Constructor and Destructor in C++

Constructor and Destructor in C++ are very important, without the help of Constructor we cannot invoke and it also helps us to do a lot of things

What is a Constructor ?

[A Constructor is a "special type of member function" which has the same name as of the "Class".]
[Constructor initialize the Objects in C++ and can be automatically called when an Object is created i.e, it's main purpose is to initialize all data-members of a Class, in other words to construct "Objects". ]
[A Constructor has no return-type although it is an Member-Function ( Functions that are written inside the "Class" is known as "Member-Function" ) ]

Example for Member-Function:-

class ABC {
     public:  //Access Specifier
     void Fun( ) //function having return-type➝ "void" 
    {
       .......
       .......
               }
}; 

Example for Constructor:-

 class ABC {
     public:  //Access Specifier
     ABC( ) //Constructor having "no return-type"
    {
      .......
      .......
              }
};

There are three types of Constructor :-

1. Default Constructor ─
   A Default Constructor is a constructor which has no argument, and if it has parameters then all the parameters has Default values. If their is not User-defined constructor inside the Class then the compiler automatically creates a Default Constructor.
   Example:-
   

    class ABC {
        public:  //Access Specifier
        int a,b; //Data-Members
        ABC( ) 
       {
        a=5; 
        b=10;
              }
   };
   
   int main()
   {
   ABC const; //here "const" is an Object
   cout<<"a:"<<const.a<<" b:"<<const.b; //to print 'a'&'b'
   }

   
      
   Output

   a:5 b:10




2. Parameterized Constructor ─
   Sometimes we need to pass arguments in a Constructor and it is possible. A Constructor which has arguments in it which is used to initialize different Data-Members and Member-Function inside a Class  is known as Parameterised Constructor.
   Example:-
   

    class ABC {
        public:  //Access Specifier
        int a,b; //Data-Members
        ABC(int x,int y) 
       {
          a=x;
          b=y;      
               }
   };
   
   int main()
   {
   ABC const; //here "const" is an Object
   const(10,20); 
   cout<<"a:"<<const.a<<" b:"<<const.b; //to print 'a'&'b'
   }

   
      
   Output

   a:10 b:20




3. Copy Constructor ─
   A Constructor which initialize an Object using another Object of the same Class
   In Simple ➝ If we have more than one Constructor in a single Class then one of the constructor is said to be a copy of another one.
   [ Note:- The parameters should be different between two Constructor which are of the same Class ]
   Example:-
   

    class ABC {
        public: 
        int a,b; //Data-Members of "int" type
        float a,b; //Data-Members of "float" type
   ABC(int x,int y) 
       {            //Parameter are "int" type
          a=x;
          b=y;      
               }
   ABC(float x,float y) 
       {                //Parameter are "float" type
          a=x;
          b=y;      
               }
   };
   
   int main()
   {
   int n,m;
   ABC const; //here "const" is an Object
   cin>>n>>m;
   const(n,m); 
   cout<<const.a<<const.b; //to print 'a'&'b'
   }

If 'n' & 'm' are of "int" type then the Constructor having the integer parameter will be executed but if the type of 'n' & 'm' is "float" then the Constructor having the float parameter will be executed.

What is a Destructor ?

[ Destructor are used to de-allocate the memory for a Class Object. ]
[ A Destructor is called automatically when an Object is destroyed or the Object passes out of the scope which has been created by the Constructor. ]
[ The name of the Destructor must start with the tilde character ( 〜 ). ]
[ Destructor has no return-type.  ]
[ Destructor also don't have any type of "parameters". ]
[ A Class can have only One-Destructor in it. Not more than one. ]

Example:-

class ABC{
        public: 
        ABC( )  //Constructor
        {
         cout<<"Constructor is called";
                    }
        ~ABC( )  //Destructor
        {
         cout<<"Destructor is called";
                    }
        void Mem_Fun( )  //Member-Function
        {
         cout<<"Member Function is called";
                    }
};

int main( )
{
 ABC obj;  //obj is the Object
 obj.Mem_Fun( ); //Member Function is called
 delete obj; //deleting the object
}

Output

Constructor is called
Member Function is called
Destructor is called

Introduction to Object-Oriented Programming language.

Introduction to C++.

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