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C++ OOP
course content

Course Content

C++ OOP

C++ OOP

1. Fundamentals of OOP in C++
Introduction to Object-Oriented Programming in C++Why use Object-Oriented Programming?Class Creation SyntaxAttributes of the ClassMethods of the ClassStatic Members of The ClassThe This KeywordClasses and Objects Overview
2. Constructors and Destructors
What is a Constructor of the ClassConstructor and AttributesConstructor Initialization ListInitialization List PracticeConstructor DelegationConstructor Delegation PracticeWhat is a Destructor of the ClassConstructors and Destructors Practice
3. Encapsulation Overview
Introduction to EncapsulationAccess Modifiers KeywordsAccess Modifiers PracticeAccessor and Mutator MethodsSegmentation and AggregationThe Friend Keyword
4. Inheritance Overview
Introduction to InheritanceAccess Modifiers in InheritanceMulptiple InheritanceConstructor and Destructor in InheritanceDiamond InheritanceThe Final Keyword
5. Polymorphism Overview
Introduction to PolymorphismVirtual and Override KeywordsPure Virtual MethodOperator Overloading

book
Virtual and Override Keywords

Virtual Keyword

The virtual keyword is used before a method declaration in a class to solve the issue we discussed earlier. It's employed for methods that are common among all subclasses but require distinct implementations for each. Essentially, it looks like any other method declaration, except it begins with virtual.

Base.h

Base.h

copy

              
1234567

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

When a function is declared as virtual in a superclass, it allows it to be overridden in a subclass. This means the subclass can provide its own implementation, which will be invoked instead of the original implementation when the function is called through a pointer or reference to the superclass.

main.cpp

main.cpp

copy

              
123456789101112131415161718192021222324252627

            
#include <iostream>

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


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

int main()
{
    Base* obj;
    Derived derived;
    
    obj = &derived;
    obj->display();
}
Note
Note

When you have a pointer to an object and you want to access its members through the pointer, you use the arrow operator (->).

Returning to the solution for the original problem with buttons, this method enables us to easily create a single function that takes a parent Button pointer as a parameter. Consequently, we can invoke this function by passing a SubmitButton, ResetButton, or CancelButton, and it will behave as intended.

main.cpp

main.cpp

copy

              
12345678910111213141516171819202122232425262728293031

            
#include <iostream>

class Button {
public:
    virtual void onClick() { std::cout << "Click" << std::endl; }
};

class UploadButton : public Button {
public:
    void onClick() { std::cout << "Upload" << std::endl; }  
};

class ResetdButton : public Button {
public:
    void onClick() { std::cout << "Reset" << std::endl; }  
};

class CancelButton : public Button {
public:
    void onClick() { std::cout << "Cancel" << std::endl; }  
};

void user_clicked_button(Button& btn) {
    btn.onClick();
}

int main()
{
    UploadButton uploadButton;
    user_clicked_button(uploadButton);
}
Note
Note

Try to create objects of different subclasses and pass them to the function.

The Override Keyword

The override keyword is used in a subclass to explicitly indicate that a member function overrides a virtual function from a superclass. It helps catch errors at compile time if the function signature in the subclass does not match any virtual function in the superclass.

main.cpp

main.cpp

copy

              
1234567891011121314

            
#include <iostream>

class Button {
public:
    virtual void handleClick() { std::cout << "Click" << std::endl; }
};

class UploadButton : public Button {
public:
    // marked override, but does not override
    void onClick() override { std::cout << "Upload" << std::endl; }  
};

int main() { }

If there's a mistake, such as a typo in the function signature or the superclass does not have the function you're attempting to override, the compiler will generate an error, helping to catch potential bugs at compile time. This feature is especially useful in large team environments, where tracking changes like method renaming can be challenging.

question mark

What is the main purpose of the virtual keyword?

Select the correct answer

Everything was clear?

How can we improve it?

Thanks for your feedback!

