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overloaded << issue

kmce (180)
I have overloaded the operator << but I am getting the error binary '[': no operator found which takes a left-hand operand of type 'const array<T>' (or there is no acceptable conversion), but I dont understand why, this is the way ive overloaded before and it worked all the other times

Overloaded function at bottom of the stack class.
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  #pragma once
#include <iostream>
#include "array.h"

template <typename T>
class stack
{
private:
	int Top = -1;
	int count = 0;
	array<T> Array;

public:
	explicit stack(int size) :  Array(size) { }

	void Push(const T &value)
	{
		Top++;
		Array[Top] = value;	
		count++;
	}

	T Pop()
	{
		count--;
		T element = Array[Top];
		Top--;
		return element;		
	}

	bool isEmpty() const
	{
		return (count == 0);
	}

	int returnSize() const
	{
		return count;
	}

	friend std::ostream& operator << (std::ostream& stream, const stack<T> & obj)
	{
		if (obj.isEmpty())
		{
			stream << "Stack is empty\n";
		}
		else
		{
			for (int i = obj.Top; i>= 0; i--)
			{
				stream << obj.Array[i] << " ";
			}			
		}
		return stream;		
	}


};


array class if needed

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#pragma once
template <typename T>
class array
{
private:
	T* ptr = nullptr;
	int size;

public:
	array(int Size) : size(Size)
	{
		ptr = new T[size];
	}

	~array()
	{
		delete ptr;
		ptr = nullptr;
	}

	int arraySize()
	{
		return size;
	}
	//Access to index
	T& operator[] (int index)
	{
		return index;
	}
	
	friend std::ostream& operator << (std::ostream& stream, const array<T>& obj)
	{
		stream << "[";
		for (int i = 0; i < obj.arraySize(); i++)
		{
			stream << obj[i] << ",";
		}
		stream << " ]";
		return stream;
	}
	
};
dutch (2548)
The problem is with your operator[] definition in array. Try:

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	T& operator[] (int index)
	{
		return ptr[index];
	}

	const T& operator[] (int index) const
	{
		return ptr[index];
	}

You're also missing const on arraySize().

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	int arraySize() const
	{
		return size;
	}

You shouldn't need both count and Top. They're virtually the same.
And the delete for array should be delete[].
Also, your push and pop should check for overflow or underflow.
Last edited on
seeplus (6597)
Consider:

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#include <iostream>

template <typename T>
class array
{
private:
	T* ptr {};
	size_t size {};

public:
	array() {}
	array(size_t Size) : size(Size), ptr(new T[Size]) {}
	~array() { delete [] ptr; }

	size_t arraySize() const { return size; }
	T& operator[] (size_t index) { return ptr[index]; }
	const T& operator[] (size_t index) const { return ptr[index]; }

	friend std::ostream& operator << (std::ostream& stream, const array<T>& obj)
	{
		stream << "[ ";

		for (size_t i = 0; i < obj.arraySize(); ++i) {
			if (i != 0) stream << ", ";
			stream << obj[i];
		}

		return stream << " ]";
	}
};

template <typename T>
class stack
{
private:
	size_t count {};
	array<T> Array;

public:
	stack() {}
	explicit stack(size_t size) : Array(size) { }

	void Push(const T& value) { Array[count++] = value; }

	T Pop() { return Array[--count]; }

	bool isEmpty() const { return count == 0; }

	int returnSize() const { return count; }

	friend std::ostream& operator << (std::ostream& stream, const stack<T>& obj)
	{
		if (obj.isEmpty())
			return stream << "Stack is empty\n";

		for (size_t i = obj.count; i > 0; --i)
			stream << obj.Array[i - 1] << " ";

		return stream;
	}
};

int main()
{
	stack<int> s(5);

	s.Push(1);
	s.Push(2);
	std::cout << s << "\n\n";

	s.Pop();
	std::cout << s << '\n';
}



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dutch (2548)
@seeplus, consider:

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// array.h //////////////////////////////////////////

