Deck 15: Polymorphism and Virtual Functions

Question 1

A pointer to objects of a derived class can be assigned pointers to objects of the base class in the inheritance hierarchy.

Answer 1

False

Question 2

This is legal code.
class B
{
public:
// ...
virtual void f()= 0;
};
int main(){ B b1,b2;/*...*/ }

Answer 2

False

Question 3

Downcasting causes the slicing problem.

Answer 3

False

Question 4

A derived class destructor always invokes the base class destructor.

Question 5

It is legal to have all member functions of a class be pure virtual functions.

Question 6

Upcasting causes no problems

Question 7

Virtual functions allow old code to call new code.

Question 8

The virtual function mechanism binds the "right" function to objects.

Question 9

It is useful to define a class for which no objects may be defined.

Question 10

Virtual functions are implemented with a table look up that is done at run time.

Question 11

The virtual property is not inherited.

Question 12

No objects can be defined of abstract base class type since it is an incomplete definition.

Question 13

A class that has a pure virtual member function is called a concrete base class.

Question 14

Late binding refers to a failure to secure one's ski boots.

Question 15

A the binding of virtual function is done at runtime if called using an object.

Question 16

In a class,functions declared with the virtual keyword need not be defined.

Question 17

Only member functions can be virtual.

Question 18

It is OK to assign between objects of base type and objects of derived type.

Question 19

Destructors are automatically virtual.

Question 20

The base class destructor must be virtual.

Question 21

Write a program where the destructors should be virtual.Explain.

Question 22

Write a short program that shows how to defeat the slicing problem.

Question 23

Write a class having a public pure virtual method.You need not put any other members in the class.

Question 24

What is the error?
class B
{
public:
virtual void f();
};
virtual void B::f(){/*...*/}

Question 25

Why do you not get an undefined reference in virtual table error when you don't define a pure virtual function?

Question 26

In C++,a virtual destructor is invoked whenever a virtual constructor was used to create the object.

Question 27

If the override specifier is added to the end of a member function declaration,what happens if the function is not specified as virtual in the parent class?

A)The function is overridden in the derived class.
B)There is a compiler error.
C)The function in the parent class will always be invoked.

Question 28

Suppose each of the base class and the derived class has a member function with the same signature.Suppose you have a base class pointer to a derived class object and call the common function member through the pointer.Discuss what determines which function is actually called,whether the one from the base class or the one from the derived class.Consider both the situations where the base class function is declared virtual and where it is not.

Question 29

Redefining and overriding are exactly the same thing.

Question 30

Is there an error?
class B
{
public:
void virtual f();
};
void B::f(){/*...*/}

Question 31

It is desirable to develop your programs incrementally.Code a little,test a little.If you do this with virtual functions,you get into trouble.Discuss the problem and the (very simple)solution.

Question 32

Give some simple recommendation for when a destructor should be declared virtual.

Question 33

Explain the difference between virtual functions,late binding,and polymorphism.

Question 34

Which functions in class D are virtual?
class B
{
public:
virtual void f();
virtual void g();
// ...
private:
//...
};
class D : public B
{
public:
void f();
void g(int);
private:
// ...
};