Initializing objects of an inherited class

Hi! I need to initialize objects of the class from which my class is inherited. For example: class A : public B. The obvious solution would be to call the constructor of class B in the constructor of class A. But when creating an object of class A, you need to use CreateDefaultSubobject or NewObject. They cannot be passed constructor arguments, but I need to pass an instance of class B to initialize its fields in class A. I wouldn’t want to do it manually. Because when adding new fields to class B, I will have to add changes to class A as well. How?