How are base class constructors called in c++ [duplicate]

Answer 1

If the Base constructor you want to call from Derived isn't the default, simply use an initialisation list, something like:

Derived::Derived() : Base(args) {
    // ...
}

Answer 2

first of all constructor of base class is called. it is so because it is inherited in derived class so the order to call the constructors would be like that the class which is inherited first ,its constructor is called first and then the constructor of the class which is inheriting the base class is called. let us take an example

class a: public b,public c,public d
 { ....
  }

then it will call the constructor of class b first then c then d and then a.

In the case of destructor, you have made the destructor of base class as virtual so when you writing delete Var , it is calling destructor of derived class. and at the end to delete all the objects, the destructor of base class is called.

Answer 3

You do not need to call the base constructor in a derived one. This is done automatically - always. If you want to call a constructor explicitly you may do so at any time by specifying the class namespace and constructor (which should be the same) like this:

PointerToObject->ClassName::ClassName(Parameters);

(But this is considederd a "NoNo!" - bad style, because it should not be neccessary in case of good design)