Using Default Arguments with Virtual Functions

Introduction

C++ is a versatile language that supports several features, including virtual functions and default arguments. Together, these two capabilities can increase the flexibility and maintainability of your code.In this article, we will discuss how to use default arguments with virtual functions in C++.

• Default Arguments

In C++, you can define default arguments for function parameters.You can define a default argument by simply giving the parameter in the function declaration a value. To define a default argument, you simply assign a value to the parameter in the function declaration. For example:

void foo(int x = 0) {
    // function body


}

In the above example, the default value of the parameter x is 0. The function will utilise the value it receives as input in place of the default value. In the absence of a value, the default value of 0 will be applied.

Virtual Functions

A virtual function is a class member function that a derived class may override. When objects of various classes are polymorphic, they can be utilised interchangeably if they share a virtual function. To declare a virtual function in C++, you use the virtual keyword in the function declaration. For example:

class Shape {
public:
    virtual double area() { return 0; }
};

In the above example, the area() function is declared as a virtual function. This means that it can be overridden by a derived class. The implementation in the base class returns 0 as a default value.

Using Default Arguments with Virtual Functions

When you use default arguments with virtual functions, the default argument is used by the derived class if the derived class does not provide its own implementation of the function. Consider the following example:

#include <iostream>
using namespace std;


class Shape {
public:
    virtual double area(double r = 0) { return 0; }
};


class Circle : public Shape {
public:
    double area(double r = 0) override {
        return 3.141592 * r * r;
    }
};


int main() {
    Circle circle;
    Shape* shape = &circle;


    cout << "Area of circle: " << shape->area() << endl; // prints "Area of circle: 0"
    cout << "Area of circle with radius 2: " << shape->area(2) << endl; // prints "Area of circle with radius 2: 12.5664"


    return 0;
}

Explanation

• This program demonstrates the use of default arguments and virtual functions in C++.
• The program defines a base class Shape which has a virtual function named area(). This function takes a parameter r which has a default value of 0. The implementation of this function in the Shape class simply returns 0.
• The Circle class is a derived class of Shape and overrides the area() function. In this implementation, the area() function takes a default parameter r of 0 and calculates the area of the circle using the formula pr^2.
• In the main() function, an object of the Circle class is created, and a pointer of type Shape is assigned to it. The area() function is called on this pointer using shape->area(), which prints 0 since the function is called with the default argument value of 0.
• Next, the area() function is used to compute the area of the circle with a radius of 2 and print the result. This method is called with a value of 2 for the r parameter.

Program Output:

Here is another example program that demonstrates the use of default arguments and virtual functions in C++:

Program

#include<iostream>
using namespace std;


// define a function with default arguments
void myFunction(int x, int y = 0, int z = 1) {
std::cout << "x = " << x << ", y = " << y << ", z = " << z << std::endl;
}


// define a base class with a virtual function
class Shape {
public:
    virtual void draw() {
std::cout << "You can Draw a shape." <<std::endl;
    }
};


// define a derived class that overrides the virtual function
class Circle : public Shape {
public:
    void draw() override {
std::cout <<"You can Draw a circle." << std::endl;
    }
};


int main() {
    // call myFunction with default arguments
myFunction(5);          // output: x = 5, y = 0, z = 1
myFunction(5, 10);      // output: x = 5, y = 10, z = 1
myFunction(5, 10, 15);  // output: x = 5, y = 10, z = 15


    // create instances of Shape and Circle
    Shape* shape = new Shape();
    Circle* circle = new Circle();


    // call the draw() function on the instances
    shape->draw();   // output: Drawing a shape.
    circle->draw();  // output: Drawing a circle.


    // delete the instances
    delete shape;
    delete circle;


    return 0;
}

Explanation:

• The program starts by defining a function myFunction() that takes three integer parameters, with default values of 0 and 1 for the second and third parameters, respectively. If the function is called with only one argument, the other two arguments will be set to their default values.
• The programme then creates a basic class called Shape and adds a virtual function called draw (). A function that is declared in a base class and can be overridden by a derived class is referred to as a virtual function. In this instance, the draw() function is virtual, which means that any derived class may override it.
• The draw() function is then overridden in a derived class called Circle by the programme.Theoverride keyword is used to indicate that the function is intended to override a virtual function from the base class.
• In the main() function, the program calls the myFunction() function with different numbers of arguments, demonstrating how default arguments can make a function more flexible.
• The program then creates instances of the Shape and Circle classes using pointers, and calls the draw() function on each instance. The draw() function of the Circle class overrides the draw() function of the Shape class so that the output will be different for each instance.
• Finally, the program deletes the instances to avoid memory leaks.

Program Output:

Benefits of using Default Arguments with Virtual Functions

Flexibility: Default arguments can provide flexibility in the implementation of virtual functions. By providing default values for function arguments, developers can create functions that are more versatile and can be called in different ways depending on the specific requirements of the program.

Simplicity: Default arguments make it easier to use virtual functions in a way that makes sense for the specific use case.The code could be made more manageable and straightforward as a result.

Efficiency: Using default arguments in virtual functions can sometimes improve the performance of the program by allowing the compiler to optimize the code more effectively.

Drawback of using Default Arguments with Virtual Functions

Ambiguity: Using default arguments with virtual functions can sometimes create ambiguity in the code. When there are multiple functions with the same name, the compiler may be unable to determine which function to call if the arguments are not specified explicitly. This may cause the software to behave unexpectedly and include errors.

Complexity: While default arguments can simplify the code, they can also make it more complex and difficult to understand. This is especially true when the default arguments are not well documented or when they are changed over time.

Compatibility: Not all programming languages support default arguments with virtual functions. It may become more challenging to maintain and upgrade the code over time and its portability may be restricted as a result.

Conclusion

In conclusion, default arguments and virtual functions are two important features of C++ that can make code more flexible, efficient, and maintainable.

Default arguments allow you to specify default values for function parameters so they can be omitted when calling the function. This can help your code be clearer and simpler to comprehend, especially when working with functions that have a lot of parameters.

On the other hand, virtual functions let you specify a function in a base class that can be overridden by a derived class. This allows you to write more generic code that can be customized by different classes, which can make your code more reusable and easier to maintain.

When used together, default arguments and virtual functions can make your code even more powerful and flexible. For example, you can define a virtual function with default arguments in a base class, and then override it with different default arguments in a derived class. This can give you even more control over how your code behaves while allowing you to reuse common functionality.