operator<< and templates

[mickey]

Hello,
how can I overload << with templates, please?

template <class T = int, size_t N = 100>
class Stack {
	T _data[N];
	size_t _index;
 
public:
	Stack() : _index(0) { }
	void push(const T& value) {
		if ( _index != N) _data[_index] = value;
		else printf("stack full\n");
	}
 
 
	friend std::ostream& operator<<(std::ostream& os, const Stack<T>& stack) {
		for (int i=0; i < N; ++i)
			os << _data[i] << "  ";
		return os;
	}
};

template <class T = int, size_t N = 100>
class Stack {
	T _data[N];
	size_t _index;

public:
	Stack() : _index(0) { }
	void push(const T& value) {
		if ( _index != N) _data[_index] = value;
		else printf("stack full\n");
	}

	
	friend std::ostream& operator<<(std::ostream& os, const Stack<T>& stack) {
		for (int i=0; i < N; ++i)
			os << _data[i] << "  ";
		return os;
	}
};

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error C2597: illegal reference to non-static member 'Stack<>::_data'
.....and others.....

error C2597: illegal reference to non-static member 'Stack<>::_data'
.....and others.....

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[DeepDiver]

Hi,
try this:
1.) move the operator<< outside the class
2.) add the template declaration to the operator (template <class T = int, size_t N = 100>)
3.) fix the compiler error: _data is a member of stack

Take care,

Tom

[mcosta]

Your code has two error:

1) You cannot define friend function body in the class declaration

2) You must declare friend function as template

3) In push function you must increment _index

The following code compile and run right

#include <iosfwd>
 
template <class T = int, size_t N = 100>
class Stack {
        T _data[N];
        size_t _index;
 
    public:
        Stack() : _index(0) { }
        void push(const T& value) {
            if ( _index != N) 
            {
            	_data[_index] = value;
            	++_index;
            }
            else 
            	printf("stack full\n");
        }
 
        template <typename TYPE, size_t SIZE>
        friend std::ostream& operator<<(std::ostream& os, const Stack<TYPE, SIZE>& stack);
};
 
template <typename T, size_t N>
std::ostream& operator<<(std::ostream& os, const Stack<T, N>& stack)
{
    for (size_t i=0; i < stack._index; ++i)
        os << stack._data[i] << "  ";
    return os;
}

#include <iosfwd>

template <class T = int, size_t N = 100>
class Stack {
        T _data[N];
        size_t _index;

    public:
        Stack() : _index(0) { }
        void push(const T& value) {
            if ( _index != N) 
            {
            	_data[_index] = value;
            	++_index;
            }
            else 
            	printf("stack full\n");
        }

        template <typename TYPE, size_t SIZE>
        friend std::ostream& operator<<(std::ostream& os, const Stack<TYPE, SIZE>& stack);
};

template <typename T, size_t N>
std::ostream& operator<<(std::ostream& os, const Stack<T, N>& stack)
{
    for (size_t i=0; i < stack._index; ++i)
        os << stack._data[i] << "  ";
    return os;
}

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int main()
{
	Stack<int, 10> st;
	st.push(2);
	st.push(5);
	st.push(3);
 
	std::cout << st << std::endl;
 
	return 0;
}

int main()
{
	Stack<int, 10> st;
	st.push(2);
	st.push(5);
	st.push(3);
		
	std::cout << st << std::endl;
	
	return 0;
}

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[mickey]

sorry,
this code seems work properly; I missed "stack." in os << _data. why does it work?

template <class T = int, size_t N = 3>
class Stack {
	//enum { N = 100 };
	T _data[N];
	size_t _index;
 
public:
	Stack() : _index(0)  { }
	void push(const T& value) {
		if ( _index != N) _data[_index++] = value;
		else printf("stack full\n");
	}
 
	friend std::ostream& operator<< (std::ostream& os, const Stack<T>& stack) {
		for (int i=0; i < N; ++i)
			os << stack._data[i] << "   ";
 
		return os << endl;
	}
 
};

template <class T = int, size_t N = 3>
class Stack {
	//enum { N = 100 };
	T _data[N];
	size_t _index;

public:
	Stack() : _index(0)  { }
	void push(const T& value) {
		if ( _index != N) _data[_index++] = value;
		else printf("stack full\n");
	}
	
	friend std::ostream& operator<< (std::ostream& os, const Stack<T>& stack) {
		for (int i=0; i < N; ++i)
			os << stack._data[i] << "   ";

		return os << endl;
	}

};

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