Should I use virtual, override, or both keywords?

In C++, the choice of using virtual and override keywords depends on the specific functionality and design goals you aim to achieve. These keywords are typically used in object-oriented programming for classes and inheritance hierarchies. I will explain each keyword individually and the scenarios where they should be used.

1. Using the virtual Keyword

The virtual keyword is used in the function declaration of a base class to allow the function to be overridden in derived classes. This forms the basis for implementing polymorphism.

Example:

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

In this example, the show() function is marked as virtual, indicating that it can be overridden in any derived class that inherits from Base.

2. Using the override Keyword

The override keyword is used in derived classes to explicitly indicate that the function is overriding a virtual function from the base class. This helps the compiler verify that the function signature matches exactly, preventing errors due to accidental overloading rather than overriding.

Example:

cpp
class Derived : public Base {
public:
    void show() override {  // Using `override` ensures correct overriding of the base class virtual function
        cout << "Display Derived Class" << endl;
    }
};

In this example, the show() function in the Derived class is marked with override, indicating it is intended to override the show() function from the Base class.

3. Using Both virtual and override

In certain cases, you may need to use the virtual keyword in derived classes, especially when you want the derived class to be inheritable by other classes and its functions to be further overridden. Using override ensures the correct overriding.

Example:

cpp
class FurtherDerived : public Derived {
public:
    virtual void show() override {  // Using both `virtual` and `override`
        cout << "Display Further Derived Class" << endl;
    }
};

In this example, the show() function in the FurtherDerived class uses both virtual and override, indicating that it overrides the function from the Derived class and can be further overridden by subsequent derived classes.

Summary

• Using virtual: When you define a function that may be overridden in derived classes.
• Using override: When you override a virtual function from the base class in a derived class to ensure signature matching.
• Using Both: When you override the base class function and allow it to be further overridden in derived classes of the current class.

Choosing the appropriate keyword based on your specific requirements and design goals can make your code safer and clearer.