C Lecture 4

1
C Lecture 4

• Function/operator overloading
• Friend functions C example
• UML
• UML diagrams
• Use-case diagram
• Class diagram
• sequence diagram
• Unit Assessment

2
Function/operator overloading

• Function overloading constructor functions
• actual function called determined by the number
  and type of the arguments
• Operators
• Unary e.g. -, !, , , --
• Binary e.g. ,-,,/,ltlt,gtgt etc.
• Operators are treated as functions by C
• Therefore the operators can be overloaded

3
Operator overloading

• It is therefore possible to write operator
  functions for the operators.
• The functions will be called operator_at_, where _at_
  is the actual operator
• There will possibly be many operator functions
  all with the same name. They must differ in the
  number and type of their arguments.
• This is operator overloading.

4
Operators as functions

• Consider an object obj of class CAny
• CAny obj
• The normal way of invoking a member function of
  the class CAny is -
• obj.func()
• Now consider a binary operator e.g. objx _at_
  objy
• where objx and objy are instances of some
  class and _at_ is a binary operator such as ,-,,/,
  ltlt or gtgt

5
Operators as functions

• objx _at_ objy is interpreted by the C compiler in
  on of two ways
• objx.operator_at_(objy)
• i.e. the compiler looks for a a member function
  called operator_at_ in the class of which objx is an
  instance.
• if such a member function cannot be found in the
  class then the following is tried
• operator_at_(objx, objy)
• i.e. the compiler looks for an ordinary function
  called operator_at_ that takes two arguments with
  the appropriate data types.

6
Operator overloading

• We have a choice over which method to implement
• either as a member function of a class
• or as an ordinary function
• objx _at_ objy is treated as objx.operator(objy)
• If the operator is a member function then this
  implies that the object to the left of the
  operator MUST be an instance of the class
  containing the operator function.
• What if the object on the left is not an instance
  of the class containing the operator function?

7
Friend Functions

• We might therefore implement the operator as an
  ordinary function-
• operator_at_(objx, objy)
• Since this is NOT a member function how can it
  access the private data of the objects
• the objx, objy class could have appropriate
  accessor and mutator functions. This would be
  less efficient than if the operator function
  could access the private data directly.
• C added Friends!

8
Friend Functions

• Friends are functions or whole classes which are
  granted access to the private data of a
  class.This breaks the encapsulation
• A friend is declared within the class which is
  allowing friendship.
• A function cannot make itself a friend of a
  class.
• Friendship should be used thoughtfully and
  sparingly
• A common use of friend functions is to allow the
  use of ltlt and gtgt with cout and cin for output and
  input of user defined types.

9
Unified Modelling Language - UML

• UML is a modelling tool to capture and represent
  in the form of diagrams and text the various
  stages of the software development process
• There are 8 different diagram types. We shall
  only consider 3
• Use-case capture user interaction with the
  system
• Class show relationship between objects and
  classes
• Sequence show the interaction of objects.
• Rational Rose UML development tool

10
(No Transcript)