Operator Overloading

1. Operator Overloading • Operator Overloading allows a programmer to define new types from the built-in types. • Operator Overloading is useful for redefining built-in operations for user defined types. • Operator Overloading should be used to perform the same function or similar function on class objects as the built-in behavior.

2. Operator Overloading • An operator is overloaded by writing a function definition that has a function name of operator followed by the symbol for the operator to be overloaded. operator- will define a function that overrides the built-in subtraction operator.

3. Operator Overloading • There are two operators that will work with user defined objects. • The assignment operator (=) • The assignment operator will do a member wise assignment of the data members of the class. • The address operator (&) • The address operator simply returns the address of the object in memory.

4. Operator Overloading • Page 526 lists all the operators that may be overloaded as well as the operators that can not be overloaded. • There are 5 operators that can not be overloaded. . .* :: ?: sizeof

5. Operator Overloading • Overloading an operator does notchange: • the operator precedence, • the associativity of the operator, • the arity of the operator, or • the meaning of how the operator works on objects of built-in types.

6. Operator Overloading • Each individual operator must be overloaded for use with user defined types. • Overloading the assignment operator and the subtraction operator does not overload the -= operator.

7. Operator Functions • Operator functions may be defined as either member functions or as non-member functions. • Non-member functions are usually made friends for performance reasons. • Member functions usually use the this pointer implicitly.

8. Operator Functions • The operator overloading functions for overloading (), [], -> or the assignment operators must be declared as a class member. • All other operators may be declared as non-member functions.

9. Member Functions • When an operator function is implemented as a member function: • The leftmost operator must be a class object or reference to a class object of the operator’s class. • If the function must access private or protected data, then the function must be defined as a friend function.

10. Non-member Functions • When an operator function is implemented as a non-member function: • The left-most operand may be an object of the operator’s class, an object of a different class, or a built-in type.

11. Non-member Functions • Non-member functions are not required to be defined as friends if the class contains the appropriate set and get methods are defined as public.

12. Complex Numbers • Complex numbers consist of two pairs the real and the imaginary parts. realPart + imaginaryPart * i where i has a value • A program should be able to input and output complex numbers. • A program should be able to add, subtract, and multiply complex numbers. • A program should also be able to compare complex numbers.

13. Overloading Unary Operators • Unary operators can be overloaded as: • non-static member functions with no arguments,or as • non-member functions with one argument where the argument must be either an object of the class or a reference to an object of the class.

14. Overloading Unary Operators • The preference for overloading unary operators is to make the operator functions class members instead of non-member friend functions.

15. Overloading Binary Operators • Binary operators can be overloaded as: • non-static member functions with one argument, or as • a non-member function with two arguments where one of the arguments must be either a class object or a reference to a class object.

16. Type Conversions • Compilers do not know how to convert between user defined types and built-in types. • Such conversions must be defined by the programmer using conversion constructors

17. Type Conversions • A conversion constructor (cast operator) is a single argument constructor that converts the objects of other types or built-in types into objects of a particular class. • Overloading the cast operator must be a non-static member function, they can not be defined as friend functions.

18. Type Conversion • Overloaded casting operators do not have a return type.

19. Overloading ++ and -- • When ++ and/or -- are overloaded, both pre-increment/decrement and post-increment/decrement must be overloaded. • Each version must have a distinct signature.

20. Overloading ++ and -- • It is standard practice to implement the pre-increment/decrement member function without out parameters. • Date &operator++(); • It is C++ standard to implement the post-increment/decrement member function with a dummy parameter of type int. • Date operator++(int ); • d1.operator++(0); // where the zero is used to indicate the signature for the post increment.

21. Overloading ++ and -- • Date implementation for ++ and --.