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Learn Definition of the Default Constructor Outside of a Class Definition

The Constructor in C++ is a function, a method in the class, but it is a ‘special method’ that is automatically called when an object of a class is created. We don’t need to call this function. Whenever a new object of a class is created, the Constructor allows the class to initialize member variables or allocate storage. This is why the name Constructor is given to this special method.

There are different contractor types and the Default Constructor in classes is one of these. This method is not only used in classes but also used with struct and union data types A Default Constructor is a constructor type in Classes that is called when class is defined with no arguments, or it is defined with an empty parameter list, or with default arguments provided for every parameter. A type with a public default constructor is Default Constructible;

Do you want to learn how we define a Default Constructor Outside of a Class? In the definition of a default Constructor, class_name must name the current class or current instantiation of a class template. It must be a qualified class name when declared at namespace scope or in a friend declaration. Here are examples;

Definition of the Default Constructor Outside of a Class Definition

We can define a default constructor outside of a class. Add a class name and ( ); inside the class also add class name and :: operator with class name and ( ) outside of that class as below,

Syntax,

An example with a class;

Here is a full example about how a Constructor defined outside of a class. Here we just create a new test object, and it automatically sets x=100 and calls constructor method.

Note that here x is defined in the first class and it is used in the Definition of the Default Constructor Outside of a Class Definition. The output will be as here,

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About author

Dr. Yilmaz Yoru has 33+ years of coding with more than 30+ programming languages, mostly C++ on Windows, Android, Mac-OS, iOS, Linux, and some other operating systems. He was born in 1974, Eskisehir-Turkey, started coding in college and graduated from the department of Mechanical Engineering of Eskisehir Osmangazi University in 1997. He worked as a research assistant at the same university for more than 10 years. He received his MSc and PhD degrees from the same department at the same university. Since 2012, he is the founder and CEO of Esenja LLC Company. He has married and he is a father of a son. Some of his interests are Programming, Thermodynamics, Fluid Mechanics, Artificial Intelligence, 2D & 3D Designs, and high-end innovations.
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