Constructor in C++

Constructor:

• A constructor is one kind of feature in oops.
• Constructor means, class name the same as the function or method name.
• It is similar to the function so it’s called special member function and that class name the same as the constructor name.
• It used to construct and initialize all the data members.
• Constructor automatically called, when the object is created.
• It can be defined inside the class and definitions are outside the class definition help of the class name.         

Special characteristics of the constructor:

• A constructor should be declared in the public section.
• The name should be equal to the class name followed by the parenthesis.
• It does not have any return type, not even void.
• They cannot be inherited through a derived class can call the base class constructor.
• It cannot be a virtual function.

Types of constructor:

• Three different types of constructors:

1. Default constructor
2. Parameterized constructor
3. Copy constructor

Default constructor:

• A constructor with no parameters is known as a default constructor.

Syntax:

1. class class_name
   {
   Data members;
   Access specifiers:
   class_name ()
   {
             //Statements
   }
   }; 

Example:

1. #include<iostream.h>
   #include<conio.h>
   class addition
   {
   int a,b;
   public:
   addition()//no parameter with constructor
   {
   cout<<"\n Enter a and b value: ";
   cin>>a>>b;
   cout<<"\n Addition value is:"<<a+b;
   }
   };
   void main()
   {
   clrscr();
   addition obj;//object creation
   getch();
   }

Output:

Parameterized constructor:

• A constructor with parameters is known as a parameterized constructor.

Syntax:

1. class class_name
   {
   Data members;
   Access specifiers:
   class_name (parameter list)
   {
             //Statements
   }
   }; 

Example:

1. #include<iostream.h>
   #include<conio.h>
   class std
   {
   int roll_num,mark;
   char *name[10];
   public:
   std(int x,char *y,int z)
   {
   roll_num=x;
   *name=y;
   mark=z;
   cout<<"\n Roll Number\t Student Name\t Student total mark\n";
   cout<<"\n "<<roll_num<<"\t\t "<<*name<<"\t\t "<<mark<<endl;
   }
   };
   void main()
   {
   clrscr();
   std s1(01,"Ahamed",455);
   std s2(02,"Banu",344);
   getch();
   }

Output:

Copy constructor:

• It is used when one object of class initializes another object.
• It takes a reference to an object of the same class as an argument.

Syntax:

1. Classname(const class_name & object_name
   {
             variable_name=object_name.constructor_variable;
   }
   Object creation:

   class_name object_name1;

   Method 1:

   class_name object_name2=object_name1;

   Method 2:

   
   

   class_name object_name2(object_name1);

Example:

1. #include<iostream.h>
   #include<conio.h>
   class copy_num
   {
   int a, b;
   public:
   copy_num(int x, int y)
   {
   a = x;
   b = y;
   cout << "\n Assigned parameter values to the data member.";
   }
    copy_num(const copy_num& obj)
    {
   a = obj.a;
   b = obj.b;
   cout << "\n Copied the value in constructor.";
   }
   void show()
   {
   cout << "\n Values of a and b value is: \t" << a << "\t" << b;
   }
   };
   void main() {
   clrscr();
   copy_num obj(4,6);
   //Copy Constructor Invoked - Method 1
   copy_num obj2(obj);
   //Copy Constructor Invoked - Method 2
    copy_num obj3 = obj;
    obj.show();
   obj2.show();
   obj3.show();
   getch();
   }

Output:

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