CareerCup

The parameters could be of type struct.

Not yet sure what works best, but here are some thoughts I can throw around:

1) If D has no other data members, consider collpasing into one class, get rid of other, either B or D.
2) If that's not desired, create a separate function(s) to process args. Make it the friend function of both B and D, thereby comitting first degree murder of OOP concepts. But, you've accomplished what you wanted (ONE place to update). Bad part is, friend function will need all the logic to differentiate betn B and D inside.... or would it?!
3) Your thoughts here.

we can use the variable number arguments list. Something like printf function uses. As we know printf can take n number of arguments. We can use that facility here. Uee macro va_list, va_start etc...

you could use the ellipsis ("...") as the last argument, representing any variable number of unspecified arguments for the function.

http://www.learncpp.com/cpp-tutorial/714-ellipses-and-why-to-avoid-them/

I think we can use templatized class and make T as a member of B.

Use using B::B; in D's definition to inherit constructors.

I think Default arguments to the base class constuctor will solve this problem

you could use the Builder design pattern. You could create a inner class named Builder or Buildable with setter methods for all the mandatory variables of the outer class and a build method. The caller calls each of the set methods on the Builder class and at the end calls the build method, which sets all the outer class variables and returns an instance of the outer class. You could also NOT provide any setter methods in the outer class, so that the outer class can be constructed only through the inner class build method