Base class pointers in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a base class pointer in C++?

A base class pointer is a pointer that points to an object of the base class or any of its derived classes. It allows accessing base class members and supports polymorphism when used with virtual functions.

beginner

How does a base class pointer behave when pointing to a derived class object?

A base class pointer can point to a derived class object, but it can only access members defined in the base class unless virtual functions are used to enable polymorphic behavior.

intermediate

Why do we use virtual functions with base class pointers?

Virtual functions allow a base class pointer to call the derived class's overridden function at runtime, enabling dynamic dispatch and polymorphism.

intermediate

What happens if a base class pointer calls a non-virtual function overridden in a derived class?

The base class version of the function is called, not the derived class version, because non-virtual functions are resolved at compile time based on the pointer type.

beginner

Show a simple example of a base class pointer pointing to a derived class object and calling a virtual function.

#include <iostream>
using namespace std;

class Base {
public:
    virtual void show() { cout << "Base show" << endl; }
};

class Derived : public Base {
public:
    void show() override { cout << "Derived show" << endl; }
};

int main() {
    Base* ptr = new Derived();
    ptr->show(); // Output: Derived show
    delete ptr;
    return 0;
}

What does a base class pointer point to in C++?

A An object of the base class or any derived class

B Only objects of the base class

C Only objects of the derived class

D Only static members of the base class

A base class pointer can point to objects of the base class or any class derived from it.

Which keyword enables a base class pointer to call the derived class's overridden function?

A static

B override

C virtual

D const

The 'virtual' keyword allows dynamic dispatch so the derived class's function is called.

If a base class pointer calls a non-virtual function overridden in a derived class, which function is executed?

A Base class function

B Derived class function

C Both functions

D Compilation error

Non-virtual functions are resolved at compile time based on pointer type, so base class function runs.

What is the output of this code snippet? class Base { public: virtual void f() { cout << "Base"; } }; class Derived : public Base { public: void f() override { cout << "Derived"; } }; Base* p = new Derived(); p->f();

A Base

B No output

C Compilation error

D Derived

Because f() is virtual, the derived class version is called at runtime.

Can a base class pointer access members unique to the derived class?

A Yes, always

B Only if the pointer is cast to derived class type

C No, only base class members are accessible

D Only if the member is virtual

To access derived-only members, the pointer must be cast to the derived class type.

Explain how base class pointers support polymorphism in C++.

Think about how the pointer calls functions depending on the actual object type.

Describe what happens when a base class pointer calls a non-virtual function overridden in a derived class.

Consider how the compiler decides which function to call.