Explain the concept of a virtual function table in object-oriented programming.

The virtual function table (vtable) is a mechanism used in C++ to implement polymorphism through virtual functions. When a class contains virtual methods, the compiler creates a special table of pointers to these functions. Each object of such a class contains a hidden pointer to this table.

When calling a virtual function through a pointer or reference to the base class, the program accesses the vtable to determine which version of the function to call — the base or the overridden one in the derived class. This allows for dynamic (runtime) polymorphism.

Example:

#include <iostream>

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

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

int main() {
    Base* obj = new Derived();
    obj->show(); // Calls Derived::show thanks to vtable
    delete obj;
    return 0;
}

Here, the call obj->show() during runtime determines that the method from the Derived class should be called, not from Base, thanks to the virtual function table.