Virtual base classes in C++ prevent multiple instances of a given class in an inheritance hierarchy, particularly during multiple inheritance. By declaring a common base class as a virtual base class, duplication of inherited members is avoided, ensuring only one copy exists for any derived class. The document includes an illustrative C++ code example demonstrating the use of virtual base classes.

1. Virtual Base class
• Virtual base classes are used in virtual inheritance in a way of preventing
multiple “instances” of a given class appearing in an inheritance
hierarchy when using multiple inheritances.
• The duplication of inherited members due to these multiple can be
avoided by making the common base class as virtual base class while
declaring the direct or intermediate base classes.
• When a class is made a virtual base class, C++ takes necessary care to see
that only one copy of that class is inherited, regardless of how many
inheritance path exist between the virtual base class and a derived class.
• The keywords virtual and public may be used in either order.

2. Virtual base class

3. Virtual Base class

4. • #include <iostream>
• using namespace std;
• class A {
• public:
• A() {
• cout << "Constructor An";
• }
• void display() {
• cout << "Hello form Class A n";
• }
• };
• class B: public virtual A
{
• };
• class C: public virtual A
{
• };
• class D: public B, public
C {
• };
• int main() {
• D object;
• object.display();
• }