C for Engineers and Scientists Second Edition

1
C for Engineers and ScientistsSecond Edition

• Chapter 10
• Class Functions and Conversions

2
Objectives

• Assignment
• Additional Class Features
• Operator Functions
• Data Type Conversions
• Applications

3
Objectives (continued)

• Class Inheritance
• Polymorphism
• Common Programming Errors

4
Assignment

• Memberwise assignment copying one object to
  another, a member at a time, as if assigning each
  member individually

5
Assignment (continued)

• Operator overloading constructing your own
  operator in a class
• Use the keyword operator in the function
  declaration
• Example assignment operator

6
Assignment (continued)

• To avoid inadvertent alteration to the object of
  the assignment, use a constant reference
  argument
• void Dateoperator(const Date newdate)
• Assignment does not create a new object, but can
  be part of initialization of a new object
• Examples
• Date b a
• Date b(a)

7
Assignment (continued)

• Copy constructor special constructor whose
  argument is a reference to an object of the same
  class it creates a new object that is a copy of
  the object referenced
• Syntax
• ClassName(const ClassName)
• Compiler provides a default copy constructor that
  performs a memberwise copy can encounter
  problems if the class contains pointer data
  members

8
Assignment (continued)
9
Assignment (continued)

• Base/Member Initialization List a list of values
  applied to constructor functions to initialize
  data members
• List must be specified in the classs declaration
  section
• ClassName(argument list) list of data members
  (initializing values)
• This type of constructor is required when there
  is a const class instance variable

10
Additional Class Features

• Class scope data and function members are local
  to the scope of their class
• Static class member a variable that can be
  shared between all instantiations of a class
  acts as a global variable for the class
• Static variables must be declared within the
  classs declaration section

11
Additional Class Features (continued)
12
Additional Class Features (continued)

• Static member function applies to a class as a
  whole, and can only access static data members
  and other static member functions of the class
• Friend function a non-member function that has
  been granted the same access as a classs own
  functions
• Friends list the list of non-member friend
  functions a list of function prototype
  declarations using the keyword friend

13
Additional Class Features (continued)

• Friend functions
• May be declared anywhere within the declaration
  section usually placed after class header by
  convention
• Use the keyword friend only in the class
  declaration, not in the function definition
• Have at least one argument that is a reference to
  a class object of the class granting it friend
  status
• Can only be given friend status by an external
  class they cannot bestow it on themselves

14
Operator Functions

• Most operators can be overloaded for specific
  purposes within a class, with these limitations
• Cannot create new operator symbols
• Cannot modify precedence or associativity
• Cannot redefine operators for built-in data types
• Unary operators cannot be made binary, and vice
  versa
• Operator must either be a class member or use a
  member as an operand

15
Operator Functions (continued)

• Operator functions functions that define
  operations on class objects and use built-in
  operator symbols
• Operator functions are called by using their
  associated symbols or by using their names
• Examples
• ab
• a.operator(b)

16
Operator Functions (continued)
17
Operator Functions (continued)

• Operator function may be a friend function
• Requires an additional class reference
• Example
• friend Date operator(Date, int)
• Operator Function Argument Requirements

18
Operator Functions (continued)
19
Operator Functions (continued)

• Operator Function Guidelines
• Friend functions are more appropriate for binary
  functions that do not modify any of their
  operands
• Member functions are more appropriate for binary
  functions that do modify one of their operands

20
Data Type Conversions

• Types of possible conversions
• From built-in type to built-in type
• From built-in type to class type
• From class type to built-in type
• From class type to class type
• Built-in to built-in conversion can be implicit,
  or explicit using a cast
• Syntax for explicit conversion
• dataType(expression)

21
Data Type Conversions (continued)

• Built-in to class conversion
• can be done with a type conversion constructor
• Type conversion constructor a constructor whose
  first argument is not a member of its class its
  remaining arguments (if any) all have default
  values
• Type conversion constructor can be explicitly
  invoked after all objects have been declared

22
Data Type Conversions (continued)
23
Data Type Conversions (continued)

• Class to built-in conversion
• can be done with a conversion operator function
• Conversion operator function a member operator
  function with the name of a built-in data type or
  class
• When the name is that of a built-in data type, it
  converts from a class to a built-in data type
• Conversion operators have no explicit arguments
  and no explicit return type

