abstract class - enforce cannot instantiate

[Christopher]

If I have an generic interface, but _also_ have the implementation for
it and want to use that common implementation in my derived classes,
what method does that leave me to make pure virtual such that my
generic interface class cannot be instantiated?

Do you make the destructor virtual?
Do you move constructors to private?

// What do I make pure virtual??
AbstractClass
{
public:

AbstractClass() {}

virtual AbstractClass() {}

virtual void Foo()
{
std::cout << "Foo!" << std::endl;
}
};


DerivedClass : public AbstractClass
{
public:

DerivedClass() {}

~DerivedClass() {}

void Bar()
{
std::cout << "Bar!" <<std::endl;
}
};


I don't want anyone to be able to:
AbstractClass * abstract = new AbstractClass();

I do want people to be able to:
AbstractClass * abstract = new DerivedClass();
abstract->Foo();

and expect:
"Foo!"

 

[David Côme]

If I have an generic interface, but _also_ have the implementation for
it and want to use that common implementation in my derived classes,
what method does that leave me to make pure virtual such that my
generic interface class cannot be instantiated?

Do you make the destructor virtual?
Do you move constructors to private?

// What do I make pure virtual??
AbstractClass
{
public:

AbstractClass() {}

virtual AbstractClass() {}

virtual void Foo()
{
std::cout << "Foo!" << std::endl;
}
};


DerivedClass : public AbstractClass
{
public:

DerivedClass() {}

~DerivedClass() {}

void Bar()
{
std::cout << "Bar!" <<std::endl;
}
};


I don't want anyone to be able to:
AbstractClass * abstract = new AbstractClass();

I do want people to be able to:
AbstractClass * abstract = new DerivedClass();
abstract->Foo();

and expect:
"Foo!"

class AbstractClass
{
public:

AbstractClass() {}

virtual ~AbstractClass()=0;
virtual void Foo()
{
std::cout << "Foo!" << std::endl;
}
};

AbstractClass::~AbstractClass()
{
std::cout<<"Dest ABC"<<std::endl;
}

With this code, AbstractClass's destructor is virtual pure and well
defined.
Try to instanciate an obbject of type AbstractClass, and you will get an
error.