll repost:
"If you are getting errors, you could at least bother to say what they are in the post.
(EDIT: Although I do note that you don't bother to check whether anything exists on the stack before you (try to) pop a value off.)"

**laserlight** · 12-05-2013

Have you tried implementing your last two class templates as non-templates, e.g., assume that T is int and simply don't involve templates until your code is correct.

**progmateur** · 12-05-2013

yes I did heres the code

Code:

#include <iostream>#include <conio.h>


using namespace std;


class NODE
{
      friend class STACK;
      private:
              
      int DATA;
      NODE *LINK;
       
      };
 class STACK
 {
       private:               
              NODE *TOP;
       public:
              STACK(){TOP=NULL;}
              STACK &PUSH(int x);
              STACK &POP(int *x);
              void Display();      
       
       };
       
STACK& STACK::PUSH(int x)
{
      NODE *NEW=new NODE;
      NEW->DATA=x;
      NEW->LINK=TOP;
      TOP=NEW;      
      return *this;
      
      }
      
STACK &STACK::POP(int *x)
{
      NODE *DEL=TOP;
      *x=DEL->DATA;
      TOP=TOP->LINK;
      delete DEL;
      return *this;
      }
void STACK::Display()
{
     NODE *PTR=TOP;
     while(PTR!=NULL)
                     {
                     cout<<PTR->DATA<<endl;
                     PTR=PTR->LINK;                
                     }
     
     }
     
     
int main()
    {
    STACK S;
    int s;
    S.PUSH(45);
    S.PUSH(76);
    S.PUSH(44);
    S.PUSH(23);
    S.POP(&s);
    cout<<"popped data : "<<s<<endl;        
    S.Display();    
    
    getch();
    return 0;
         }

**progmateur** · 12-05-2013

Originally Posted by tabstop

I guess you have the title right this time. I'll repost:
"If you are getting errors, you could at least bother to say what they are in the post.
(EDIT: Although I do note that you don't bother to check whether anything exists on the stack before you (try to) pop a value off.)"

just trying a straightforward implementation...later Ill modify my code as per my requirement thank you

**laserlight** · 12-05-2013

So, does your code work? If not, how does it not work?

**progmateur** · 12-05-2013

Originally Posted by laserlight

So, does your code work? If not, how does it not work?

It didnt work.........

errors:

In instantiation of `NODE<int>':
34 instantiated from `STACK<T>& STACK<T>::PUSH(T) [with T = int]'
66 instantiated from here
8 template argument required for `struct STACK'
12 `int NODE<int>:: DATA' is private

and more....

**tabstop** · 12-05-2013

So when we say post the errors, why not ... post the errors?

Code:

tabstop@ubuntu:~/helping$ g++ -Wall -o stack stack.cpp
stack.cpp: In function ‘int main()’:
stack.cpp:81:11: error: ‘getch’ was not declared in this scope
stack.cpp: At global scope:
stack.cpp: In instantiation of ‘NODE<int>’:
stack.cpp:35:22:   instantiated from ‘STACK<T>& STACK<T>::PUSH(T) [with T = int]’
stack.cpp:74:14:   instantiated from here
stack.cpp:9:1: error: template argument required for ‘struct STACK’
stack.cpp: In member function ‘STACK<T>& STACK<T>::PUSH(T) [with T = int]’:
stack.cpp:74:14:   instantiated from here
stack.cpp:13:7: error: ‘int NODE<int>::DATA’ is private
stack.cpp:36:5: error: within this context
stack.cpp:14:14: error: ‘NODE<int>* NODE<int>::LINK’ is private
stack.cpp:37:5: error: within this context
stack.cpp: In member function ‘STACK<T>& STACK<T>::POP(T*) [with T = int]’:
stack.cpp:78:13:   instantiated from here
stack.cpp:13:7: error: ‘int NODE<int>::DATA’ is private
stack.cpp:48:5: error: within this context
stack.cpp:14:14: error: ‘NODE<int>* NODE<int>::LINK’ is private
stack.cpp:49:5: error: within this context
stack.cpp: In member function ‘void STACK<T>::Display() [with T = int]’:
stack.cpp:80:15:   instantiated from here
stack.cpp:13:7: error: ‘int NODE<int>::DATA’ is private
stack.cpp:60:9: error: within this context
stack.cpp:14:14: error: ‘NODE<int>* NODE<int>::LINK’ is private
stack.cpp:61:9: error: within this context

