Quiz on Runtime Polymorphism in C++

What is runtime polymorphism also known as?

• Late binding

• Compile-time polymorphism

• Dynamic polymorphism

• Static polymorphism

Answer explanation

Runtime polymorphism is also known as dynamic polymorphism because it resolves method calls at runtime, allowing for more flexible and reusable code. This contrasts with compile-time or static polymorphism.

Which mechanism is used to implement runtime polymorphism in C++?

• Function hiding

• Operator overloading

• Method overriding

• Function overloading

Answer explanation

Method overriding is the mechanism used to achieve runtime polymorphism in C++. It allows a derived class to provide a specific implementation of a function that is already defined in its base class.

What must be the same for function overriding to occur?

• Return type only

• Function name only

• Argument list only

• Signature or prototype

Answer explanation

For function overriding to occur, the signature or prototype must be the same. This includes the function name and the argument list, ensuring that the derived class method matches the base class method.

In which class is the function overridden?

• Base class

• Friend class

• Abstract class

• Derived class

Answer explanation

The function is overridden in the derived class, which inherits from the base class. This allows the derived class to provide a specific implementation of a function that is already defined in the base class.

What keyword is used to declare a virtual function?

• static

• dynamic

• virtual

• override

Answer explanation

The keyword 'virtual' is used in C++ to declare a virtual function, allowing derived classes to override it. This enables polymorphism, which is a core feature of object-oriented programming.

What does the virtual table (VTABLE) contain?

• Class definitions

• Object instances

• Data members

• Function pointers

Answer explanation

The virtual table (VTABLE) contains function pointers that link to the appropriate methods for a class. This allows for dynamic method resolution in object-oriented programming, enabling polymorphism.

What is the purpose of the _vptr in C++?

• To handle exceptions

• To manage memory

• To point to the VTABLE

• To store object data

Answer explanation

The _vptr is a pointer used in C++ to reference the VTABLE, which contains addresses of virtual functions for a class. This mechanism enables dynamic dispatch, allowing the correct function to be called for an object at runtime.

What happens when a base class pointer points to a derived class object?

• Dynamic binding occurs

• Static binding occurs

• Compile-time error

• No binding occurs

Answer explanation

When a base class pointer points to a derived class object, static binding occurs. This means that the method calls are resolved at compile time, rather than at runtime, which is characteristic of static binding.

What is a pure virtual function?

• A function that cannot be overridden

• A function with default behavior

• A function that can be instantiated

• A function with no implementation

Answer explanation

A pure virtual function is a function declared in a base class that has no implementation. It must be overridden in derived classes, making it essential for defining an interface. Thus, the correct choice is 'A function with no implementation'.

What is an abstract class?

• A class with only static members

• A class that cannot be inherited

• A class with at least one pure virtual function

• A class with no members

Answer explanation

An abstract class is defined as one that contains at least one pure virtual function, making it impossible to instantiate directly. This allows derived classes to implement the abstract methods, ensuring a common interface.