Using Static Member Function to Access Static Data Member

Question

I am trying to access a static data member using a static member function, so that I may call this function and retrieve the data member. The goal is to increase/decrease this static data member to count how many objects are existing in the program.

Verbatim from assignment:

A static member function called getNumObjects should be provided that takes no parameters and returns an int indicating the number of objects of type Complex currently in existence.

My code so far:

Complex.hpp

class Complex{
public:
...
// Get the number of complex objects in the current program
        static int& getNumObjects();
...

private:
...
        static int counter; // static counter
...
}

Complex.cpp

// Initialize object counter for getNumObjects()
int Complex::counter = 0;
// Get number of objects existing in the current program
static int& Complex::getNumObjects(){
        return counter;
}

testComplex.cpp

// checks to see how many complex objects are open currently
        std::cout << "How many complex objecst are in existence? ";
        int num = Complex::getNumObjects();
        std::cout << num << '\n';
        std::cout << "successful\n";

I don't understand why the compiler keeps throwing me this error:

 error: cannot declare member function ‘static int& Complex::getNumObjects()’ to have static linkage [-fpermissive]
 static int& Complex::getNumObjects(){

or this error:

In function ‘int getNumObjects()’:
/../../../ error: ‘counter’ was not declared in this scope
  return counter;
         ^~~~~~~
/../../../ note: suggested alternative: ‘toupper’
  return counter;
         ^~~~~~~
         toupper

I've searched far and wide, I seem to have initialized my private data member just fine as well as the function. getNumObjects() is stated as a class, so why is it saying the scope of the function isn't right?

Answer 1

I don't understand why the compiler keeps throwing me this error:

Because you repeated static in the member function definition. The function is already declared static; C++ syntax requires you to omit static in the cpp file:

int Complex::counter = 0;
// Get number of objects existing in the current program
int& Complex::getNumObjects(){
    return counter;
}

Note: It is probably not a good idea to return int&, because the callers would be able to modify counter without your knowledge:

Complex::getNumObjects() = -123; // <<== returning reference makes this legal

This is very bad, because it completely breaks encapsulation. Essentially, your counter ends up being exposed as if it were a public member variable.

You should change your function to return int instead:

int Complex::getNumObjects(){
    return counter;
}