static constructor c++ code example

Example 1: static class in C++

#include <iostream>
 
using namespace std;

class Box {
   public:
      static int objectCount;
      
      // Constructor definition
      Box(double l = 2.0, double b = 2.0, double h = 2.0) {
         cout <<"Constructor called." << endl;
         length = l;
         breadth = b;
         height = h;

         // Increase every time object is created
         objectCount++;
      }
      double Volume() {
         return length * breadth * height;
      }
      static int getCount() {
         return objectCount;
      }
      
   private:
      double length;     // Length of a box
      double breadth;    // Breadth of a box
      double height;     // Height of a box
};

// Initialize static member of class Box
int Box::objectCount = 0;

int main(void) {
   // Print total number of objects before creating object.
   cout << "Inital Stage Count: " << Box::getCount() << endl;

   Box Box1(3.3, 1.2, 1.5);    // Declare box1
   Box Box2(8.5, 6.0, 2.0);    // Declare box2

   // Print total number of objects after creating object.
   cout << "Final Stage Count: " << Box::getCount() << endl;

   return 0;
}

Example 2: why constructor can't be static in c++

static variable are those variable declared with static and i will be refer to the common property of all the objects in a java and it is mainly used for memory managment in java. constructor is used to inilialize the objects and it is automatically called at time of object creation.

It is not possible in the constructor because static member variables are not associated with each object of the class. It is shared by all objects. If you initialize the static variable into the constructor then it means that you are trying to associate with a particular instance of class. Since this is not possible, it is not allowed.