SectionΒ 5. ChapterΒ 2

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course content

Course Content

C++ OOP

C++ OOP

1. Fundamentals of OOP in C++
Introduction to Object-Oriented Programming in C++Why use Object-Oriented Programming?Class Creation SyntaxAttributes of the ClassMethods of the ClassStatic Members of The ClassThe This KeywordClasses and Objects Overview
2. Constructors and Destructors
What is a Constructor of the ClassConstructor and AttributesConstructor Initialization ListInitialization List PracticeConstructor DelegationConstructor Delegation PracticeWhat is a Destructor of the ClassConstructors and Destructors Practice
3. Encapsulation Overview
Introduction to EncapsulationAccess Modifiers KeywordsAccess Modifiers PracticeAccessor and Mutator MethodsSegmentation and AggregationThe Friend Keyword
4. Inheritance Overview
Introduction to InheritanceAccess Modifiers in InheritanceMulptiple InheritanceConstructor and Destructor in InheritanceDiamond InheritanceThe Final Keyword
5. Polymorphism Overview
Introduction to PolymorphismVirtual and Override KeywordsPure Virtual MethodOperator Overloading

book
Virtual and Override Keywords

Virtual Keyword

The virtual keyword is used before a method declaration in a class to solve the issue we discussed earlier. It's employed for methods that are common among all subclasses but require distinct implementations for each. Essentially, it looks like any other method declaration, except it begins with virtual.

Base.h

Base.h

copy

              
1234567

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

When a function is declared as virtual in a superclass, it allows it to be overridden in a subclass. This means the subclass can provide its own implementation, which will be invoked instead of the original implementation when the function is called through a pointer or reference to the superclass.

main.cpp

main.cpp

copy

              
123456789101112131415161718192021222324252627

            
#include <iostream>

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


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

int main()
{
    Base* obj;
    Derived derived;
    
    obj = &derived;
    obj->display();
}
Note
Note

When you have a pointer to an object and you want to access its members through the pointer, you use the arrow operator (->).

Returning to the solution for the original problem with buttons, this method enables us to easily create a single function that takes a parent Button pointer as a parameter. Consequently, we can invoke this function by passing a SubmitButton, ResetButton, or CancelButton, and it will behave as intended.

main.cpp

main.cpp

copy

              
12345678910111213141516171819202122232425262728293031

            
#include <iostream>

class Button {
public:
    virtual void onClick() { std::cout << "Click" << std::endl; }
};

class UploadButton : public Button {
public:
    void onClick() { std::cout << "Upload" << std::endl; }  
};

class ResetdButton : public Button {
public:
    void onClick() { std::cout << "Reset" << std::endl; }  
};

class CancelButton : public Button {
public:
    void onClick() { std::cout << "Cancel" << std::endl; }  
};

void user_clicked_button(Button& btn) {
    btn.onClick();
}

int main()
{
    UploadButton uploadButton;
    user_clicked_button(uploadButton);
}
Note
Note

Try to create objects of different subclasses and pass them to the function.

The Override Keyword

The override keyword is used in a subclass to explicitly indicate that a member function overrides a virtual function from a superclass. It helps catch errors at compile time if the function signature in the subclass does not match any virtual function in the superclass.

main.cpp

main.cpp

copy

              
1234567891011121314

            
#include <iostream>

class Button {
public:
    virtual void handleClick() { std::cout << "Click" << std::endl; }
};

class UploadButton : public Button {
public:
    // marked override, but does not override
    void onClick() override { std::cout << "Upload" << std::endl; }  
};

int main() { }

If there's a mistake, such as a typo in the function signature or the superclass does not have the function you're attempting to override, the compiler will generate an error, helping to catch potential bugs at compile time. This feature is especially useful in large team environments, where tracking changes like method renaming can be challenging.

question mark

What is the main purpose of the virtual keyword?

Select the correct answer

Everything was clear?

How can we improve it?

Thanks for your feedback!

SectionΒ 5. ChapterΒ 2
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