Answer to Question #228147 in C++ for Arup

Question

Static data members of a class occupy memory once whereas non static data members occupy members as per the number of objects created. Justify the statement by writing a program.

Answer 1

When a member of class is declared as static, we only have a copy of the static member regardless of number of objects created as illustrated by the following c++ program

#include <iostream>
 
using namespace std;


class My_Box {
   public:
      static int numOfObjects;
      
      // Here, you create a constructor having same name as the class
      My_Box(float l = 1.0, float w = 1.0, float h = 1.0) {
         cout <<"The Constructor call to initialize objects as they are created   " << endl;
         length = l;
         width = w;
         height = h;
         
         // The numOfObjects increments at every time an object is created 
         numOfObjects++;
      }
      float Volume() {
         return length * width * height;
      }
      
   private:
      float length;    
      float width;    
      float height;     
};


// Initialization of class static member of class 
int My_Box::numOfObjects = 0;


int main(void) {
   My_Box FirstBox(2.1, 6.2, 1.5);    
  My_Box SecondBox(11.5, 5.5, 2.0);   


   // Display sum of objects created.
   cout << "Total objects: " << My_Box::numOfObjects << endl;


   return 0;
}

On the other hand, non static data members occupy members as per the number of objects created as illustrated by the program bellow

#include <iostream>


class NonStaticDemo
{
private:
	int x { 5 };    // << wow!
	int y { 5 };    // << wow2!
	std::string Myname { "Sample namee" }; // wow3!


public:
	NonStaticDemo() {
		std::cout << "NonStaticDemo   {" << x << ", " << y << ", \"" << Myname << "\"}\n";
	}


	~NonStaticDemo() { std::cout << "NonStaticDemo::destructor\n"; }
};


int main()
{
	NonStaticDemo sampleObject;
}