Перегрузка cout.operator<<

#include <iostream>
#include <cstdlib>
#include <exception>
using namespace std;
 
template <typename T>
class Stack
{
public:
    class Bad_index: public exception
    {
    public:
        Bad_index(const char* pch): exception(pch) {}
    };
private:
    enum {MAX = 10};
    const int SIZE;
    T* p;
    int top;
    Stack& operator==(const Stack& s) {return *this;}
public:
    explicit Stack(int sz = MAX): SIZE(sz), top(0), p(new T[SIZE]) {}
    Stack(const Stack& s);
    ~Stack() {delete [] p;}
    bool isfull(){return top==SIZE;}
    bool isempty(){return top==0;}
    T& pop();
    void push(const T& t);
    friend ostream& operator<<(ostream& os, Stack<T>& s);
};
template <typename T>
Stack<T>::Stack(const Stack& s): SIZE(s.SIZE), top(s.top), p(new T[SIZE])
{
    for (register int i=0; i<top; ++i)
        p[i] = s.p[i];
}
template <typename T>
T& Stack<T>::pop()
{
    if (isempty())
        throw Bad_index("Exception. Stack is empty.");
    return p[--top];    
}
template <typename T>
void Stack<T>::push(const T& t)
{
    if (isfull())
        throw Bad_index("Exception. Stack is full.");
    p[top++] = t;
}
template <typename T>
ostream& operator<<(ostream& os, Stack<T>& s)
{
    if (s.isempty())
        cout << "Stack is empty.";
    else
        for (register int i=0; i<s.top; ++i)
            os << s.p[i] << " ";
    return os;
}
 
int main()
try{
    const int MAX = 7;
    Stack<int> s1(MAX);
    cout << s1 << endl;
    for (register int i=0; !s1.isfull(); ++i)
        s1.push(i);
    cout << s1 << endl;
//  s1.push(666);
    while ( !s1.isempty() )
        cout << "Pop val = " << s1.pop() << "; " << s1 << endl;
}
catch(Stack<int>::Bad_index& ex)
{
    cout << ex.what() << endl;
    exit(1);
}