The big one is probably this one:
stack.cpp:9:1: error: template argument required for ‘struct STACK’
as you have tried to declare STACK (by itself) as a friend of NODE<T>. You can forward declare the STACK class and then declare STACK<T> as a friend. (The "right" way to do it is for the NODE class to provide methods to access and set those variables, of course.)

**laserlight** · 12-05-2013

By the way, stop fully capitalising your class and member names. Fully capitalised names are conventionally reserved for macros and constants.

**progmateur** · 12-05-2013

Originally Posted by tabstop

So when we say post the errors, why not ... post the errors?

Code:

tabstop@ubuntu:~/helping$ g++ -Wall -o stack stack.cpp
stack.cpp: In function ‘int main()’:
stack.cpp:81:11: error: ‘getch’ was not declared in this scope
stack.cpp: At global scope:
stack.cpp: In instantiation of ‘NODE<int>’:
stack.cpp:35:22:   instantiated from ‘STACK<T>& STACK<T>::PUSH(T) [with T = int]’
stack.cpp:74:14:   instantiated from here
stack.cpp:9:1: error: template argument required for ‘struct STACK’
stack.cpp: In member function ‘STACK<T>& STACK<T>::PUSH(T) [with T = int]’:
stack.cpp:74:14:   instantiated from here
stack.cpp:13:7: error: ‘int NODE<int>::DATA’ is private
stack.cpp:36:5: error: within this context
stack.cpp:14:14: error: ‘NODE<int>* NODE<int>::LINK’ is private
stack.cpp:37:5: error: within this context
stack.cpp: In member function ‘STACK<T>& STACK<T>::POP(T*) [with T = int]’:
stack.cpp:78:13:   instantiated from here
stack.cpp:13:7: error: ‘int NODE<int>::DATA’ is private
stack.cpp:48:5: error: within this context
stack.cpp:14:14: error: ‘NODE<int>* NODE<int>::LINK’ is private
stack.cpp:49:5: error: within this context
stack.cpp: In member function ‘void STACK<T>::Display() [with T = int]’:
stack.cpp:80:15:   instantiated from here
stack.cpp:13:7: error: ‘int NODE<int>::DATA’ is private
stack.cpp:60:9: error: within this context
stack.cpp:14:14: error: ‘NODE<int>* NODE<int>::LINK’ is private
stack.cpp:61:9: error: within this context

The big one is probably this one:
stack.cpp:9:1: error: template argument required for ‘struct STACK’
as you have tried to declare STACK (by itself) as a friend of NODE<T>. You can forward declare the STACK class and then declare STACK<T> as a friend. (The "right" way to do it is for the NODE class to provide methods to access and set those variables, of course.)

I would be greatful to you if you ellaborate...I am new to c++.. a block of code as an example will help

**tabstop** · 12-05-2013

Remember this is just a hack until you write a proper node class.

Code:

template <class T> class STACK; //forward declare STACK as a templated class

/* ... then in your NODE class ... */
friend class STACK<T>;

**laserlight** · 12-05-2013

Originally Posted by progmateur

I would be greatful to you if you ellaborate...I am new to c++.. a block of code as an example will help

For starters, you need to rename what I suggested and format your code properly, e.g.,

Code:

#include <iostream>

template <class T>
class Stack;

template <class T>
class Node
{
    friend class Stack<T>;
private:

