Chapter 29

Question 1

What are abstract classes

Answer 1

To implement an abstract concept. Abstract classes can not be instantiated. It can inherit.

Question 2

how we define pure virtual function in c+++

Answer 2

virtual void draw() = 0;

Question 3

Does not we need to use body of virtual function most often

Answer 3

Yes

Question 4

Does the class having pure virtual function(s) becomes abstract and then it can not be instantiated.

Answer 4

Yes

Question 5

What happened to derived class which base class has virtual function

Answer 5

Derived class also remain abstract until we make the virtual function non-pure. We do it by over-riding the virtual function(s) in base class and remove 0 from its deceleration.

Question 6

Does order of execution of destructor reverse than constructor

Answer 6

Yes. First called derived class destructor, then its base class and then its base class.

Question 7

Can we make the destructor virtual

Answer 7

Yes

Question 8

What is the use of virtual functions

Answer 8

• To inherit interface and implementation

- Just inherit interface (pure virtual)

Question 9

What is VTable

Answer 9

Compilers build a VTable (virtual function table) array for each class having virtual functions. A vtable array contains a pointer for each its associated virtual function.

Question 10

How compiler deals with virtual functions and non-virtual functions

Answer 10

For non-virtual functions compiler just generate the code to call the function.
For virtual functions, compiler generates code to
- access the object
- access the VTable
- call the associated function.

Question 11

Does polymorphism and virtual function a over head

Answer 11

Yes