Question

We know the need for a virtual destructor.

Base *bptr = new Derived();
delete bptr;

If a derived class object is pointed by a base class pointer and when the object goes out of scope, only the Base class destructor gets called unless the destructor is virtual.

I am wondering how does the constructor work properly in this case.
Since the Base pointer points to the Derived object, only the Base constructor should have got called. How is it calling the derived class constructor properly.

Please explain me the reason behind this.

Answer 1

While creating the object with new we have the complete information of the object;

new Derived(); // static type is same as dynamic type

LHS part where you assign pointer is irrelevant. That’s why you don’t need such virtual mechanism for constructor. See Bjarne Stroustrup‘s page for more info.

Other note, virtual destructor is needed, because you are using pointer to delete the object.

delete bptr; // static type may not be same as dynamic type