Static Members of a C++ Class

Static Members of a Class

We can define class members static using static keyword. When we declare a member of a class as static it means no matter how many objects of the class are created, there is only one copy of the static member.

A static member is shared by all objects of the class. All static data is initialized to zero when the first object is created, if no other initialization is present. We can't put it in the class definition but it can be initialized outside the class as done in the following example by redeclaring the static variable, using the scope resolution operator :: to identify which class it belongs to.

Example

Let us try the following example to understand the concept of static data members −

 #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; } 

When the above code is compiled and executed, it produces the following result −

 Constructor called. Constructor called. Total objects: 2 

Static Function Members

By declaring a function member as static, you make it independent of any particular object of the class. A static member function can be called even if no objects of the class exist and the static functions are accessed using only the class name and the scope resolution operator ::.

A static member function can only access static data member, other static member functions and any other functions from outside the class.

Static member functions have a class scope and they do not have access to the this pointer of the class. You could use a static member function to determine whether some objects of the class have been created or not.

Example

Let us try the following example to understand the concept of static function members −

 #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; } 

When the above code is compiled and executed, it produces the following result −

 Inital Stage Count: 0 Constructor called. Constructor called. Final Stage Count: 2 

Use Cases for Static Members

Here are the following use cases:

• A singleton pattern is a design pattern that makes sure that a class has only one instance and provides a global point of access to it. Here static members are perfect for implementing this pattern because they allow to maintenance of a single shared instance of the class.
  
• Static members are often used to manage shared resources or counters that should be shared across all instances of a class.
  
• Static members can be used to store global configuration settings or constants, useful for managing a pool of resources (e.g., a cache, database connection pool, etc.) and implementing a logging system that is shared across instances. which is shared across all instances of a class.
  
• Static members can be used for Tracking Method calls.