Operator Overloading

• Overloading : giving a single name two functions
  • In our example, print is an overloaded function
  • Look at the print function in rat_test.C
  • Look at the print function in rat.C
  • How does the compiler know which to call?
• A nice thing about C++ is that we can overload all functions
  • This allows us to overload standard operators
  • like + and ++ and = and ==
• Overloading + in the rat class
  • The prototype (in rat.h)
  • rational operator+(rational b);
  • This says, we expect a single rational value b passed in.
  • and it returns a rational
    • w = x + y
    • w = x.add(y)
• The implementation

  
  rational rational::operator+( rational b) {
       rational rv;
       rv.numer = numer* b.denom + b.numer * denom;
       rv.denom = denom * b.denom;
  
       return(rv);
  }
  

• We might want to overload the << operator too.
  • This is more compilcated.
  • What we need to do is add a new function to the outstream class
  • To do this we need to declare what is called a friend function
    • This gives one class access to another classes private parts
  • the prototype:
    • friend ostream& operator <<(ostream & s , rational a);
  • The implementation:

    ostream& operator <<(ostream & s, rational a) {
         s << a.numerator();
         s << "/";
         s << a.denominator();
    
         return(s);
    }