1
Structured Types,Data
Abstraction and Classes
2
Chapter 11 Topics
Meaning of a Structured Data Type
Declaring and Using a struct Data Type
C++ union Data Type
Meaning of an Abstract Data Type
Declaring and Using a class Data Type
Using Separate Specification and
Implementation Files
Invoking class Member Functions in Client
Code
C++ class Constructors
3
C++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
4
Structured Data Type
A structured data type is a type in which
each value is a collection of component
items,
the entire collection has a single name
each component can be accessed
individually
5
C++ Structured Type
often we have related information of
various types that we?d like to store
together for convenient access under
the same identifier,for example,,,
6
thisAnimal
5000
.id 2037581
.name,giant panda”
.genus,Ailuropoda”
.species,melanoluka”
.country,China”
.age 18
.weight 234.6
.health Good
7
anotherAnimal
6000
.id 5281003
.name,llama”
.genus,Lama”
.species,peruana”
.country,Peru”
.age 7
.weight 278.5
.health Excellent
8
struct AnimalType
enum HealthType { Poor,Fair,Good,Excellent } ;
struct AnimalType // declares a struct data type
{ // does not allocate memory
long id ;
string name ;
string genus ;
string species ; struct members
string country ;
int age ;
float weight ;
HealthType health ;
} ;
AnimalType thisAnimal ; // declare variables of AnimalType
AnimalType anotherAnimal ;
9
struct type Declaration
SYNTAX
struct TypeName // does not allocate memory
{
MemberList
} ; // ends with a semicolon
MemberList SYNTAX
DataType MemberName ;
DataType MemberName ;
,
.
.
10
struct type Declaration
The struct declaration names a type and names the
members of the struct.
Note that each member name is given a type.
Also,member names must be unique within a struct
type.
It does not allocate memory when you make a struct
declaration.
None of the struct members are associated with
memory until we declare a struct variable.
11
More about
struct type declarations
If the struct type declaration precedes all functions it
will be visible throughout the rest of the file,
If it is placed within a function,only that function can
use it.
It is common to place struct type declarations with
TypeNames in a (.h) header file and #include that file.
It is possible for members of different struct types to
have the same identifiers,
Also a non-struct variable may have the same
identifier as a structure member.
12
Accessing struct Members
Dot ( period ) is the member selection operator.
After the struct type declaration,the various members
can be used in your program only when they are
preceded by a struct variable name and a dot.
EXAMPLES
thisAnimal.weight
anotherAnimal.country
13
Valid operations on a struct member
depend only on its type
thisAnimal.age = 18;
thisAnimal.id = 2037581;
cin >> thisAnimal.weight;
getline ( cin,thisAnimal.species );
thisAnimal.name =,giant panda”;
thisAnimal.genus[ 0 ] = toupper (thisAnimal.genus[ 0 ] ) ;
thisAnimal.age++;
14
Aggregate Operation
is an operation on a data structure as
a whole,as opposed to an operation
on an individual component of the
data structure
15
Aggregate struct Operations
I/O,arithmetic,and comparisons of entire struct
variables are NOT ALLOWED!
valid operations on an entire struct type variable:
i,assignment to another struct variable of same type
ii,pass to a function as argument
(by value or by reference)
iii.return as value of a function
16
Examples of
aggregate struct operations
anotherAnimal = thisAnimal ; // assignment
WriteOut(thisAnimal); // value parameter
ChangeAge(thisAnimal); // reference parameter
thisAnimal = GetAnimalData( ); // return value of function
NOW WE?LL WRITE THE 3 FUNCTIONS USED HERE,,,
17
void WriteOut( /* in */ AnimalType thisAnimal)
// Prints out values of all members of thisAnimal
// Precondition,all members of thisAnimal are assigned
// Postcondition,all members have been written out
{
cout <<,ID #,<< thisAnimal.id << thisAnimal.name << endl ;
cout << thisAnimal.genus << thisAnimal.species << endl ;
cout << thisAnimal.country << endl ;
cout << thisAnimal.age <<,years,<< endl ;
cout << thisAnimal.weight <<,lbs.,<< endl ;
cout <<,General health,,;
WriteWord ( thisAnimal.health ) ;
}
18
void ChangeAge ( /* inout */ AnimalType& thisAnimal )
// Adds 1 to age
// Precondition,thisAnimal.age is assigned
// Postcondition,thisAnimal.age == thisAnimal.age@entry + 1
{
thisAnimal.age++ ;
}
Passing a struct Type by Reference
19
AnimalType GetAnimalData ( void )
// Obtains all information about an animal from keyboard
// Postcondition:
// Function value == AnimalType members entered at kbd
{
AnimalType thisAnimal ;
char response ;
do { // have user enter all members until they are correct
.