    T data;
    Node<T>* link;
};

template <class T>
class Stack
{
private:
    Node<T>* top;
public:
    Stack() : top(NULL) {}
    Stack<T>& push(T x);
    Stack<T>& pop(T* x);
    void display(std::ostream& out);
};

template <class T>
Stack<T>& Stack<T>::push(T x)
{
    Node<T>* new_node = new Node<T>;
    new_node->data = x;
    new_node->link = top;
    top = new_node;
    return *this;
}

template <class T>
Stack<T>& Stack<T>::pop(T* x)
{
    Node<T>* delete_node = top;
    *x = delete_node->data;
    top = top->link;
    delete delete_node;
    return *this;
}

template <class T>
void Stack<T>::display(std::ostream& out)
{
    Node<T>* node = top;
    while (node != NULL)
    {
        out << node->data << std::endl;
        node = node->link;
    }
}

int main()
{
    using namespace std;

    Stack<int> stack_obj;
    int value;
    stack_obj.push(45);
    stack_obj.push(76);
    stack_obj.push(44);
    stack_obj.push(23);
    stack_obj.pop(&value);
    cout << "popped data : " << value <<endl;
    stack_obj.display(cout);
    return 0;
}

I have taken the liberty of adding the fix that you're looking for, i.e., the forward declaration of the Stack class template and then the change in the friend class declaration. Furthermore, I have changed the display member function to take an argument, and moved the using directive to within the main function: you shouldn't have a using directive at file scope before a class definition as the class definition will almost certainly be moved to a header file if you do ever have one.

By the way, have you ever seen the std::stack container adapter interface?

**progmateur** · 12-05-2013

Originally Posted by laserlight

For starters, you need to rename what I suggested and format your code properly, e.g.,

Code:

#include <iostream>

template <class T>
class Stack;

template <class T>
class Node
{
    friend class Stack<T>;
private:

    T data;
    Node<T>* link;
};

template <class T>
class Stack
{
private:
    Node<T>* top;
public:
    Stack() : top(NULL) {}
    Stack<T>& push(T x);
    Stack<T>& pop(T* x);
    void display(std::ostream& out);
};

template <class T>
Stack<T>& Stack<T>::push(T x)
{
    Node<T>* new_node = new Node<T>;
    new_node->data = x;
    new_node->link = top;
    top = new_node;
    return *this;
}

template <class T>
Stack<T>& Stack<T>::pop(T* x)
{
    Node<T>* delete_node = top;
    *x = delete_node->data;
    top = top->link;
    delete delete_node;
    return *this;
}

template <class T>
void Stack<T>::display(std::ostream& out)
{
    Node<T>* node = top;
    while (node != NULL)
    {
        out << node->data << std::endl;
        node = node->link;
    }
}

int main()
{
    using namespace std;

    Stack<int> stack_obj;
    int value;
    stack_obj.push(45);
    stack_obj.push(76);
    stack_obj.push(44);
    stack_obj.push(23);
    stack_obj.pop(&value);
    cout << "popped data : " << value <<endl;
    stack_obj.display(cout);
    return 0;
}

I have taken the liberty of adding the fix that you're looking for, i.e., the forward declaration of the Stack class template and then the change in the friend class declaration. Furthermore, I have changed the display member function to take an argument, and moved the using directive to within the main function: you shouldn't have a using directive at file scope before a class definition as the class definition will almost certainly be moved to a header file if you do ever have one.

By the way, have you ever seen the std::stack container adapter interface?

very kind of you...now I understand the meaning of forward declaration!

**jocdrew21** · 12-06-2013

I really like how this site allows us new guys to read so much code and see how others think. However I was wondering what is the advantage to writing it like this then lets say using one Class and one Struct which seems easier to read.

Just was wondering..

**tabstop** · 12-06-2013

Originally Posted by jocdrew21

I really like how this site allows us new guys to read so much code and see how others think. However I was wondering what is the advantage to writing it like this then lets say using one Class and one Struct which seems easier to read.

Just was wondering..

A struct is a class (more or less, with some restrictions), so there isn't a difference, let alone an advantage.

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