ADTs and C Classes

1
ADTs and C Classes

• Classes and Members
• Constructors
• The header file and the implementation file
• Classes and Parameters
• Operator Overloading

2
Classes and Members

• In C the mechanism to create objects is called
  the class
• Member Functions are the way we manipulate
  objects
• Classes can support information hiding
• Programs use classes without knowing how they are
  implemented

3
Class Members

• C classes have Member Functions and Member
  variables
• Classes can have a public section and a private
  section
• Members in the public session can be seen from
  outside the class
• Members in the private session can not be seen
  from outside the class

4
C class syntax (definition)

• The class head
• The member list
• The public section
• Member functions (Typically)
• Member variables (Occasionally)
• The private section
• Member variables (Typically)
• Member functions (Occasionally)

5
A common pattern for new classes

• Public member functions permit programmers to
  modify and examine objects of the new class
• Constant public members let a member function
  examine data (but not modify it)
• Private member variables store information about
  the status of an object of the new class (not
  available outside the class itself)

6
Using a Class

• To use a class, we create an instance of the
  object
• Each instance has its own private data and its
  own member functions
• We activate the member functions to tell the
  object to perform the behavior This is sometimes
  referred to as sending a message to the object

7
Implementing a Member Function

• Member functions are attached to their respective
  classes with the
• scope resolution operator ()
• The operator is placed between the class name and
  the function name
• A function definition looks like this
• ltreturn typegt ltclass namegtltfunction name()gt
• void myclassmyFunction()

8
The Key to Member Variables

• Each object keeps its own copies of all member
  variables
• When a member functions implementation refers to
  a member variable, then the actual member
  variable always comes from the object that
  activated the member function

9
Constructors

• Provides an initialization function that is
  guaranteed to be called.
• It is called every time an instance of the class
  is created.
• It can have several different number of and type
  of parameters.
• Since it operates inside a class, it does not
  have any return value (no return type allowed)

10
Constructor (cont)

• A constructor with no parameters is called the
  default constructor
• When a class has no constructor, the compiler
  automatically creates the automatic default
  constructor that simply calls the default
  constructor for member variables that are objects
  of other classes
• You should never depend on the automatic default
  constructor

11
Parameters

• Value parameters
• Reference parameters
• Constant reference parameters

12
Inline Member Functions

• Placing a function definition inside a class
  definition is a called an inline member function
• You dont have to write the implementation later
• Inline functions can cause some inefficiency,
  result in messier class definitions and should
  only be used when the function consists of a
  single short statement

13
Header and Implementation Files

• A header file provides all the information that a
  programmer needs in order to use the class
• An implementation file that provides the actual
  implementations of the classs member functions

14
Compiler Directive

• A compiler directive in the header file, called a
  macro guard prevents duplicate class definitions
• ifndef ltclass identifiergt or (!defined)
• define ltclass identifiergt
• ltclass definitiongt
• endif

15
Value Semantics of a Class

• The assignment operator copies the values for
  each member variable. Called the automatic
  assignment operator. Do not work under certain
  situations (discussed later on )
• A copy constructor is a constructor with exactly
  one argument that is the same type as the
  constructors class that creates a new object by
  coping an object of the same type default is
  automatic copy constructor

16
The Constant Declaration

• A (usually) global definition of a constant that
  can not change while the program is running
• A more meaningful way to express a value used
  throughout a program
• Localizes the change of the constant to a single
  point in the program

17
Classes and Parameters

• When functions communicate, they do so by using
  parameters. Understanding the use of parameters
  is essential for writing correct programs.
• Default arguments can be listed in the function
  prototypes of any function.
• A default constructor may be implemented with
  default arguments for all of its arguments.

18
Parameters

• The function parameter is referred to as the
  formal parameter.
• The passed value is the argument, also called the
  actual parameter or the actual argument.

19
Value Parameters

• A value parameter is declared by writing the type
  name followed by the parameter name. A local copy
  is made for use by the function. Data passed into
  a value returning function are always value
  parameters. Some values passed into a void
  function may be value parameters

20
Reference Parameters

• A reference parameter is declared by writing the
  type name followed by the character and the
  parameter name. Changes made to the formal
  parameter will change value of the actual
  parameter in the calling function. Use to pass
  data out of a function. data may originate in
  the function or be changed from data passed into
  the function

21
Constant Reference Parameters

• A constant reference parameter is a reference
  parameters declared with the keyword const before
  the reference parameter. The compiler will not
  allow code to be written that would attempt to
  alter the value of the argument.

22
Operator Overloading

• C lets you define the meaning of many operators
  for a new class
• This new definition is called overloading the
  operator
• The overloaded function has the name operator
  ltoperator symbolgt
• e.g. operator overloads the equivalence
  operator

23
Overloading Input and Output Operators

• The return type is called a reference return type
  which permits chaining of output statements
• The function returns the same stream it has just
  written (read)

24
Friend Functions

• A friend function is a function that is not a
  member function, but still has access to the
  private member variables
• The functions prototype is proceeded by the
  keyword friend
• Friendships should be limited to functions that
  are written by the programmer who implemented the
  class

25
Summary

• Object-oriented programming supports information
  hiding by placing data in packages called
  objects.
• Objects are manipulated by member functions
  defined along with their classes.

26
Summary

• Abstract Data Types (ADTs) are programmer defined
  data types. The term abstract emphasizes that the
  behavior of the ADT is what the user is concerned
  with.
• We create objects that exhibit the behavior of
  the problem we are trying to solve.