.
.
} while (response !=?Y? ) ;
return thisAnimal ;
}
20
Hierarchical Structures
The type of a struct member can be
another struct type,This is called
nested or hierarchical structures.
Hierarchical structures are very useful
when there is much detailed
information in each record.
FOR EXAMPLE,,,
21
struct MachineRec
Information about each machine in a shop contains:
an idNumber,
a written description,
the purchase date,
the cost,
and a history (including failure rate,number of
days down,and date of last service).
22
struct DateType
{ int month ; // Assume 1,,12
int day ; // Assume 1,,31
int year ; // Assume 1900,,2050
};
struct StatisticsType
{ float failRate ;
DateType lastServiced ; // DateType is a struct type
int downDays ;
} ;
struct MachineRec
{ int idNumber ;
string description ;
StatisticsType history ; // StatisticsType is a struct type
DateType purchaseDate ;
float cost ;
} ;
MachineRec machine ;
23
struct type variable machine
7000
.idNumber,description,history,purchaseDate,cost
.month,day,year
5719,DRILLING…” 3 21 1995 8000.0
.failrate,lastServiced,downdays
.02 1 25 1999 4
.month,day,year
machine.history.lastServiced.year has value 1999
24
Unions in C++
DEFINITION
A union is a struct that holds only one of its members
at a time during program execution.
EXAMPLE
union WeightType
{
long wtInOunces ;
int wtInPounds; only one at a time
float wtInTons;
} ;
25
Using Unions
union WeightType // declares a union type
{
long wtInOunces ;
int wtInPounds;
float wtInTons;
} ;
WeightType weight; // declares a union variable
weight.wtInTons = 4.83 ;
// Weight in tons is no longer needed,Reuse the memory space.
weight.wtInPounds = 35;
26
Abstraction
is the separation of the essential qualities of an object
from the details of how it works or is composed
focuses on what,not how
is necessary for managing large,complex software
projects
There are two important abstraction techniques,
control abstraction and data abstraction
27
Control Abstraction
separates the logical properties of an
action from its implementation
.
.
.
Search (list,item,length,where,found);
.
.
.
the function call depends on the
function?s specification (description),
not its implementation (algorithm)
28
Data Abstraction
separates the logical properties of a
data type from its implementation
LOGICAL PROPERTIES IMPLEMENTATION
What are the possible values? How can this be done in C++?
What operations will be needed? How can data types be used?
29
Data Type
set of values
(domain)
allowable operations
on those values
FOR EXAMPLE,data type int has
domain
-32768,,,32767
operations
+,-,*,/,%,>>,<<
30
Abstract Data Type (ADT)
a data type whose properties (domain
and operations) are specified (what)
independently of any particular
implementation (how)
FOR EXAMPLE,,,
31
ADT Specification Example
TYPE
TimeType
DOMAIN
Each TimeType value is a time in hours,minutes,
and seconds.
OPERATIONS
Set the time
Print the time
Increment by one second
Compare 2 times for equality
Determine if one time is,less than” another
32
Another ADT Specification
TYPE
ComplexNumberType
DOMAIN
Each value is an ordered pair of real numbers (a,b)
representing a + bi.
OPERATIONS
Initialize the complex number
Write the complex number
Add
Subtract
Multiply
Divide
Determine the absolute value of a complex number
33
ADT Implementation means
choosing a specific(concrete) data representation
for the abstract data using data types that already
exist (built-in or programmer-defined)
writing functions for each allowable operation
34
10 45 27
Several Possible Representations
of TimeType
3 int variables
3 strings
3-element int array
10 45 27
,10”,45”,27”
35
Some Possible Representations
of ComplexNumberType
struct with 2 float members
2-element float array
-16.2 5.8
-16.2 5.8
.real,imag
36
Data representation (Cont.)