// pragma once
#include <ostream>
#include <algorithm>
#include <utility>

template <typename T>
class Array
{
private:
    size_t m_size;
    T*     m_data;
public:
    Array(size_t size) : m_size(size), m_data(new T[size]) { }

    Array(const Array& other)
    {
        m_size = other.m_size;
        m_data = new T(other.m_size);
        std::copy(other.m_data, other.m_data + other.m_size, m_data);
    }

    Array(Array&& other)
    {
        m_size = other.m_size;
        m_data = other.m_data;
        other.m_size = 0;
        other.m_data = nullptr;
    }

    Array& operator=(const Array& other)
    {
        if (this = &other) return *this;
        if (size != other.size)
        {
            delete[] m_data;
            m_data = nullptr;
            m_size = 0; // preserve invariants (in case next line throws(
            m_data = new T[other.m_size];
            m_size = other.m_size;
        }
        std::copy(other.m_data, other.m_data + other.size, m_data);
        return *this;
    }

    Array& operator=(Array&& other)
    {
        if (this = &other) return *this;
        delete[] m_data;
        m_data = std::exchange(other.m_data, nullptr);
        m_size = std::exchange(other.size, 0);
        return *this;
    }

    ~Array() { delete[] m_data; }

    size_t size() const { return m_size; }

    T& operator[](size_t index) { return m_data[index]; }

    const T& operator[](size_t index) const { return m_data[index]; }
    
    friend std::ostream& operator<<(std::ostream& out, const Array<T>& obj)
    {
        out << '[';
        for (size_t i = 0; i < obj.m_size; ++i)
            out << (i ? "," : "") << obj.m_data[i];
        return out << ']';
    }
};


// stack.h //////////////////////////////////////////

// pragma once
#include <ostream>
#include <stdexcept>
#include <utility>
//#include "array.h"

template <typename T>
class Stack
{
private:
    size_t   m_top   = 0;
    Array<T> m_array;

public:
    struct StackError : public std::runtime_error
    {
        StackError(const std::string& what) : runtime_error(what) { }
    };

    explicit Stack(size_t size) : m_array(size) { }

    Stack(const Stack& s) { m_top = s.m_top; m_array = s.m_array; }

    Stack(Stack&& s)
    {
        m_top = s.m_top;
        s.m_top = 0;
        m_array = std::move(s.m_array);
    }

    Stack& operator=(Stack other)
    {
        std::swap(m_top, other.m_top);
        std::swap(m_array, other.m_array);
        return *this;
    }

    void push(const T& value)
    {
        if (m_top == m_array.size()) throw StackError("overflow");
        m_array[m_top++] = value;
    }

    T pop()
    {
        if (empty()) throw StackError("underflow");
        return m_array[--m_top];        
    }

    bool empty() const { return m_top == 0; }

    size_t size() const { return m_top; }

    friend std::ostream& operator<<(std::ostream& out, const Stack<T>& obj)
    {
        if (obj.empty())
            out << "<empty>";
        else
            for (size_t i = obj.m_top; i-- > 0; )
                out << obj.m_array[i] << ' ';
        return out;
    }
};


// main.cpp ////////////////////////////////////////////

#include <iostream>

int main()
{
    using std::cout;

    Stack<int> s(10);

    cout << "Pushing:\n";
    for (int i = 0; i < 9; ++i)
    {
        cout << i << ' ' << std::flush;
        s.push(i);
    }

    cout << "\nPopping:\n";
    for (int i = 0; i < 6; ++i) cout << s.pop() << ' ' << std::flush;

    cout << "\nPrinting:\n";
    cout << s << '\n';
}

seeplus (6597)
@dutch. OK. I just cleaned up the OP code and didn't provide the extra member functions required for them to be fully functioning classes. I probably should have. My bad.

