Object-oriented programming with C

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Lesson A
Template Functions
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Lesson A Objectives

• To learn
• How to create template functions
• How to use multiple parameters in a template
  function
• How to overload template functions

3
Lesson A Objectives

• To learn
• How to use more than one type in a template
  function
• How to explicitly specify the type in a template
  function
• How to use template functions with class objects

4
Creating Template Functions

• Template functions
• Allow you to write a single function that serves
  as an outline, or template, for a group of
  functions that differ in the types of parameters
  they use
• In a template function, at least one argument is
  generic, or parameterized

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int reverse(int x) return (-x) double
reverse(double x) return (-x) float
reverse(float x) return (-x)
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variableType reverse(variableType x) return
(-x)
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Creating Template Functions

• Before coding a template function, include a
  template definition with the following
  information
• The keyword template
• A left angle bracket (lt)
• A list of generic types, separated with commas if
  more than one type is needed
• A right angle bracket(gt)

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Creating Template Functions

• A family of functions
• A group of functions that is generated from the
  same template
• C allows you to define macros, which permit
  generic substitution
• However, macros are seldom recommended

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templateltclass Tgt T reverse(T x) return
(-x)
double amount-9.86 reverse(amount)
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Creating Template Functions

• Each generic type in the list of generic types
  has two parts
• The keyword class
• An identifier that represents the generic type
• Although any legal C identifier may be used for
  the type in the template function, many
  programmers prefer T (for Template)

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Creating Template Functions

• When you call a template function, a generated
  function that uses the appropriate type is
  created or instantiated
• The compiler generates code for as many different
  functions as it needs, depending on the function
  calls made
• The definition of the template function and the
  template function itself must reside in the
  source file

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Creating Template Functions

• You cant place the function definition and the
  function code in separate files because
• The function cant be compiled into object format
  without knowing the types
• The function wont know that it needs to
  recognize the types without the template
  definition

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includeltiostream.hgt includeltiomanip.hgt includelt
dos.hgt templateltclass Tgt void fillScreen(T
answer) int width5 for (int t0
tlt20t) coutltltsetw(width)ltltanswer
coutltlt"Another Teacher's Pet Sucess"ltltendl
widthwidth2
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void main() int iUseAns, iCorrectAns11 cou
tltlt"What is 47?" cingtgtiUseAns if(iUseAnsiCo
rrectAns) fillScreen(iUseAns)
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Using Multiple Parameters and Overloading
Function Templates

• Function templates may have more than one
  parameter
• You may overload function templates, as long as
  each version of the function takes different
  arguments, allowing the compiler to distinguish
  between them

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includeltiostream.hgt templateltclass Tgt T
larger(T x, T y) T big if (xgty)
bigx else bigy return(big)
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void main() int a7, b12 double c4.5,
d1.3 coutltltlarger(a,b)ltltendl coutltltlarger(c,d)lt
ltendl // coutltltlarger(a,c) errors
Overloading example
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includeltiostream.hgt templateltclass Tgt void
inverse(T x, T y) T temp tempx
xy ytemp templateltclass Tgt void
inverse(T x) x-x
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void main() double d13.4, d25.6 inverse(d1)
inverse(d1,d2) coutltltd1ltlt" "ltltd2ltltendl
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Using More Than One Type in a Template Function

• To create a template function that employs
  multiple types, you simply use a unique type
  identifier for each type
• The option of using multiple types in a template
  function may not be available on some older C
  compilers

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includeltiostream.hgt template ltclass T, class
Ugt void firstLarger(T val1, U val2) if (val1
gtval2) coutltlt"First is larger"ltltendl
else coutltlt"First is not larger"ltltendl v
oid main() firstLarger(2.1, 9) firstLarger('G',
12)
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Explicitly Specifying the Type in a Template
Function

• When you call a template function, the arguments
  to the function dictate the types to be used
• To override deduced types, you can explicitly
  code types within angle brackets immediately
  following the function name in the function call
• You can code empty angle brackets after the
  function name to indicate the types should be
  deduced and not overridden

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Explicitly Specifying the Type in a Template
Function

• Explicitly specifying a type is particularly
  useful when at least one of the types you need to
  parameterize or generate within the function is
  not an argument to the function
• The compiler can deduce the template function
  types only by using the values passed to the
  function

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includeltiostream.hgt templateltclass Tgt T
reverse(T x) return (-x) void main()
double amount45.65 coutltltreverse(amount)
coutltltreverseltdoublegt(amount)
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includeltiostream.hgt templateltclass T, class Ugt T
reverse (U x) return (-x) void main()
double amount-8.8 coutltltreverseltintgt(amount)
coutltltreverseltdoublegt(amount)ltltendl
coutltltreverseltintgt(amount)ltltendl
coutltltreverseltint,doublegt(amount)ltltendl
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Using Template Functions with Class Objects

• Template functions work as well with classes as
  they do with simple data types
• Your additional responsibility is to
• Ensure that any operations used within the
  template function have been defined for the class
  objects passed to the template functions

