Multiple File Compilation Problem

[nj1995]

I have this multiple file compilation program and for some reason my overloaded object in my rational.cpp file cant access the private function GCD from the class even though it is a friend of the function. Any help would be greatly appreciated thanks.

//main.cpp:

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include "rational.h"
using namespace std;

int main()
{
	rational r1(1,3), r2(1,3), r3;
	
	cout << "r1 = " << r1;
	cout << endl;
	
	
	cout << "r2 = " << r2;
	cout << endl;
	
	r3 = r1 + r2;
	cout << "r3 = r1 + r2 = " << r3;
	cout << endl;
	
	r3 = r1 - r2;
	cout << "r4 = r1 - r2 = " << r3;
	cout << endl;
	
	r3 = r1 * r2;
	cout << "r5 = r1 * r2 = " << r3;
	cout << endl;
	
	r3 = r1 / r2;
	cout << "r6 = r1 / r2 = " << r3;
	cout << endl;
	
	int com = r1 > r2;
	
	if (com == 1)
		cout << "r1 is greater than r2" << endl;
	else if (com == 0)
		cout << "r1 and r2 are equal" << endl;
	else if (com == -1)
		cout << "r1 is less than r2" << endl;
	
	system ("PAUSE");
	return 0;	
}

//rational.h:

#ifndef RATIONAL_H
#define RATIONAL_H
#include <iostream>
#include <iomanip>
using namespace std;

class rational
{
	friend istream& operator>>(istream&, rational&);
	// User is prompted to enter numerator then denominator for a rational number
	//  Precondition: denominator of rational number must not be zero
	// Postcondition: rational reference object passed to the function is filled with values entered by user

	friend ostream& operator<<(ostream&, rational&);
	// Postcondition: displays the contents of the rational object passed to the function 
	//   Note: the rational number should be displayed in the format of  a / b, e.g., 1 / 2,  -5 /9 (not 5 / -9), 1 / 4 (not 2 / 8), etc.
	//   Moreover, if the rational number is 1 / 1, then display just 1. If the rational number is 0 /5, then display just 0.

public:
	rational();
	// default constructor
	// Postcondition: declared rational object is initialized to 1 (i.e., 1 / 1)

	rational(int aa, int bb);
	// second constructor
	// Postcondition: numerator & denominator of the declared rational object is initialized to aa and bb, respectively and bb ? 0

	void set(int aa, int bb);
	// Postcondition: calling rational object is set to aa / bb

	rational operator+(const rational &r2) const;
	// Postcondition: sum of calling rational object and r2 is returned (notice the return type is rational!)

	rational operator-(const rational &r2) const;
	// Postcondition: (calling rational object – r2) is returned 

	rational operator*(const rational &r2) const;
	// Postcondition: product of calling rational object and r2 is returned 

	rational operator/(const rational &r2) const;
	// Postcondition: (calling rational object / r2) is returned

	int operator>(const rational&r2) const;
	// Postcondition: returns 1 if calling object is greater than r2; 0 if r1 is equal to r2; -1 is r1 is less than r2 

private:
	int GCD() const;
	// You must use the Euclidean algorithm. https://en.wikipedia.org/wiki/Euclidean_algorithm
	// Postcondition: returns the “greatest common divisor” between the numerator and denominator of the calling rational object
	int a;	// numerator
	int b;	// denominator
};

#endif


//rational.cpp:

#include <stdlib.h>
#include "rational.h"
using namespace std;

rational::rational()
{
}

rational::rational(int aa, int bb)
{
	a = aa;
	b = bb;
	
	if (b == 0)
	{
		cout << "Denominator cannot equal 0\n";
		
		exit(1);
	}	
}

void rational::set(int aa, int bb)
{
	cout << "Enter numerator and denominator: \n";
	cin >> aa >> bb;
}

rational rational::operator+(const rational &r2) const
{	
	rational sum;
	sum.a = a * r2.b + r2.a * b;
	sum.b = b * r2.b;
	
	return sum;
}

rational rational::operator-(const rational &r2) const
{
	rational difference;
	difference.a = a * r2.b - r2.a * b;
	difference.b = b * r2.b;
	
	return difference;
}

rational rational::operator*(const rational &r2) const
{
	rational product;
	product.a = a * r2.a;
	product.b = b * r2.b;
	
	return product;
}

rational rational::operator/(const rational &r2) const
{
	rational quotient;
	quotient.a = a * r2.b;
	quotient.b = b * r2.a;
	
	return quotient;
}

int rational::operator>(const rational&r2) const
{
	double r1total, r2total;
	
	r1total = (double) a/b;
	r2total = (double) r2.a/r2.b;
	
	if (r1total > r2total)
		return 1;
	else if (r1total == r2total)
		return 0;
	else 
		return -1;
}

int rational::GCD() const
{
	int n = abs(a);
	int d = abs(b);
	
	while(d != 0)
	{
		int temp = d;
		d = n % d;
		n = temp;
	}
	
	return n;
}

istream& operator>>(istream &in, rational &r2)
{
	in >> r2.a >> r2.b;
	
	return in;
}

ostream& operator<<(ostream &out, rational &r2)
{
	int gcd = GCD();
	
	if (r2.b < 0)
	{
		r2.b = -(r2.b);
		r2.a = -(r2.a);
	}
	
	if(r2.a == 0)
	{
		out << 0;
	}
	
	if(r2.a == r2.b)
	{
		out << 1;
	}
	
	out << r2.a/gcd  << "/" << r2.b/gcd;
	
	return out;
}

[ne555]

> I have this multiple file compilation program and for some reason my
> overloaded object in my rational.cpp file cant access the private function
> GCD from the class even though it is a friend of the function.
overloaded operator
the function is a friend of the class

Not a problem with saying what you understood of the error, but always copy it verbatim.

|| foo.cpp: In function ‘std::ostream& operator<<(std::ostream&, rational&)’:
foo.cpp|211 col 16| error: ‘GCD’ was not declared in this scope
||   int gcd = GCD();
||                 ^

you have declared a non-static member function called GCD().
Because it is a member function you need an object to call it int gcd = r2.GCD();