Thread: trouble with template comparision

I have a problem with this code. How can i call the compare function to compare 2 different types !!! It gives me an error message:

Main.cpp
(23): error C2664: 'Stack<int>::compare' : cannot convert parameter 1 from 'Stack<StackElement>' to 'Stack<StackElement>'
with
[
StackElement=char
]
and
[
StackElement=int
]




Stack.h:
======

Code:

#ifndef STACK
#define STACK

const int STACK_CAPACITY=128;
#include<assert.h>

template<typename StackElement>
class Stack
{
public:
   Stack();
   bool empty() const;
   void push(const StackElement&);
   void display() const;
   StackElement top() const;
   void pop();
   bool compare(Stack<StackElement> S1, Stack<StackElement> S2);
   //bool compare(Stack<StackElement> S1);
   friend ostream& operator <<(ostream&, const Stack<StackElement>&);
private:
   StackElement myArray[STACK_CAPACITY];
   int myTop;
};
template<typename StackElement>
Stack<StackElement>::Stack()
{
	myTop=-1;
}

template<typename StackElement>
bool Stack<StackElement>::empty() const
{
	return (myTop==-1);
}

template<typename StackElement>
void Stack<StackElement>::push( const StackElement& value)
{
 	if (myTop<STACK_CAPACITY-1)
	{
		++myTop;
		myArray[myTop]=value;
	}
	else
	cerr<<"*** Stack is full---can't add new vale***\n";
}
template<typename StackElement>
void Stack<StackElement>::display() const
{
 	for (int i=myTop;i>=0;i--)
	cout<<myArray[i]<<endl;
}

template<typename StackElement>
StackElement Stack<StackElement>::top() const
{
	assert (!empty());
	return myArray[myTop];
}

template<typename StackElement>
void Stack<StackElement>::pop()
{
	if (myTop>=0)
		myTop--;
	else
	cerr<<"*** Stack is empty--can't remove a value ***\n";
}

template<typename StackElement>
ostream& operator<<(ostream& out, const Stack<StackElement> & st)
{
	for(int pos=st.myTop; pos>=0; pos--)
		out<<st.myArray[pos]<<endl;
	return out;
}

template<typename StackElement>
bool Stack<StackElement>::compare(Stack<StackElement> S1, Stack<StackElement> S2)
{

	// code to compare the two array types

 	return 0;
}

#endif

Main.cpp:
=======

Code:

#include<iostream>
using namespace std;
#include"Stack.h"

int main()
{
	Stack<int> s1;
	Stack<char> s2;
	
	char str[]="ABCDEFG";
	
	for(int i=0;i<4;i++) s1.push(i);
	
	cout<<"Stack s1 contents\n";
	s1.display();
	cout<<"Stack s1 Top value: "<<s1.top();
	
	for(i=0;i<4;i++) s2.push(str[i]);
	cout<<"\n\nStack s2 contents\n";
	s2.display();
	cout<<"Stack s2 Top value: "<<s2.top()<<endl<<endl;

	s1.compare(s1,s2);

	cout<<s1<<s2;


	cout<<endl;

	return 0;
}

Here is one way:

Code:

template<typename T1, typename T2>
bool operator==(const Stack<T1> &s1, const Stack<T2> &s2)
{
    // Compare s1 and s2
    return true;
}

Another possibility is to have a templated member function of the Stack<> class, but your compiler may not like it. VC++ 6.0 is ok with it as long as the implementation stays within the class declaration.

Code:

template<typename StackElement>
class Stack
{
public:
    //...
    template<typename T2>
    bool compare(const Stack<T2> &s)
    {
        // Compare *this with s
        return true;
    }
    //...
};

The only issue with both of these is that you will not have access to private members of a passed in Stack<> class. This is because Stack<int> and Stack<char> are two physically different classes, and therefore one can't access the other's privates.

gg