Question

UPDATE::

OK so I have these new lines in the header file:

static void gcdStatsCounter();//increments counter
static void display(); // displays the gcdStats
static int gcdStats;//• calls to gcd

public:                                  // interface routines
        static void statistics();              // print statistics

Then I added into the cpp file:

int Rationalnumber::gcdStats(0);//initialization

void Rationalnumber::gcdStatsCounter() { // counter incrementer
    gcdStats++;
}

void Rationalnumber::display() {// displays the gcdStats
    cout << "gcdStats = " << Rationalnumber::gcdStats << endl;
}

void statistics() {
    Rationalnumber::display();
}                       // print statistics

It is giving me the error: static void Rationalnumber::display() is private. The challenge is for me to only add private members and not touch the interface routines 🙁 Friend functions are to be avoided. Any ideas?

ORIGINAL POST::

I am having trouble updating static counter variables under the section: // MY MEMBERS

The rules: “Do not change, add or remove members of the GIVEN code for the interface. You may add private members if needed, but no other changes are allowed.”

My problem is how can I update private members without creating new public functions? I understand that I need a static private member function to access a static private member variable. However, whenever I try to access the static private counter variable, I get an error “undefined reference to…” For example, this private counter function (declared as static) for gcdStats will give me such an error:

void Rationalnumber::gcdStatsCounter() {
    gcdStats++;
}

The header file:

#ifndef RATIONALNUMBER_H
#define RATIONALNUMBER_H
#include <iostream>
// HEADER FILE

class Rationalnumber
{
    friend bool operator==( Rationalnumber l, Rationalnumber r );
    friend bool operator!=( Rationalnumber l, Rationalnumber r );
    friend bool operator<( Rationalnumber l, Rationalnumber r );
    friend bool operator<=( Rationalnumber l, Rationalnumber r );
    friend bool operator>( Rationalnumber l, Rationalnumber r );
    friend bool operator>=( Rationalnumber l, Rationalnumber r );

    friend Rationalnumber operator+( Rationalnumber l, Rationalnumber r );
    friend Rationalnumber operator-( Rationalnumber l, Rationalnumber r );
    friend Rationalnumber operator*( Rationalnumber l, Rationalnumber r );
    friend Rationalnumber operator/( Rationalnumber l, Rationalnumber r );

    friend std::istream &operator>>( std::istream &is, Rationalnumber &r );
    friend std::ostream &operator<<( std::ostream &os, Rationalnumber r );

    int num, denom;                        // implementation


    // MY MEMBERS

    // functions
    static int gcd(int n, int d); // for the gcd function
    static void zeroDenom(); // is called whenever denom = 0

    // variables
    // object stats:
    // The first four statistics vary depending on the implementation approach
    static void gcdStatsCounter();
    static int gcdStats;//• calls to gcd
    static int con;     //• rational-number objects created by regular constructors
    static int copy;    //• rational-number objects created by copy constructor
    static int des;     //• rational-number objects destroyed by destructor

    //operation stats:
    // must be consistent across implementations
    static int assn;    //• assignments to rational-number objects
    static int rel;     //• relational/equality operations between rational-number objects
    static int add;     //• addition/subtraction operations between rational-number objects
    static int sub;
    static int mul;     //• multiplication/division operations between rational-number objects
    static int div;
    static int in;      //• input/output operations on rational-number objects
    static int out;


  public:                                  // interface routines
    Rationalnumber();
    Rationalnumber( int n );
    Rationalnumber( int n, int d );
    Rationalnumber( const Rationalnumber &c ); // copy constructor
    ~Rationalnumber();

    int numerator() const;                 // return numerator
    int numerator( int n );                // set numerator to n; return previous numerator
    int denominator() const;               // return denominator
    int denominator( int d );              // set denominator to d; return previous denominator

    Rationalnumber operator-();            // unary negation
    Rationalnumber &operator=( const Rationalnumber &r ); // assignment

    static void statistics();              // print statistics

}; // Rationalnumber

#endif // __RATIONALNUMBER_H__

UPDATE::SEE TOP

Answer 1

You’ve only declared your static members, you have not defined them.

Generally with static variables, you need to declare them inside the class definition and then define them outside, for example:

class Rationalnumber
{

    static float f;
    //...

};

Edit: Of course, the definition should go in the .cpp file, not in your header file. The reason for this is to avoid multiple definitions, which can happen if your header file is included in more than one source file. The linker is tasked with initializing static objects, and the lines below basically tell the linker that it exists and what to do with it.

//In Rationalnumber.cpp:
float Rationalnumber::f; //Allow default initialization
float Rationalnumber::f(5.0); //Initialize with non-default value