Function Overloading

1
Function Overloading

• Can enables several function
• Of same name
• Of different sets of parameters (at least as far
  as their types are concerned)
• Used to create several functions of the same name
  that perform similar tasks but on different data
  types

2
Square function

• int square(int x)
• return xx
• double square(double y)
• return yy
• float square(float z)
• return zz

3
Use overloaded function

• Complier will search for the match function
  prototype
• int main()
• int x7
• double y7.5
• coutltltsquare of ltltxltlt is
• ltltsquare(x)ltltendl
• coutltltSquare of ltltyltltis
• ltltsquare(y)ltltendl

4
Friend function and friend class

• A friend function of a class is defined outside
  that class scope
• Has right to access private members of the class
• Using friend functions can enhance performance
• Often appropriate when a member function cannot
  be used for certain operations

5
Declare a function as friend

• To declare a function as a friend of a class,
  precede the function prototype in class
  definition with key word friend
• To declare a class Two as a friend of One, place
• friend class Two
• in the definition of class One

6
Friendship

• Friendship is granted, not taken
• Friendship is not symmetric
• If B is friend of A, I.e. A declared B as friend,
  you cannot infer A is friend of B unless B
  declare A as friend
• Friendship is not transitive
• A is friend of B, and B is friend of C, you
  cannot say that A is friend of C

7
Example

• class Count
• friend void setX(Count , int)
• public
• Count()x0
• void print() const coutltltxltltendl
• private
• int x

8
Example continue

• void setX(Count c, int val)
• c.x val
• int main()
• Count counter
• counter.print()
• setX(counter, 8)
• return 0

9
Use this pointer

• Every object has access to its own address
  through a pointer called this
• This pointer is not part of object
• This pointer is passed into object (by compiler)
  as implicit first argument on every non-static
  member function

10

• class Test
• int x
• public
• Test( int 0)
• void print() const
• Testtest(int a) x a
• void Testprint() const
• coutltlt x ltltx
• ltlt\nthis-gtx ltltthis-gtx
• ltlt\n(this).x ltlt(this).x ltltendl

11

• int main()
• Test t(12)
• t.print()
• return 0

Output
x 12 this-gtx 12 (this).x 12
12
Operator Overloading

• Enable Cs operators to work with class object
• ltlt, gtgt, , -, , /
• This operators perform differently depending on
  their context in integer, floating
• These operators are overloaded
• C allow programmer to overload most operators

13
Can we make Complex class easier to use as follow?

• int main()
• Complex x,y,z
• coutltltType in two complex numbers\n
• cingtgtx gtgty
• z x y
• coutltlt x ltlt ltltyltlt ltltzltltendl

Type in two complex numbers (2,3) (3,4) (2,3)
(3,4) (5,7)
14
Yes, Overload the operators

• Operator are overloaded by writing a function
  definition( header and body)
• Function name become the keyword operator
  followed by the symbol for the operator being
  overloaded
• operator would be used to overload the
  addition operator()
• Precedence and associativity of an operator
  cannot be changed by overloading

15
Where to define overloading operator

• As non member function
• Must be friend of the class
• So it is in class definition
• class Complex
• friend ostream operatorltlt
• (ostream, const Complex )
• ...

Function name
Return type
parameters
16
Implementation

• ostream operatorltlt(ostream out, const
  Complex c)
• outltlt(ltltc.realltlt,ltltc.imgltlt)
• return out
• // enables coutltltxltlty

17
Overload operator gtgt

• In class definition
• class Complex
• friend ostream operatorltlt
• (ostream , const Complex )
• friend istream operatorgtgt
• (istream, Complex )
• ...

18
implementation

• istream operatorgtgt( istream
• input,Complex c)
• input.ignore()
• inputgtgtc.real
• input.ignore()
• inputgtgtc.img
• input.ignore()
• return input