The following code example is taken from the book
Object-Oriented Programming in C++
by Nicolai M. Josuttis, Wiley, 2002
© Copyright Nicolai M. Josuttis 2002
#ifndef FRACTION_HPP
#define FRACTION_HPP
// include standard header files
#include <iostream>
// **** BEGIN namespace CPPBook ********************************
namespace CPPBook {
class Fraction {
protected:
int numer;
int denom;
public:
/* error class
*/
class DenomIsZero {
};
/* default constructor, one-, and two-parameter constructor
*/
Fraction(int = 0, int = 1);
/* multiplication
* - global friend function, so that an automatic
* type conversion of the first operand is possible
*/
friend Fraction operator * (const Fraction&, const Fraction&);
/* multiplicative assignment
* - new: virtual
*/
virtual const Fraction& operator *= (const Fraction&);
/* comparison
* - global friend function, so that an automatic
* type conversion of the first operand is possible
*/
friend bool operator < (const Fraction&, const Fraction&);
/* output to and input from a stream
* - new: virtual
*/
virtual void printOn(std::ostream&) const;
virtual void scanFrom(std::istream&);
/* type conversion to double
* - new: virtual
*/
virtual double toDouble() const;
// new: virtual destructor (without instructions)
virtual ~Fraction() {
}
};
/* operator *
* - global friend function
* - inline defined
*/
inline Fraction operator * (const Fraction& a, const Fraction& b)
{
/* simply multiply numerator and denominator
* - this saves time
*/
return Fraction(a.numer * b.numer, a.denom * b.denom);
}
/* standard output operator
* - overloaded globally and inline defined
*/
inline
std::ostream& operator << (std::ostream& strm, const Fraction& f)
{
f.printOn(strm); // call member function for output
return strm; // return stream for chaining
}
/* standard input operator
* - overloaded globally and inline defined
*/
inline
std::istream& operator >> (std::istream& strm, Fraction& f)
{
f.scanFrom(strm); // call member function for input
return strm; // return stream for chaining
}
} // **** END namespace CPPBook ********************************
#endif // FRACTION_HPP