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Learn about Declaration of a Copy Constructor

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. Here is a simple constructor class example below,

There are different constructor types in classes and the Copy Constructor is one of these. Copy Constructors not only used in classes but also used with struct and union data types Do you want to learn what is copy constructor or what kind of methods we have that we can declare and use copy constructors? In this post, we will try to explain how to use Copy Constructor with examples.

The Copy Constructor in classes (i.e class_name) is a non-template constructor whose first parameter is class_name&‍, const class_name&‍, volatile class_name&‍, or const volatile class_name&‍ . It can be used with no other parameters or with the rest of the parameters all have default values.

The Copy Constructor is a constructor type for classes that class_name must name the current class, or it should be a qualified class name when it is declared at namespace scope or in a friend declaration.

Typical Declaration of a Copy Constructor

Syntax to declare a Typical Copy Constructor,

Syntax to use Copy Constructor, this copy source_class to new_class as below,

An example with a class;

and the output will be,

As you see, this copy constructor copies only class properties and methods but not values of it. To copy values of parameters (attributes) of classes we should add each parameter into copy constructor and set them as below,

Thus, by adding this line full Copy Constructor example can be like this,

Now, this copy constructor copies not only class properties and methods but also copies values defined by user. Result will be as follows,

Both methods can be used, if you don’t need to copy to each values of properties of the source class to the destination class, and you will set each parameters with new values use the first example, it will be faster. If you need to copy some or all parameter values then you can use the last example here.

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About author

33+ years of coding with more than 30+ programming languages, mostly C++ on Windows, Android, Mac-OS, iOS, Linux and some other operating systems. Dr. Yilmaz Yoru was born in 1974, Eskisehir-Turkey. He graduated from the department of Mechanical Engineering of Eskisehir Osmangazi University in 1997. One year later he started to work in the same university as an assistant. He received his MSc and PhD degrees from the same department of the same university. He has married and he is a father of a son. Some of his interests are Programming, Thermodynamics, Fluid Mechanics and Artificial Intelligence. He also likes the graphical 2D & 3D design and high-end innovations.
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