Answer to Question #327053 in C++ for Pragnan

Question

What are the various types of constructors used in object oriented programming? Explain with an example.

Answer 1

1) Default Constructor in C++

• The default constructor is the constructor which doesn’t take any argument. It has no parameters.
• 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 the initialization of object members, that even if we do not define a constructor explicitly, the compiler will provide a default constructor implicitly.

Sample Code:

#include<iostream>
using namespace std;

class construct { 
    public: 
    int a, b; 
  
    // Default Constructor 
    construct() 
    { 
        a = 10; 
        b = 20; 
    } 
};

int main() 
{ 
    construct c; 
    int sum = c.a + c.b;
  
    cout << "a : " << c.a << endl;
    cout << "b : " << c.b << endl;
    cout << "sum : " << sum << endl; 
    
    return 0; 
}

2) Parameterized Constructor in C++

• Arguments can be passed to the parameterised constructors.
• These arguments help initialize an object when it is created.
• To create a parameterized constructor, simply add parameters to it the way you would to any other function.
• When you define the constructor’s body, use the parameters to initialize the object.

Sample Code:

#include<iostream>
using namespace std;

class PrepInsta { 
    private: 
    int a, b;
    
    public: 
    
    PrepInsta(int a1, int b1) 
    { 
        a = a1; 
        b = b1; 
    } 
  
    int getA() 
    { 
        return a; 
    } 
  
    int getB() 
    { 
        return b; 
    } 
};

int main() 
{ 
  PrepInsta obj1(10, 15);
  
  cout << "a = " << obj1.getA() << ", b = " << obj1.getB(); 
  
  return 0; 
}

3) Copy Constructor in C++

• A copy constructor is a member function which initializes an object using another object of the same class.
• Whenever we define one or more non-default constructors( with parameters ) for a class, a default constructor( without parameters ) should also be explicitly defined as the compiler will not provide a default constructor in this case.
• An object can be initialized with another object of same type. This is same as copying the contents of a class to another class.
• For a better understanding of Copy Constructor in C++ (click here).

Sample code:

#include<iostream>
using namespace std;
class PrepInsta 
{ 
private: 
    int x, y; 
public: 
    PrepInsta()
    { // empty default constuctor
    }
    
    PrepInsta(int x1, int y1) 
    { 
        x = x1; 
        y = y1;

        cout << "Parameterized constructor called here" << endl;

    } 

    // User defined Copy constructor 
    PrepInsta(const PrepInsta &p2) 
    {
        x = p2.x; 
        y = p2.y; 
        cout << "Copy constructor called here" << endl;
    } 

    int getX()            
    {  
        return x; 

    } 
    int getY()            
    {  
        return y; 

    } 
}; 

int main() 
{ 
    // Trying to call parameterized constructor here
    PrepInsta p1(10, 15); 
    
    // Trying to call copy constructor here 
    PrepInsta p2 = p1; 
    
    // Trying to call Copy constructor here (Another way of doing so)
    PrepInsta p3(p1);
    PrepInsta p4;
 
    // Here there is no copy constructor called only assignment operator happens
    p4 = p1;
    
    cout << "\nFor p4 no copy constructor called only assignment operation happens\n" << endl;

    // displaying values for both constructors 
    cout << "p1.x = " << p1.getX() << ", p1.y = " << p1.getY();
    cout << "\np2.x = " << p2.getX() << ", p2.y = " << p2.getY(); 

    cout << "\np3.x = " << p3.getX() << ", p3.y = " << p3.getY(); 
    cout << "\np4.x = " << p4.getX() << ", p4.y = " << p4.getY();
    
    return 0; 
}