Constructor in C++

-

Constructor:

                Constructor is a special type of member function that is automatically called when an object of the class is created to whom the constructor belongs.
Properties of constructor:
  • A constructor initializes an object as soon as it is created.
  • Constructor name is same as class name and it doesn't have a return type.
      class A 
       {
       public:
              A ( )    // constructor of class A
                {
                  // object initialization
                 }
        };

Constructors can be defined either inside the class definition or outside class definition using class name and scope resolution :: operator.

Uses of constructor:

Constructor are Used Because the memory used by Classes can't be released.
But in case of constructor the memory used by the constructor can be freed by using a special member function ,which is known as destructor. This is the basic purpose of constructors in c++.


☝ Make it clear that whether you define a constructor or not a constructor always exist and is called whenever you create an object of the class.

Types of constructor:

Constructors are of three types:
  1. Default Constructor
  2. Parameterized Constructor
  3. Copy Constructor

Default Constructors:

Default constructor is the constructor which doesn't take any argument. It has no parameter.

Syntax:
class_name ()
{
// constructor definition
}
Example:
class Demo {
       public:
               int obj;
               Demo (){
               obj=10;        // object initialization
}
};
  int main (){
        Demo c;
        cout << c.obj;
}
Output:
   10

In this case, as soon as the object is created the constructor is called which initializes its data members.

A default constructor is so important for initialization of object members, that even if we do not define a constructor explicitly, the compiler will provide a default constructor implicitly.

Parameterized Constructor :

                             A constructor is called Parameterized Constructor when it accepts a specific number of parameters. To initialize data members of a class with distinct values.

Example:
#include  <iostream>
using namespace std;
     class Demo {
           public:
               int obj;
              Demo (int a){
              obj=a;
}
         };
   int main (){
         Demo a(4);
         Demo b(5);
         Demo c(6);
         cout << a.obj <<endl;
         cout << b.obj <<endl;
         cout << c.obj <<endl
        return 0;
Output:
   4
   5
   6

Copy Constructor:
                                         These are special type of Constructors which takes an object as argument, and is used to copy values of data members of one object into other object.

Example:

#include<iostream>
using namespace std;
  
class Point
{
private:
    int x, y;
public:
    Point(int x1, int y1) { x = x1; y = y1; }
  
    // Copy constructor
    Point(const Point &p2) {x = p2.x; y = p2.y; }
  
    int getX()            {  return x; }
    int getY()            {  return y; }
};
  
int main()
{
    Point p1(10, 15); // Normal constructor is called here
    Point p2 = p1; // Copy constructor is called here
  
    // Let us access values assigned by constructors
    cout << "p1.x = " << p1.getX() << ", p1.y = " << p1.getY();
    cout << "\np2.x = " << p2.getX() << ", p2.y = " << p2.getY();
  
    return 0;
}

Output:

p1.x = 10, p1.y = 15
p2.x = 10, p2.y = 15

Watch a quick editorial here:


Comments

Post a Comment

Popular posts from this blog

Virtual function in c++

-
Virtual Function: Virtual means existing in effect but not in reality. A type of function that appears to exist in some part of the program but does not exist really is called a virtual function. Virtual functions are used to implement polymorphism. They enable the user to execute completely different functions by the same function call. A virtual function is defined in the parent class and is overridden in child classes. It is defined by the keyword virtual. If you want to call a virtual function in C++ and execute the redefined version of the member function, you can achieve this task using a pointer or a reference ( -> ) by referring a derived class object to the base class. A base class pointer has the capability to point to the objects of the base class and the derived class. But it's converse is not true. An example of using virtual function with reference: #include<iostream> using namespace std; class Animal {     public:         virtual ...
Read more

Multiple, Multilevel, Hybrid and Hierarchical inheritance

-
Image
Multiple inheritance:                          Multiple inheritance is a type of inheritance in c++ in which a class can be inherited from more than one classes. In this case the inherited class has more than one parent class. Multiple inheritance example:         #include <iostream> using namespace   std; class Animal { public:    Animal(){ cout<<" Animal's constructor "<<endl;} }; class Mammal { public:    Mammal(){cout<<" Mammal's constructor "<<endl;} }; class Bat : public Animal,public Mammal { public:   Bat(){ cout<<" Bat's constructor "<<endl;} }; int main(){     Bat bat1;    return 0; } Output: Animal's constructor Mammal's constructor Bat's constructor Multilevel inheritance:            In multilevel inheritance a class can be derived from another class who is already def...
Read more

Practice problem classes and objects.

-
        Creating classes and objects in C++ Problem:        Create a class named ClassRoom  that has 6 private  member variables named t otalChairs, totalTables, classGrade, teacherName, totalStudents and  classRep. Your class must have 2  public member functions named as input and  output. These two input and output functions will work as getter and setter. You must also create a constructor that initializes the values of all the private member variables to null or 0. Remember: We can use any name for our getter and setter function. Now for our main method create an object of our class ClassRoom named Class1. Input values from the user by calling the Input function of the object Class1. Then output all the values. All the above conditions must be fulfilled. Visit here for reference about classes and objects: C++ classes and objects
Read more