PS Shouldn't L20 be

 
 
m_data = new T[other.m_size];


L34
 
 
if (this == &other) return *this;


L49
 
 
if (this == &other) return *this;


giving:

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#include <iostream>
#include <algorithm>
#include <utility>
#include <stdexcept>

template <typename T>
class Array
{
private:
	size_t m_size {};
	T* m_data {};
public:
	Array() {}
	Array(size_t size) : m_size(size), m_data(new T[size]) { }

	Array(const Array& other) : m_size(other.m_size), m_data(new T[other.m_size])
	{
		std::copy_n(other.m_data, m_size, m_data);
	}

        Array(Array&& other) : m_size(other.m_size), m_data(std::exchange(other.m_data, nullptr)) {}

	Array& operator=(const Array& other)
	{
		if (this != &other) {
			if (size != other.size) {
				delete[] m_data;
				m_data = nullptr;
				m_size = 0; // preserve invariants (in case next line throws(
				m_data = new T[other.m_size];
				m_size = other.m_size;
			}

			std::copy_n(other.m_data, other.size, m_data);
		}
		return *this;
	}

	Array& operator=(Array&& other)
	{
		if (this != &other) {
			delete[] m_data;
			m_data = std::exchange(other.m_data, nullptr);
			m_size = std::exchange(other.size, 0);
		}
		return *this;
	}

	~Array() { delete[] m_data; }

	size_t size() const { return m_size; }

	T& operator[](size_t index) { return m_data[index]; }

	const T& operator[](size_t index) const { return m_data[index]; }

	friend std::ostream& operator<<(std::ostream& out, const Array<T>& obj)
	{
		out << '[';
		for (size_t i = 0; i < obj.m_size; ++i)
			out << (i ? "," : "") << obj.m_data[i];

		return out << ']';
	}
};

template <typename T>
class Stack
{
private:
	size_t   m_top {};
	Array<T> m_array {};

public:
	struct StackError : public std::runtime_error
	{
		StackError(const std::string& what) : runtime_error(what) { }
	};

	Stack() {}
	explicit Stack(size_t size) : m_array(size) { }

	Stack(const Stack& s) : m_top(s.m_top), m_array(s.m_array) {}

	Stack(Stack&& s) : m_top(s.m_top), m_array(std::move(s.m_array)) {}

	Stack& operator=(Stack other)
	{
		std::swap(m_top, other.m_top);
		std::swap(m_array, other.m_array);
		return *this;
	}

	void push(const T& value)
	{
		if (m_top == m_array.size())
			throw StackError("overflow");

		m_array[m_top++] = value;
	}

	T pop()
	{
		if (empty())
			throw StackError("underflow");

		return m_array[--m_top];
	}

	bool empty() const { return m_top == 0; }

	size_t size() const { return m_top; }

	friend std::ostream& operator<<(std::ostream& out, const Stack<T>& obj)
	{
		if (obj.empty())
			return out << "<empty>";

		for (size_t i = obj.m_top; i-- > 0; )
			out << obj.m_array[i] << ' ';

		return out;
	}
};

int main()
{
	using std::cout;

	Stack<int> s(10);

	cout << "Pushing:\n";
	for (int i = 0; i < 9; ++i)
	{
		cout << i << ' ';
		s.push(i);
	}

	cout << "\nPopping:\n";
	for (int i = 0; i < 6; ++i)
		cout << s.pop() << ' ';


	cout << "\nCopying to s1";
	auto s1 {s};

	cout << "\nPrinting:\n";
	cout << s1 << '\n';
}



Pushing:
0 1 2 3 4 5 6 7 8
Popping:
8 7 6 5 4 3
Copying to s1
Printing:
2 1 0

Last edited on
seeplus (6597)
and using swap and noexcept:

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#include <iostream>
#include <algorithm>
#include <utility>
#include <stdexcept>

template <typename T>
class Array
{
private:
	size_t m_size {};
	T* m_data {};
public:
	Array() noexcept {}
	Array(size_t size) : m_size(size), m_data(new T[size]) {}

	Array(const Array& other) : m_size(other.m_size), m_data(new T[other.m_size])
	{
		std::copy_n(other.m_data, m_size, m_data);
	}

	Array(Array&& other) noexcept : m_size(other.m_size), m_data(std::exchange(other.m_data, nullptr)) {}

	void swap(Array& other) noexcept
	{
		std::swap(m_size, other.m_size);
		std::swap(m_data, other.m_data);
	}

