In Chapter 6, we described two types of variables: automatic and static. Recall that if a local variable of a function is static, it exists between function calls. Similar to static variables, a class can have static members, functions, or variables.
If a function of a class is static, in the class definition it is declared using the keyword static in its heading.
If a member variable of a class is static, it is declared using the keyword static,
A public static member, function, or variable of a class can be accessed using the class name and the scope resolution operator.
In C++, a static class member is a member of a class that belongs to the class itself, rather than to any particular instance of the class. A static member is shared by all objects of the class and can be accessed using the class name, without needing an object of the class.
Here's an example of a static class member:
class MyClass {
public:
static int count; // static class member
MyClass() {
count++; // increment count on each object creation
}
};
int MyClass::count = 0; // initialize the static member outside the class definition
int main() {
MyClass obj1;
MyClass obj2;
MyClass obj3;
cout << MyClass::count << endl; // prints "3"
return 0;
}
In this example, we have defined a static class member count in the MyClass class. We have also defined a constructor that increments count on each object creation. Finally, we have initialized the static member outside the class definition.
In the main function, we create three objects of the MyClass class, which results in count being incremented three times. We then print the value of count using the class name, without needing an object of the class.
Static class members are useful when you need to share data or behavior among all objects of a class. They can also be used to maintain a count of objects of a class, as shown in this example.