Question

I have:

class BASE{
public:
    virtual void func1() = 0;
};

Then I have some derived classes, like:

class Derived1 : public BASE{
public:
    void func1() {...implementation....}
};

class Derived2 : public BASE{
    public:
        void func1() {...implementation....}
    };

In the main I would like to do something like (pseudo code):

if ( cond ){
   BASE b := new Derived1
}
else{
   BASE b := new Derived2
}
b.func1();

so that the func1() function invoked is the one specialized for the derived class.

I tried to do:

BASE b = new Derived1();

but the compiler complains.

Is it possible to do that in C++? How?

Answer 1

There are two ways to do this:

• Use a pointer of type base class:

  Base *b = new Derived1;

• Use a const reference of type base class if you want to create a derived on copy construction:

  Base const& b = Derived;

• Use a non-const reference of type base class if you want to assign a derived class object created elsewhere:

  Derived d;
Base& b = d;

Nits:

• In order to inherit, you need to specify this in the class definition:

  class Derived1 : public Base {

• Your functions need to have a return value.

  class B{
public:
virtual void func() = 0;
};