static variables c++ 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 inside local scope in c++

#include<iostream>
//Singleton class is a class having only one instance
class SingleTon {

public:
	static SingleTon& Get() {
		static SingleTon s_Instance;
		return s_Instance;
	}//there is only one instance of static functions and variables across all instances of class
	void Hellow() {}
};
void Increment() {
	int i = 0;//The life time of variable is limited to the function scope
	i++;
	std::cout << i << std::endl;
};//This will increment i to one and when it will reach the end bracket the lifetime of var will get  destroyed
void IncrementStaticVar() {
	static int i = 0;//The life time of this var is = to program
	i++;
	std::cout << i << std::endl;
}//This will increment i till the program ends
int main() {
	
	Increment();//output 1
	Increment();//output 1
	Increment();//output 1
	IncrementStaticVar();// output 2
	IncrementStaticVar();// output 3
	IncrementStaticVar();// output 4
	IncrementStaticVar();// output 5
	SingleTon::Get();
	std::cin.get();

}

Example 3: static in class c++

#include <iostream>

class Entity {
public:
	static int  x,y;
	static void Print() {
		std::cout << x << ", " << y << std::endl;
	}// sta1tic methods can't access class non-static members
};
int Entity:: x;
int Entity:: y;// variable x and y are just in a name space and we declared them here
int main() {
	Entity e;
	Entity e1;
	e.x = 5;
	e.y = 6;
	e1.x = 10;
	e1.y = 10;
	e.Print();//output => 10 because variable x and y being static point to same block of memory
	e1.Print();//output => 10 because variable x and y being static point to same block of memory
	Entity::x;	//you can also acess static variables and functions like this without creating an instance
    Entity::Print();	//you can also acess static variables and functions like this without creating an instance
	std::cin.get();
}

Example 4: 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;
}