14.5 Static Member Functions

The member variable stack_count is defined as private. This means that nothing outside the class can access it. You want to know how many stacks are defined, so you need a function to get the value of stack_count. A first cut might be:

class stack {
        static int stack_count; // Number of stacks currently in use
        // ... member variables
    public:
        // Not quite right
        int get_count(  ) {
            return (stack_count);
        }        
        // ... other member functions
};

This works, but you need a stack type variable to access this function.

{
    stack temp_stack;    // Stack for getting the count
    std::cout << "Current count " << temp_stack.get_count(  ) << '\n';
}

Because get_count doesn't use any nonstatic data from stack, it can be made a static member function:

class stack {
        static int stack_count; // Number of stacks currently in use
        // ... member variables
    public:
        // Right
        static int get_count(  ) {
            return (stack_count);
        }        
        // ... other member functions
};

You can now access the static member function get_count much like you access the static member variable stack_count:

std::cout << "The number of active stacks is " << 
              stack::get_count(  ) << '\n';

Static member functions are very limited. They can't access nonstatic member variables or functions in the class. They can access static member data, static member functions, and functions and data outside the class.