Virtual functions are a fundamental concept in the world of programming. They allow for polymorphism, a powerful feature that enables objects to take on different forms and behave differently based on their underlying type. However, one aspect of virtual functions that often confuses programmers is their inherent hidden nature. In this article, we will explore the reasons behind this hiddenness and its significance in the world of programming.
To understand why virtual functions are hidden, we must first understand how they work. When a class contains a virtual function, it creates a virtual table, also known as a vtable. This table contains pointers to the virtual functions of the class. When an object of the class is created, it contains a pointer to this vtable. This allows for dynamic binding, which means that the function to be called is determined at runtime based on the actual type of the object, rather than its declared type.
Now, let's consider a scenario where a derived class overrides a virtual function from its base class. In this case, the vtable of the derived class will contain a pointer to the overridden function. However, the vtable of the base class will still contain a pointer to the original function. This is where the hidden nature of virtual functions comes into play. When a virtual function is called on an object of the base class, the function pointer from the vtable of the base class is used. But when the same function is called on an object of the derived class, the function pointer from the vtable of the derived class is used. This is what makes virtual functions hidden – the derived class has effectively hidden the function of the base class.
Now, you might be wondering, why is this hiddenness necessary? The answer lies in the principle of encapsulation. Encapsulation is the practice of bundling data and functions together into a single unit, known as a class. It helps in keeping the implementation details of a class hidden and only exposing the essential information to the outside world. In the case of virtual functions, this hiddenness ensures that the derived class can override the function of the base class without affecting the functionality of the base class itself. This allows for the derived class to have its own unique behavior while still maintaining the functionality of the base class.
Another reason for the hidden nature of virtual functions is efficiency. When a virtual function is called, the program has to go through the vtable to find the correct function pointer. This can lead to a slight performance hit, especially in large programs with multiple virtual functions. By keeping the vtable hidden, the program can access the correct function pointer without having to go through the vtable every time, thus improving performance.
In conclusion, virtual functions are hidden to ensure encapsulation and efficiency. They play a crucial role in achieving polymorphism and enabling objects to take on different forms. By understanding their hidden nature, programmers can make use of virtual functions effectively and create robust, efficient code.
