why this is happen ?
When u create abstract class in c++ Ex: Class A (which has a pure virtual function) after that class B is inherited from class A
And if class A has constructor called A() suppose i created an Object of class B then the compiler initializes the base class first i.e.class A and then initialize the class B Then…….?
First thing is we can not access a constructor of any class without an Object then how it is initialize the constructor of abstract class if we can not create an object of abstract class .
Quick answer: constructors are special.
When the constructor of A is still running, then the object being constructed is not yet truly of type A. It’s still being constructed. When the constructor finishes, it’s now an A.
It’s the same for the derived B. The constructor for A runs first. Now it’s an A. Then the constructor for B starts running. During this, the object is still really an A. Only when B’s constructor finishes does it become a B.
You can verify this by trying to call the pure virtual function from the constructors. If the function is defined in A, and B’s constructor calls it, there will be a runtime error instead of running B’s override, because the object is not of type B yet.
The compiler will not allow you to generate code that will construct an A, due to the pure virtual function. But it will generate code to construct an A as part of the process of constructing a B. There’s no magic involved in this. The rule that you cannot construct an A is imposed by the language rules, not by physics. The language lifts that rule under the special circumstance of constructing objects of B.