24
Data Type Conversions (continued)
25
Data Type Conversions (continued)

• Class to class conversion
• also uses a conversion operator function, but the
  operator function uses the name of a class being
  converted to
• The operator function name determines the result
  of the conversion
• If two classes each have conversion operators for
  converting to the other class, a forward
  declaration to the second class is needed in the
  first class

26
Data Type Conversions (continued)
27
Applications

• Multi-Object Gas Pump Simulation
• Add a Customer class
• Create a multi-class simulation program using the
  Pump and Customer classes

28
Class Inheritance

• Inheritance the ability to derive one class from
  another class
• Base class the initial class used for
  derivation also called parent or superclass
• Derived class the class created from a base
  class also called child or subclass
• Derived class incorporates all data and member
  functions of its base class, but can add new or
  override existing data and member functions

29
Class Inheritance (continued)

• Simple inheritance each derived type has only
  one immediate base type

30
Class Inheritance (continued)

• Multiple inheritance a derived type has two or
  more base types

31
Class Inheritance (continued)

• Class hierarchies illustrate the order in which
  one class is derived from another
• Syntax for declaring a derived class
• class derivedClassName classAccess
  baseClassName

32
Access Specifications

• Access specifier private in base class precludes
  access by a derived class
• protected access in base class permits only
  member or friend functions, but allows derived
  class to specify its access

33
Access Specifications (continued)

• Derived class defines the inheritance subject to
  the base classs restriction, using the
  class-access specifier
• Inherited Access Restrictions

34
Class Inheritance (continued)
35
Class Inheritance (continued)
36
Class Inheritance (continued)

• A derived class object can be assigned to a base
  class object only the base class data members
  are actually assigned

37
Polymorphism

• Polymorphism the manipulation or overloading of
  preexisting objects to suit the current need
• Polymorphism permits the same function name to be
  used in both base and derived classes
• Static binding the decision of which function to
  use is made at compile time
• Dynamic binding the decision of which function
  to use is made at run time

38
Polymorphism (continued)

• Dynamic binding requires the use of virtual
  functions
• Virtual function creates a pointer to a
  function, but the pointer value is not assigned
  until the function is actually called
• At run time, the proper function will be selected
  based on the object making the call
• Use the virtual keyword to make a function virtual

39
Polymorphism (continued)
40
Polymorphism (continued)
41
Polymorphism (continued)
42
Polymorphism (continued)

• A virtual function remains virtual in the next
  derived class regardless of the use of the
  keyword virtual in the derived class
• All subsequent derived class override versions of
  a virtual function must have the same return type
  and parameter list

43
Polymorphism (continued)

• An inheritance diagram

44
Common Programming Errors

• Using a user-defined assignment operator in a
  multiple assignment expression when the operator
  was not defined to return an object
• Using the keyword friend when defining a friend
  function. The friend keyword should be used only
  within the class declaration section
• Using the keyword static when defining either a
  static data or function member (should be used in
  the class declaration section only)

45
Common Programming Errors (continued)

• Failing to instantiate static data members before
  creating class objects that access them
• Attempting to redefine an operators meaning for
  built-in data types
• Redefining an overloaded operator to perform a
  function not indicated by its conventional
  meaning (bad programming practice)

46
Common Programming Errors (continued)

• Attempting to make a conversion operator function
  a friend instead of a member function
• Attempting to specify a return type for a member
  conversion operator function
• Attempting to override a virtual function without
  using the same type and number of arguments
• Using the keyword virtual in the class
  implementation section (only used in the class
  declaration section)

47
Summary

• Assignment operator may be declared for a class
• Copy constructor initializes an object by using
  another object of the same class
• Class scope is defined by the pair of braces
• Each object has its own set of data members,
  except for static members which are shared
• Static functions apply to the whole class, and
  can only access static data members and other
  static function members

48
Summary (continued)

• Friend status allows a nonmember function to
  access a classs private data members
• User-defined operators can be constructed using
  member operator functions
• Operator functions may be friend functions
• Type conversion constructor its first argument
  is not a class member and its other arguments
  have default values
• Conversion operator function a member operator
  function with the name of a built-in data type or
  class

49
Summary (continued)

• Inheritance ability to derive one class from
  another
• Polymorphism ability to have the same function
  name invoke different functions based on the
  object making the call
• Static binding function to be used is determined
  at compile time
• Dynamic binding function to be used is
  determined at run time
• Virtual function designates that dynamic binding
  should be used