Re: Alternative to Abtract Class?

I want to know. Is first version of abtract class the same as second
version of class with protected constructor() and destructor()?

is an example. You can't use class A so class B is used to derive
from class A. Also, you can't use class A2 with protected constructor
() so class B2 is used to derive from class A2.

#include <iostream>
using std::cout;
using std::endl;

class A
{
public:
    A() : m_x(0) { cout << "Constructor A" << endl; }
    ~A() { cout << "Destructor A" << endl; }

    void set(int x) { m_x = x; }
    int get() { return m_x; }

    virtual void print() = 0;

private:
    int m_x;
};

class B : public A
{
public:
    B() : A() { cout << "Constructor B" << endl; }
    ~B() { cout << "Constructor B" << endl; }

    void print() { cout << "m_x: " << get() << endl; }
};

class A2
{
protected:
    A2() : m_x(0) { cout << "Constructor A2" << endl; }
    ~A2() { cout << "Destructor A2" << endl; }

    int m_x;
};

class B2 : public A2
{
public:
    B2() : A2() { cout << "Constructor B2" << endl; }
    ~B2() { cout << "Destructor B2" << endl; }

    void set(int x) { A2::m_x = x; }
    int get() { return m_x; }

    void print() { cout << "m_x: " << get() << endl; }
};

int main5()
{
// Compilation Error because of abtract class
// A a;
// a.set( 5 );
// a.print();

    B b;
    b.set( 5 );
    b.print();

// Compilation Error because of protected constructor
// A2 a2;

    B2 b2;
    b2.set( 10 );
    b2.print();

    return 0;
}

Thanks....