C++Builder Learn about Declaration of a Default Constructor Inside of Class Definition

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Learn about Declaration of a Default Constructor Inside of Class Definition
By Yilmaz Yoru June 12, 2021

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.

class myclass
{         
  public:   
    myclass()
    {
       std::cout << "myclass is constructed!\n";
    };
};

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 to declare a Default Constructor Inside of Class Definition? 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 below how we declare;

Declaration of a Default Constructor Inside of Class Definition​

We can declare a default constructor inside of a class. Just add class name with ( and )inside that class as below; create a method

Syntax,

class_name()
{
};

An example of Declaration of a Default Constructor Inside of Class Definition with a class as follows,

class myclass
{         
  public:   
    myclass()
    {
    };
}

This is a full example how a Constructor work in a class. Here we just create a new test object, and it automatically sets x=100 and calls constructor method.

#include <iostream>
 
class myclass
{
  public:
 int x = 0;
 
 myclass()
 {
 x = 100;
 std::cout << "I am constructed\n";
 };
};
 
int main()
{
 class myclass test;
 
 std::cout << test.x << '\n';
 
 getchar();
 
 return 0;
}

And the output will be:

I am constructed
100