Override keyword in C++

The override keyword is extremely important in C++ for assuring your code's correctness and maintainability, especially in object-oriented programming and polymorphism. It is a C++11 (and later) feature that allows you to express explicitly that a derived class member function is meant to override a virtual function specified in a base class. This keyword improves code readability, detects potential problems at compile time, and helps achieve the benefits of variable binding and runtime polymorphism.

The Fundamentals of Polymorphism

Before we go into the override of a keyword, let's go through the basics of polymorphism in C++. Polymorphism is a key concept in object-oriented programming (OOP) because it allows objects of various classes to be viewed as objects of the same base class. It allows you to develop more general code to interact with objects of various derived classes without knowing their precise types during compilation.

Polymorphism in C++ is generally implemented using virtual functions and inheritance. A virtual function is a member function defined with the virtual keyword in a base class. It allows for dynamic binding, in which the right function implementation is decided at runtime according to the type of the real object.

Example:

#include <iostream>
class Animals {
public:
 virtual void makeSounds() {
 std::cout << "Some generic animal sound" << std::endl;
 }
};

class Dog : public Animals {
public:
 void makeSounds() override {
 std::cout << "Cat! Cat" << std::endl;
 }
};

int main() {
 Animals* pt = new Dog();
 pt->makeSounds(); // Calls Dog's makeSounds() dynamically
 delete pt;
 return 0;
}

Output:

Cat! Cat

Explanation:

In this example, we have a base class, Animals, with a virtual function makeSounds(). The derived class Dog overrides this function to give its implementation. In the main method, we construct a Dog object and call the makeSound() function with an Animal* pointer. The necessary implementation in Dog is identified at runtime because of dynamic binding.

Override Keyword

The override keyword was introduced in C++11 to improve the safety and readability of polymorphic code. Its main role is explicitly expresses that a derived class function overrides a virtual function within a base class.

Explicit Intent: By using override, we explicitly tell the compiler and anyone reading the code whether this function is intended to override a virtual function from the base class. It decreases the possibility of accidental function signature mismatches, which can lead to subtle and difficult-to-debug errors.

Compile-Time Checks: When you use override, the compiler examines whether the base class has a virtual function with the same name and signatures. If there isn't, a compilation error is generated, which prevents runtime issues caused by unintended function names or argument changes.

Consider the example:

class Animal {
public:
 virtual void makeSounds() {
 std::cout << "Some generic animal sound" << std::endl;
 }
};

class Dog : public Animal {
public:
 void makesSound() override { // Error: function name mismatch
 std::cout << "Woof! Woof!" << std::endl;
 }
};

There is a typographical problem in the function name in the Dog class. This error would go unreported without override, perhaps leading to unexpected behaviour. With override, however, the compiler detects the problem at compilation time.

Maintenance and refactoring: Maintaining track of overridden methods can be difficult when working on a big codebase with various inheritance levels. The override keyword is record-keeping, making the code easier to comprehend and maintain. If we need to modify the virtual function signature of the base class, the compiler will notify us of all the derived classes that need to be updated.

Common Errors and Best Practices

While the override keyword is a powerful tool, it is essential that it is used correctly and that you are aware of a few possible pitfalls:

Correct Signature: Make that the override function in the class that was derived has the same name, return type, and parameters list as the virtual method in the base class. Even minor differences can cause compilation issues or unpredictable runtime behaviour.

Inheritance Chain: If we have a class hierarchy, ensure each level correctly uses overwrite for methods meant to override virtual methods from the base class. It makes sure the desired behaviour is preserved throughout the inheritance chain.

Final Keyword: In addition to override, C++ includes the final keyword. We can use the final to indicate that virtual functions in the base class shouldn't have to be overridden further within derived classes. It is important for designing limitations or optimizing designs.

Use override Consistently: Use the override keyword consistently across our codebase to maximize its advantages. Even if the compiler doesn't require it in more ancient code, don't omit it. With override, it is beneficial for us and other code contributors to clearly state the reasons for doing so.

Example:

#include<iostream>
class Birds {
public:
 virtual void fly() {
 std::cout << "The Generic fly\n";
 }
};
class Peacock : public Birds {
public:
 void fly() override {
 std::cout << "The bird flies with wings.\n?;
 }
};
int main() {
 Birds * b = new Peacock();
 b->fly();
 return 0;
}

Output:

The bird flies with wings.

Explanation:

The result is "The bird flies with wings" because the code used in the Peacock-derived class overrides a virtual function in the fly base class.

The override identifier within this derived function tells the compiler that this one overrides a function with a comparable name and parameters.

Advantages of using override keyword

There are several advantages of the Override Keyword. Some main advantages of the Override Keyword are as follows:

Checking the compilation time - Using the override keyword, the compiler may detect whether or not a function in a derived class overrides the code implementation of a virtual function in the base class. It assists the programmer in writing bug-free code and identifying bugs at compile time rather than run time.

Maintainability - If the virtual function of the base class changes in future versions, we can use this identifier to modify all the derived classes that override this method, assisting in the maintenance of a large code base.

Readability - If we have appropriate identifiers in our code that show whether a function overrides a virtual function, different developers working on the same code base will discover the code to be more obvious and intelligible.

Disadvantages of using override keyword

There are several disadvantages of the Override Keyword. Some main disadvantages of the Override Keyword are as follows:

Confusion and errors - If the overridden method in the base class is altered, the overridden method in the class that was derived may not work as intended. For example, if the base class method raises an exception, the derived class methods may be unable to handle it.

Reduced Maintainability - When there are a lot of overridden methods, it can be challenging to keep track of which ones are overridden and how they're implemented. As a result, code is difficult for individuals to comprehend and maintain.

Reduced Performance - Overriding methods may result in additional method calls, reducing performance. It is because the overridden method in the derived class must initially call the base class method before executing its code.

Less Flexibility - Overridden methods cannot be reused in other classes. It is due to the simple reason that the overridden method within the derived class is unique to the class that was derived.

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