Question

Suppose i have a base class “person”. and i publically inherits a class “student ” from the base class “person”. i have not written the copy constructor for base and the derived class. now suppose i write in the main program

main()
{
student sobj1("name", "computer science");
student sobj2=sobj1;
}

now in the second line the default compiler generated copy constructor of the student will be called but before the execution the default copy constructor of the base class will be called which creates an anonymous object and initialize it then control comes back to the copy constructor of the student which initialize the student’s portion of the object.

this is the demonstration for the situation where we don’t write the copy constructor
now suppose we write the copy constructor for both the classes , then i have tested that when i write

student sobj2=sobj1;

what happens is , this line calles the copy constructor of the student which works , but the copy constructor of the bases class will not be called in this case(default constructor of the base class will be called) my question is why?

Answer 1

I believe the rules are following:

1. Constructor of base class always should be called before constructor of derived class.
2. You can choose which one of base class constructors will be called by calling it explicitly in initialization list.
3. If you do not do that, default constructor is called.
4. When class has no copy constructor, compiler generates one instead. It will call default constructors for all the members of the class and copy constructor of base class, just as your hand written constructor actually should.

So, there you go. Unless you call copy constructor of base class, default one will be used BUT compiler is smart enough to actually call it in it’s own generated copy constructor.

Just in case you do not know how to call it, there example

Student(Student const & p): Person(p) {
}