1. C++ OOP :: Operator Overloading 06/10/2009 1 Hadziq Fabroyir - Informatics ITS

2. Function Signatures A function signature is what the compiler and linker use to identify a function. In C , functions are identified only by their name In C++ , a function’s signature includes its name, parameters, and (for member functions) const. It does NOT include the return type. 06/10/2009 Hadziq Fabroyir - Informatics ITS 2

3. Ex: C++ swap( ) Function We still need separate functions, but they can all have the same name. For Examples: void swap (int& a, int& b); void swap (double& a, double& b); void swap (struct bob& a, struct bob& b); 06/10/2009 Hadziq Fabroyir - Informatics ITS 3

4. Operator Overloading Overview Many C++ operator are already overloaded for primitive types. Examples: + - * / << >> It is often convenient for our classes to imitate the operations available on primitive types (e.g., + or - ). Then we can use the same concise notation for manipulating our objects. 06/10/2009 Hadziq Fabroyir - Informatics ITS 4

5. Ex: Complex Number Class class Complex {public: Complex (int real = 0, int imagine = 0); int getReal ( ) const; int getImagine ( ) const; void setReal (int n); void setImagine (int d); private: int real; int imagine; }; 06/10/2009 Hadziq Fabroyir - Informatics ITS 5

6. Using Complex Class It makes sense to want to perform mathematical operations with Complex objects. Complex C1 (3, 5), C2 (5, 9), C3; C3 = C1 + C2; // addition C2 = C3 * C1; // subtraction C1 = -C2; // negation 06/10/2009 Hadziq Fabroyir - Informatics ITS 6

7. Operators Are Really Functions For user-defined types, when you use an operator, you are making a function call. Consider the expression: C2 + C1 This is translated into a function call. The name of the function is “operator+” The call is: C2.operator+(C1); 06/10/2009 Hadziq Fabroyir - Informatics ITS 7

8. Declaring operator+As a Member Function class Complex { public: const Complex operator+ (const Complex &operand) const; … }; Note all of the const’s! 06/10/2009 Hadziq Fabroyir - Informatics ITS 8

9. operator+ Implementation const Complex Complex :: operator+ (const Complex &operand) const { Complex sum; // accessor and mutators not required sum.imagine = imagine + operand.imagine; // but preferred sum.setReal( getReal( ) + operand.getReal ( ) ); return sum; } 06/10/2009 Hadziq Fabroyir - Informatics ITS 9

10. Using operator+ We can now write C3 = C2 + C1; We can also use cascading operators. C4 = C3 + C2 + C1; And we can write C3 = C2 + 7; But C3 = 7 + C2 is a compiler error. (Why?) 06/10/2009 Hadziq Fabroyir - Informatics ITS 10

11. operator+ As aNon-member, Non-friend const Complex operator+ (const Complex &lhs, // extra parameter const Complex &rhs) // not const { // must use accessors and mutators Complex sum; sum.setImagine (lhs.getImagine( ) + rhs.getImagine( ) ); sum.setReal (lhs.getReal ( ) + rhs.getReal( ) ); return sum; } // is now commutative 06/10/2009 Hadziq Fabroyir - Informatics ITS 11

12. Printing Objects Each object should be responsible for printing itself. This guarantees objects are always printed the same way. It allows us to write intuitive output code: Complex C5 (5, 3);cout << C5 << endl; 06/10/2009 Hadziq Fabroyir - Informatics ITS 12

13. Operator<< The insertion operator << is a function and can (and should) be overloaded. We can do operator>>, too. << is a binary operator. The left-hand operand is of type ostream& Therefore, operator<< cannot be a member function. It must be a non-member. 06/10/2009 Hadziq Fabroyir - Informatics ITS 13

14. operator<< ostream& operator<< (ostream& out, const Complex& c) { out << c.getReal( ); int imagine = c.getImagine( ); out << (imagine < 0 ? “ - ” : “ + ” ) out << imagine << “i”; return out; } 06/10/2009 Hadziq Fabroyir - Informatics ITS 14

15. Operator<<Returns Type ‘ostream &’ Why? So we can write statements such as cout << C5 << “is a complex number” OR cout << C3 << endl << C2 << endl; << associates from left to right. 06/10/2009 Hadziq Fabroyir - Informatics ITS 15

16. Overloading Unary Operators Complex C1(4, 5), C2; C2 = -C1; is an example of a unary operator (minus). We can and should overload this operator as a member function. 06/10/2009 Hadziq Fabroyir - Informatics ITS 16

17. Unary operator- const Complex Complex :: operator- ( ) const { Complex x; x.real = -real; x.imagine = imagine; return x; } 06/10/2009 Hadziq Fabroyir - Informatics ITS 17

18. Overloading = Remember that assignment performs a memberwise (shallow) copy by default. This is not sufficient when a data member is dynamically allocated. =must be overloaded to do a deep copy. 06/10/2009 Hadziq Fabroyir - Informatics ITS 18

19. Restrictions Most of operators can be overloaded. You can’t make up your own operators. You can’t overload operators for primitive types (like int). You can’t change the precedence of an operator. You can’t change the associativity of an operator. 06/10/2009 Hadziq Fabroyir - Informatics ITS 19

20. Converting between Types Cast operator Convert objects into built-in types or other objects Conversion operator must be a non-static member function. Cannot be a friend function Do not specify return type For user-defined class A A::operator char *() const; // A to char A::operator int() const; //A to int A::operator otherClass() const; //A to otherClass When compiler sees (char *) s it calls s.operator char*() 06/10/2009 Hadziq Fabroyir - Informatics ITS 20

21. Good Programming Practices Overload operators so that they mimic the behavior of primitive data types. Overloaded binary arithmetic operators should return const objects by value be written as non-member functions when appropriate to allow commutativity be written as non-friend functions (if data member accessors are available) Overload unary operators as member functions. Always overload << Always overload = for objects with dynamic data members. 06/10/2009 Hadziq Fabroyir - Informatics ITS 21

22. Another Example Vectors in the Plane Suppose we want to implement vectors in 2D and the operations involving them. 06/10/2009 Hadziq Fabroyir - Informatics ITS 22

23. For your practice … Exercise Vector2D Class Properties: double X, double Y Method (Mutators): (try) all possible operators that can be applied on Vector 2D (define methods of) the remains operation that can’t be overloaded Lab Session for lower order (Senin, 15.00-17.00) Lab Session for upper order (Senin, 19.00-21.00) Please provide: the softcopy(send it by email – deadline Sunday 23:59) the hardcopy(bring it when attending the lab session) 06/10/2009 Hadziq Fabroyir - Informatics ITS 23

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