Constructors in C++

• It is a member function having the same name as it’s class and which is used to initialize the objects of that class type with a legal initial value.
• The compiler call's the constructor when an object is created.
• We can't define a constructor in the private section, we can define only it in the public section.

Characteristics of constructors

• A constructor takes the same name as the class name.
• We can define our own constructors.
• Automatically called when an object is created.
• No return type is specified for the constructor.
• Overloading of constructors is possible.
• They cannot be inherited.
• They cannot be static.

Defining a constructor

• The constructor can be defined inside the class and also outside the class.

Defining a constructor(Inside the class)

        class class-name{
           access label:
           data members;
           member functions;
           class-name();//constructor
        }

Example

        class employee{
           private:
           int employee_id;
           char name[20];
           float salary;
           public:
           employee(){
             employee_id=10;
             strcpy(name, “ashok’’);
             salary=5000;
           }
           void getdata();
        }ob1,ob2;

Defining the constructor(Outside the class)

        class-name::class-name
        {
           body of the constructor function;
        }

Types of constructor

1. Default Constructor
2. Parameterized Constructor
3. Copy Constructor

Default Constructor

• The constructor which has no arguments on it is known as default constructor.
• The default constructor is also known as a no-argument constructor.

Example

        class creature{
           private:
           int yearofbirth;
           public:
           creature(){
            cout<<"constructor called";
           };
           main(){
           creature obj;
           getch();
           return 0;
        }

Parameterized constructor

• A constructor that receives arguments/parameters, is called the parameterized constructor.
• We can pass arguments to the constructor when objects are created.

Example

        class creature{
           private:
           int yearofbirth;
           public: 
           creature(int year){
             year=yearofbirth;
           }
        };

copy constructor

• A constructor that initializes an object using values of another object passed to it as the parameter, is called copy constructor.
• It creates a copy of the passed object.

Example

         class abc{
           int a;
           float b; 
           public:
           void fun();
           abc(int x, float y){
              a=x;
              b=y;
           }
           abc(abc &dob){
              a=dob.a;
              b=dob.b;
           }
          };