![Operators That Can Be
Overloaded
+ - * / % ^ & |
~ ! = < > += -= *=
/= %= ^= &= |= << >> >>=
<<= == != <= >= && || ++
-- ->* ‘ -> [] () new delete
new [ ] delete [ ]](https://image.slidesharecdn.com/overloading-121209032109-phpapp02/85/Overloading-6-320.jpg)
![Using member functions
• If the first operand of the operator is a class
instance or a reference to a class instance, the
overloaded operator can be implemented as a
member function.
• Example invocation
object = object1 + object2;
• Translated by compiler to
object = object1.operator+(object2);
• When overloading (), [], -> or any of the
assignment operators, the operator overloading
function must be declared as a class member.](https://image.slidesharecdn.com/overloading-121209032109-phpapp02/85/Overloading-9-320.jpg)
Overloading
- 1. Operator Overloading Reading: Chapter 8
- 2. Why overload operators? • We can define new data types using classes. • Member functions are invoked by sending messages. • For many classes, this notation is cumbersome. • For some classes, especially mathematical ones, it would be nice to be able to use operators with instances of these classes.
- 3. Example • Suppose we have: – a class (called Time) for representing time of the day – two Time objects time1 and time2 • We want to be able to do things like – compare times if (time1 < time2) – print times to an output stream cout << "The first time is " << time1 << endl;
- 4. Simple example in C++ • The division operator / is used for – integer division – floating point division • Actually performs two different types of division, but we use the same operator, i.e., it is overloaded. • We will talk about how to overload or redefine our own operators for classes …
- 5. How to overload operators? • An overloaded operator is nothing but a – function • The name of the function is the keyword operator followed by the symbol for the operator being overloaded. • Example: – the function name operator+ would be used to overload the + operator.
- 6. Operators That Can Be Overloaded + - * / % ^ & | ~ ! = < > += -= *= /= %= ^= &= |= << >> >>= <<= == != <= >= && || ++ -- ->* ‘ -> [] () new delete new [ ] delete [ ]
- 7. Details • Overloading an operator like + allows statements like: object1 + object2 • This does not allow statements like: object1 += object2 • The += operator must be overloaded separately. • The "aritiy" (number of operands) of the operator cannot change.
- 8. Implementing operator overloading • The functions must have access to the private member data of the class. • Two ways to write operator overloading functions: – Member functions – Friend functions
- 9. Using member functions • If the first operand of the operator is a class instance or a reference to a class instance, the overloaded operator can be implemented as a member function. • Example invocation object = object1 + object2; • Translated by compiler to object = object1.operator+(object2); • When overloading (), [], -> or any of the assignment operators, the operator overloading function must be declared as a class member.
- 10. Example - Rational Numbers class Rational { public: Rational(int n = 0, int d = 1); Rational operator+(const Rational &a) const; Rational operator-(const Rational &a) const; Rational operator*(const Rational &a) const; private: int numerator; int denominator; }
- 11. Overloaded multiplication Rational Rational::operator*(const Rational & a) { int n = (*this).numerator * a.numerator; int d = (*this).denominator * a.denominator; return Rational(n,d); }
- 12. Assignment • Write the 2 other overloaded operators for the Rational class.
- 13. Rational Rational::operator+(const Rational & a) { int commonD = denominator * a.denominator; int n = denominator * a. numerator + numerator * a. denominator; return Rational(n,commonD); }
- 14. Using friend functions • If the first operand of a binary operator is not a class instance nor a reference to a class instance, the overloaded operator can be implemented as a friend function • Both operands are function arguments. • Example invocation cout << object1; • Translated by compiler to operator<<(cout,object1);
- 15. Example: Overloading << and >> • We often want to overload the insertion (>>) and extraction (<<) operators so that objects can be written and read using these operators. • Phone number example: want to be able to read and write in format like (662) 325-7505 • Input statements might look like cin >> phone1; • Output statements might look like cout << "My phone number is " << phone1 << endl;
- 16. Overloading << and >> class PhoneNum { friend ostream& operator<< (ostream&, const PhoneNum&); friend istream& operator>> (istream&, PhoneNum&); private: int areaCode; int prefix; int number; };
- 17. Overloading << and >> ostream& operator<< (ostream &output, const PhoneNum &num) { output << "(" << num.areaCode << ") " << num.prefix << "-" << num.number; return output; }; istream& operator>> (istream &input, PhoneNum &num) { input >> num.areaCode >> num.prefix >> num.number; return input; };
- 18. Overloading << and >> void main { PhoneNum phone; cout << "Enter phone number like 999 325 0007" << endl; cin >> phone; cout << "The number is:" << phone << endl; };
- 19. Assignment • Rewrite the Time class to include overloaded operators for insertion, extraction, and comparison (>>, <<, and ==) class Time { public: Time( ); void SetTime( int, int, int); void PrintMilitary( ); void printStandard( ); private: int hour; // 0-23 int minute; // 0-59 int second; // 0-59 };