Whenever we create an object of a class, the default constructor of that class is invoked automatically to initialize the members of the class.
If we inherit a class from another class and create an object of the derived class, it is clear that the default constructor of the derived class will be invoked but before that the default constructor of all of the base classes will be invoke, i.e the order of invokation is that the base class’s default constructor will be invoked first and then the derived class’s default constructor will be invoked.
Why the base class’s constructor is called on creating an object of derived class?
To understand this you will have to recall your knowledge on inheritance. What happens when a class is inherited from other? The data members and member functions of base class comes automatically in derived class based on the access specifier but the definition of these members exists in base class only. So when we create an object of derived class, all of the members of derived class must be initialized but the inherited members in derived class can only be initialized by the base class’s constructor as the definition of these members exists in base class only. This is why the constructor of base class is called first to initialize all the inherited members.
Inside base class Inside sub class
Order of constructor call for Multiple Inheritance
For multiple inheritance order of constructor call is, the base class’s constructors are called in the order of inheritance and then the derived class’s constructor.
Inside first base class Inside second base class Inside child class
Order of constructor and Destructor call for a given order of Inheritance
How to call the parameterized constructor of base class in derived class constructor?
To call the parameterised constructor of base class when derived class’s parameterised constructor is called, you have to explicitly specify the base class’s parameterised constructor in derived class as shown in below program:
Inside base class's parameterised constructor Inside sub class's parameterised constructor
- Whenever the derived class’s default constructor is called, the base class’s default constructor is called automatically.
- To call the parameterised constructor of base class inside the parameterised consructor of sub class, we have to mention it explicitly.
- The parameterised constructor of base class cannot be called in default constructor of sub class, it should be called in the parameterised constructor of sub class.
Destructors in C++ are called in the opposite order of that of Constructors.
This article is contributed by Abhirav Kariya and Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
Don’t stop now and take your learning to the next level. Learn all the important concepts of Data Structures and Algorithms with the help of the most trusted course: DSA Self Paced. Become industry ready at a student-friendly price.
- Is it possible to call constructor and destructor explicitly?
- Difference Between Constructor and Destructor in C++
- Calling virtual methods in constructor/destructor in C++
- __attribute__((constructor)) and __attribute__((destructor)) syntaxes in C
- Difference between Call by Value and Call by Reference
- Private Destructor
- Virtual Destructor
- Pure virtual destructor in C++
- A C/C++ Function Call Puzzle
- Can we call an undeclared function in C++?
- Constructor Overloading in C++
- Constructor Delegation in C++
- Copy Constructor in C++
- What is conversion constructor in C++?
- Can a constructor be private in C++ ?
- How to create a List with Constructor in C++ STL
- Passing a vector to constructor in C++
- Dynamic Constructor in C++ with Examples
- Advanced C++ | Virtual Constructor
- When should we write our own copy constructor?