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includeltiostream.hgt templateltclass Tgt T
reverse(T x) return (-x) class
PhoneCall private int lengthOfCall
char billCode public
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PhoneCall(const int l, const char b)
PhoneCall PhoneCalloperator-(void) void
showCall(void) PhoneCallPhoneCall(const
int len0, const char b' ') PhoneCalllengthOf
Calllen PhoneCallbillCodeb void
PhoneCallshowCall(void) coutltlt"the code is
"ltltPhoneCallbillCodeltltendl
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PhoneCall PhoneCalloperator-(void)
PhoneCallbillCode'C' return
(this) void main() PhoneCall aCall(10,
'S') aCall.showCall() aCallreverse(aCall) a
Call.showCall()
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Lab Exercises and Homework

• Do Exercises 1 on page 347
• Do Exercises 2 on page 347
• Do Exercises 3 on page 347
• Due date

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Lesson B
Template Classes
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Lesson B Objectives

• To learn
• The advantages of using template classes
• How to create a complete class template
• How to create container classes

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Template Classes

• If you find it necessary to create several
  similar classes, you might consider developing a
  template class
• Template class
• Class in which at least one type is generic or
  parameterized
• It provides the outline for a family of similar
  classes

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Template Classes

• To create a template class
• Begin with the template definition
• Then write the class definition using the generic
  type or types in each instance for which a
  substitution should take place

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Template Classes

• Within a program, you can instantiate objects
  that have the class template type
• Add the desired type to the current class
  instantiation by placing its name between angle
  brackets following the generic class name

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templateltclass Tgt class Number private T
theNumber public Number(const T n)
void display(void)
Numberltintgt myValue
NumberltintgtmyValue(77)
Numberltdoublegt yourValue(3.46) yourValue.display(
)
myValue.display()
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Creating a Complete Class Template

• To use a template class member function, you use
  the dot operator with an instantiation of the
  class
• Some C programmers reserve the term class
  template to indicate the source code they write,
  using template class to refer to the actual
  generated class that exists for a specific type
  after C determines what type applies

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includeltiostream.hgt templateltclass Tgt class
Generic private T instance
public Generic(T i) void
print(void)
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//generic constructor templateltclass
Tgt GenericltTgtGeneric(T i0) Genericinstance
i templateltclass Tgt void GenericltTgtprint(vo
id) coutltlt"Generic orinting
"ltltendl coutltltGenericltTgtinstanceltltendl
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class Employee private int
idNum double salary public Employee(int
id) friend ostream operator
ltlt(ostream out, const Employee e)
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EmployeeEmployee(int id0) EmployeeidNumid
Employeesalary4.9 ostream
operatorltlt(ostream out, const Employee emp)
outltlt"Employee number "ltltemp.idNum outltlt"
Salary "ltltemp.salary return(out)
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void main() GenericltintgtanInt(7) Genericltdoub
legtsomeMoney(6.65) GenericltEmployeegt
aWorker(333) anInt.print() someMoney.print()
aWorker.print()
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Container Classes

• Many C compilers come with class libraries
  called container classes
• Container classes
• Template classes that have already been written
  to perform common class tasks
• The purpose of container classes is to manage
  groups of other classes

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Container Classes

• A common programming task is to create a linked
  list
• Linked list
• Chain of objects, each of which consists of at
  least two parts
• An object
• A pointer to another object

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Container Classes

• Many linked lists provide more than a pointer to
  the next logical object
• No matter what types of objects are linked,
  procedures must be developed to
• Establish links between objects
• Insert new member objects into appropriate spots
  within the linked list

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Container Classes

• A generic class that holds an object and a link,
  plus all linked list functions that handle the
  lists chores, is a useful tool when working with
  lists
• As such a class may be used with a number of
  other class objects
• The developers of C have already created such a
  container class - Its name is List

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Container Classes

• List
• Contains functions like add(), detach(), and
  getItem()
• List is a template class because the programmers
  who designed your compiler could not have
  predicted the exact characteristics of all
  classes you might create

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Container Classes

• Different compilers include different built-in
  classes
• Some compilers may not offer any container
  classes
• The more container classes your compiler
  supplies, the less you may find it necessary to
  write your own template classes
• Nevertheless, it is still beneficial to
  understand how its done

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includeltiostream.hgt templateltclass Tgt class
Array private T data int size
public Array(T d, int s) void
showList(void) void showFirst(void)
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template ltclass Tgt ArrayltTgtArray(T d, int s)
ArrayltTgtdatad ArrayltTgtsizes
templateltclass Tgt void ArrayltTgtshowList()
int szArrayltTgtsize coutltlt"Entire List
"ltltendl for(int x0 xltsz x)
coutltltArrayltTgtdataxltltendl
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templateltclass Tgt void ArrayltTgtshowFirst()
coutltlt"First element is " coutltltArrayltTgtdata
0ltltendl class Employee private int
idNum double salary public Employee(int
id) friend ostream operator
ltlt(ostream out, const Employee e)
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EmployeeEmployee(int id0) EmployeeidNumid
Employeesalary4.9 ostream operator
ltlt(ostream out, const Employee
emp) outltlt"Employee number
"ltltemp.idNum outltlt" Salary "ltltemp.salary retur
n(out)
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void main() int vals422,33,44,55
Arrayltintgtval(vals, sizeof(vals)/sizeof(vals0))
Employee workers6110, 220, 330, 440,
550, 660 ArrayltEmployeegt worker(workers,
sizeof(workers)/sizeof(workers0))
val.showList() val.showFirst()
worker.showList() worker.showFirst()
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Lab Exercises and Homework

• Do Exercises 1 on page 358
• Do Exercises 2 on page 358
• Do Exercises 3 on page 358
• Due date