Operator Overloading Friend Functions

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Operator Overloading Friend Functions
Special Forms
Department of Computer and Information
Science,School of Science, IUPUI
Dale Roberts, Lecturer Computer Science,
IUPUI E-mail droberts_at_cs.iupui.edu
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Operator Overloading Using a Friend Function

• Number of Parameters Accepted by an Overloaded
  Friend Operator Function Depend Upon the Operator
  Type -- One for Unary Operators and Two for
  Binary Operators
• class complex
• int re, im
• public
• complex(int ip1 0, int ip2 0)
• re(ip1), im(ip2)
• friend complex operator(complex,
  complex)
• //Friend Operator Function
• complex operator(complex a, complex b)
• return complex(a.reb.re, a.imb.im)
• main()
• complex one(1,1), two(2,2), three
• three one two //three
  operator(one, two)

Is a friend function necessary in this case? No
because LH operand is an instance of the class.
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Operator Functions as Class Members vs. as friend
Functions

• Non-member overloaded operator functions
• Enable the operator to be commutative
• HugeInteger bigInteger
• int integer
• bigInteger integer bigInteger
• or
• bigInteger bigInteger integer

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Global Operator Overloading

• Similar to friend Function Overloading, Except
  the Keyword friend is Omitted and Global
  Functions CANNOT ACCESS private Members
• class complex //All Public Members!
• public
• int re, im
• complex(int ip1 0, int ip2 0)
• re(ip1), im(ip2)
• void operator!(complex a)
• int temp a.re a.re a.im a.im temp
• cout ltlt "Real " ltlt a.re ltlt endl
• cout ltlt "Imaginary " ltlt a.im ltlt endl
• main()
• complex one(1,2)
• !one

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Overloading of Operators Having a Variable Arity

• Operators Such as - Can be Unary or Binary
• Overloading of Such Operators Involves Creating a
  Unary Function (One Operand) and a Binary
  Function (Two Operands)
• Only if Both the Forms are Used, They Need to be
  Implemented
• class number
• int n
• public
• number(int x 0)n(x)
• number operator-()n -n return this
• number operator-(number ip)
• n n ip.n return this
• main()
• number one(1), two(2), three
• one -one //unary operator
• three one - two //three.n -3

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Operators with Prefix and Postfix Forms

• Separate Functions for Each -- Prefix and Postfix
  -- Forms are Needed
• Prefix Form is Treated as an Unary Operator
• Postfix Form is Treated as a Binary Operator

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Prefix Overloaded Function -- Example

• class number
• int n
• public
• number(int x)n(x) //Constructor
• //prefix operator -- unary
• number operator()
• number numberoperator()
• n return this
• main()
• number one(10) //one.n 10
• one //one.n 11

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Postfix Overloaded Function -- Example

• Postfix Operator is Implemented as a Binary
  Operator with an int Argument with a Default
  Value of 0 . When specifying an overloaded
  operator for the postfix form of the increment or
  decrement operator, the additional argument must
  be of type int specifying any other type
  generates an error.
• class number
• int n
• public
• number(int x)n(x) //Constructor
• //postfix operator -- binary -- int
  argument
• number operator(int)
• number numberoperator(int y)
• if (y ! 0) n y else n return
  this

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Postfix overloaded functionExample (Cont)

• main()
• number one(10) // one.n 10
• one // one.n 11
• one.operator(2) // one.n 13
• There is no syntax for using the increment or
  decrement operators to pass these values other
  than explicit invocation, as shown in the
  preceding code. A more straightforward way to
  implement this functionality is to overload the
  addition/assignment operator ().

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Special Overloading Forms

• A Few Operators Require Special Treatments During
  Overloading
• Conversion Operator
• const Array Operator
• Function Call -- Parenthesis Operator
• Stream Insertion -- ltlt Operator
• Stream Extraction -- gtgt Operator
• Pointer to Member -- -gt Operator
• Assignment Operator
• new Operator
• delete Operator

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Overloading Stream-Insertion and
Stream-Extraction Operators

• Overloaded ltlt and gtgt operators
• Must have left operand of types ostream ,
  istream respectively
• It must be a non-member function (left operand
  not an object of the class)
• It must be a friend function if it accesses
  private data members

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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
• Aoperator char () const // A to char
• Aoperator int() const //A to int
• Aoperator otherClass() const //A to
  otherClass
• When compiler sees (char ) s it calls
• s.operator char()

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Converting between Types (cont)

• The compiler can call these functions to create
  temporary objects.
• If s is not of type char
• Calls Aoperator char () const for
• cout ltlt s

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Special overloading forms - Example

• Special Forms Example

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Acknowledgements

• These slides were originally development by Dr.
  Uday Murthy and Dr. Rajeev Raje.
• Some contents comes from the Deitel slides that
  accompany your text.
• Some information regarding the postfix form the
  increment and decrement operators comes from MSDN.