CPP Object-Oriented Programming & Class Design 2 — Questions and Answers
Question 1: Which access specifier should be used for data members that must be accessible only within the class and its derived classes?
- public
- private
- protected (Correct answer)
- internal
Correct answer: protected
Protected members are accessible within the class itself and by derived classes, but not from outside the class hierarchy.
Question 2: What is the purpose of a copy constructor in C++?
- To create a default-initialized object
- To initialize an object as a copy of another object of the same type (Correct answer)
- To assign one object to another after both are constructed
- To destroy a copy of an object
Correct answer: To initialize an object as a copy of another object of the same type
A copy constructor initializes a new object by copying the state from an existing object of the same type.
Question 3: In C++, what does the 'explicit' keyword prevent when applied to a constructor?
- The constructor from being called with no arguments
- Implicit type conversions using that constructor (Correct answer)
- The constructor from being inherited
- The constructor from throwing exceptions
Correct answer: Implicit type conversions using that constructor
The explicit keyword prevents the compiler from using a constructor for implicit conversions or copy-initialization.
Question 4: What is object slicing in C++?
- Splitting a large class into smaller classes
- Losing derived-class data when a derived object is assigned to a base-class object by value (Correct answer)
- Dividing an array of objects into segments
- Cutting unused methods from a compiled class
Correct answer: Losing derived-class data when a derived object is assigned to a base-class object by value
Object slicing occurs when a derived class object is copied into a base class object by value, stripping away the derived portion.
Question 5: Which of the following correctly declares a pure virtual function in C++?
- virtual void draw() {}
- void draw() = 0;
- virtual void draw() = 0; (Correct answer)
- abstract void draw();
Correct answer: virtual void draw() = 0;
A pure virtual function is declared with 'virtual' and assigned '= 0', making the class abstract.
Question 6: What does the 'this' pointer represent inside a non-static member function?
- A pointer to the class definition
- A pointer to the calling object (Correct answer)
- A pointer to the base class subobject
- A pointer to the vtable
Correct answer: A pointer to the calling object
Inside a non-static member function, 'this' is an implicit pointer to the object on which the function was called.
Question 7: When a class declares a destructor as virtual, what is the primary benefit?
- The destructor can be called multiple times safely
- The correct derived-class destructor is called when deleting through a base-class pointer (Correct answer)
- The destructor runs before any member destructors
- The class becomes abstract
Correct answer: The correct derived-class destructor is called when deleting through a base-class pointer
A virtual destructor ensures that when a derived object is deleted through a base-class pointer, the derived destructor runs first, preventing resource leaks.
CPP Object-Oriented Programming & Class Design 2
Which access specifier should be used for data members that must be accessible only within the class and its derived classes?