static variable c++ class code example

Example 1: static variable in c++

/*
this example show where and how
static variables are used
*/

#include <iostream>
#include <string>

//doing "using namespace std" is generally a bad practice, this is an exception
using namespace std;

class Player
{
  int health = 200;
  string name = "Name";
  
  //static keyword
   static int count = 0;
public:
  //constructor
  Player(string set_name)
    :name{set_name}
  {
    count++;
  }
  
  //destructor
  ~Player()
  {
    count--;
  }
  
  int how_many_player_are_there()
  {
    return count;
  }
  
};

int main()
{
  Player* a = new Player("some name");
  cout << "Player count: " << *a.how_many_player_are_there() << std::endl;
  
  Player* b = new Player("some name");
  cout << "Player count: " << *a.how_many_player_are_there() << std::endl;
  
  delete a;
  
  cout << "Player count: " << *b.how_many_player_are_there() << std::endl;
}

/*output:
1
2
1
*/

Example 2: 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;
      }
      
   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) {
   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.
   cout << "Total objects: " << Box::objectCount << endl;

   return 0;
}