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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

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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