	Array& operator=(const Array& other)
	{
		if (m_size >= other.m_size) {
			m_size = other.m_size;
			std::copy_n(other.m_data, m_size, m_data);
		} else {
			Array tmp(other);

			swap(tmp);
		}
		return *this;
	}

	Array& operator=(Array&& other) noexcept
	{
		swap(other);
		return *this;
	}

	~Array() { delete[] m_data; }

	size_t size() const noexcept { return m_size; }

	T& operator[](size_t index) { return m_data[index]; }

	const T& operator[](size_t index) const { return m_data[index]; }

	friend std::ostream& operator<<(std::ostream& out, const Array<T>& obj)
	{
		out << '[';
		for (size_t i = 0; i < obj.m_size; ++i)
			out << (i ? "," : "") << obj.m_data[i];

		return out << ']';
	}
};

template <typename T>
class Stack
{
private:
	size_t   m_top {};
	Array<T> m_array {};

public:
	struct StackError : public std::runtime_error
	{
		StackError(const std::string& what) : runtime_error(what) {}
	};

	Stack() noexcept {}
	explicit Stack(size_t size) : m_array(size) { }

	Stack(const Stack& s) : m_top(s.m_top), m_array(s.m_array) {}

	Stack(Stack&& s) noexcept : m_top(s.m_top), m_array(std::move(s.m_array)) {}

	void swap(Stack& other) noexcept
	{
		std::swap(m_top, other.m_top);
		std::swap(m_array, other.m_array);
	}

	Stack& operator=(const Stack& other)
	{
		if (m_top >= other.m_top) {
			m_array = other.m_array;
			m_top = other.m_top;
		} else {
			Stack tmp(other);

			swap(tmp);
		}
		return *this;
	}

	Stack& operator=(Stack&& other) noexcept
	{
		swap(other);
		return *this;
	}

	void push(const T& value)
	{
		if (m_top == m_array.size())
			throw StackError("overflow");

		m_array[m_top++] = value;
	}

	T pop()
	{
		if (empty())
			throw StackError("underflow");

		return m_array[--m_top];
	}

	bool empty() const noexcept { return m_top == 0; }

	size_t size() const noexcept { return m_top; }

	friend std::ostream& operator<<(std::ostream& out, const Stack<T>& obj)
	{
		if (obj.empty())
			return out << "<empty>";

		for (size_t i = obj.m_top; i-- > 0; )
			out << obj.m_array[i] << ' ';

		return out;
	}
};

int main()
{
	using std::cout;

	Stack<int> s(10);

	cout << "Pushing:\n";
	for (int i = 0; i < 9; ++i)
	{
		cout << i << ' ';
		s.push(i);
	}

	auto s2 {s};

	cout << "\nPopping:\n";
	for (int i = 0; i < 6; ++i)
		cout << s.pop() << ' ';

	cout << "\nCopying to s1";
	auto s1 {s};

	cout << "\nPrinting:\n";
	cout << s1 << '\n';

	s1 = s2;
	cout << s1 << '\n';
}

Last edited on
seeplus (6597)
and to demonstrate exceptions:

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int main()
{
	using std::cout;

	Stack<int> s(5);

	cout << "Pushing:\n";
	try {
		for (int i = 0; i < 9; ++i)
		{
			cout << i << ' ';
			s.push(i);
		}
	}
	catch (const Stack<int>::StackError& se)
	{
		cout << "\nStack error - " << se.what() << '\n';
	}

	auto s2 {s};

	cout << "\nPopping:\n";

	try {
		for (int i = 0; i < 6; ++i)
			cout << s.pop() << ' ';
	}
	catch (const Stack<int>::StackError& se)
	{
		cout << "\nStack error - " << se.what() << '\n';
	}

	cout << "\nCopying to s1";
	auto s1 {s};

	cout << "\nPrinting:\n";
	cout << s1 << '\n';

	s1 = s2;
	cout << s1 << '\n';
}



Pushing:
0 1 2 3 4 5
Stack error - overflow

Popping:
4 3 2 1 0
Stack error - underflow

Copying to s1
Printing:
<empty>
4 3 2 1 0

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