Data representation
The concrete form of data used to represent
the abstract values of an abstract data type.
actual choice of representation depends on
time,space,and algorithms needed to
implement operations
37
C++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
38
class TimeType Specification
// SPECIFICATION FILE ( timetype.h )
class TimeType // declares a class data type
{ // does not allocate memory
public,// 5 public function members
void Set ( int hours,int mins,int secs ) ;
void Increment ( ) ;
void Write ( ) const ;
bool Equal ( TimeType otherTime ) const ;
bool LessThan ( TimeType otherTime ) const ;
private,// 3 private data members
int hrs ;
int mins ;
int secs ;
} ;
39
Use of C++ data Type class
facilitates re-use of C++ code for an ADT
software that uses the class is called a
client
variables of the class type are called class
objects or class instances
client code uses public member functions
to handle its class objects
40
Client Code Using TimeType
#include,timetype.h” // includes specification of the class
using namespace std ;
int main ( )
{
TimeType currentTime ; // declares 2 objects of TimeType
TimeType endTime ;
bool done = false ;
currentTime.Set ( 5,30,0 ) ;
endTime.Set ( 18,30,0 ) ;
while ( ! done )
{,,,
currentTime.Increment ( ) ;
if ( currentTime.Equal ( endTime ) )
done = true ;
}
}
41
class type Declaration
The class declaration creates a data type and
names the members of the class.
It does not allocate memory for any variables of
that type when we make a class declaration!
Client code still needs to declare class variables.
42
C++ Data Type class represents
an ADT
2 kinds of class members,
data members and function members
class members are private by default
data members are generally private
function members are generally declared public
private class members can be accessed only by
the class member functions (and friend functions),
not by client code.
43
Aggregate class Operations
built-in operations valid on class objects are:
i,member selection using dot (,) operator
ii,assignment to another class variable using ( = )
iii,pass to a function as argument
(by value or by reference)
iv,return as a value of a function
other operations can be defined as class member
functions
44
2 separate files Generally Used
for class Type
// SPECIFICATION FILE (Timetype,h )
// Specifies the data and function members.
class TimeType
{
public:
.,,
private:
.,,
} ;
// IMPLEMENTATION FILE ( Timetype.cpp )
// Implements the TimeType member functions,
.,,
45
Implementation File for
TimeType
// IMPLEMENTATION FILE ( Timetype.cpp )
// Implements the TimeType member functions,
#include,timetype.h” // also must appear in client code
#include <iostream>
.,,
bool TimeType,,Equal ( /* in */ TimeType otherTime ) const
// Postcondition,
// Function value == true,if this time equals otherTime
// == false,otherwise
{
return ( (hrs == otherTime.hrs) && (mins == otherTime.mins)
&& (secs == otherTime.secs) ) ;
}
.,,
46
Familiar Class Instances and
Function Members
the member selection operator (,) selects either data
members or function members
header files iostream and fstream declare the istream,
ostream,and ifstream,ofstream I/O classes
both cin and cout are class objects and get and ignore
are function members
cin.get (someChar) ;
cin.ignore (100,?\n?) ;
these statements declare myInfile as an instance of
class ifstream and invoke function member open
ifstream myInfile ;
myInfile.open (,A:\\mydata.dat” ) ;
47
Information Hiding
Class implementation details are hidden from the
client?s view,This is called information hiding.
Public functions of a class provide the interface
between the client code and the class objects.
client
code specification implementation
48
Scope Resolution Operator (,,)
C++ programs typically use several class types
different classes can have member functions with the
same identifier,like Write( )
member selection operator is used to determine the
class whose member function Write( ) is invoked
currentTime,Write( ) ; // class TimeType
numberZ,Write( ) ; // class ComplexNumberType
in the implementation file,the scope resolution
operator is used in the heading before the function
member?s name to specify its class
void TimeType,,Write ( ) const
{,,,
}
49
TimeType Class Instance
Diagrams
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
17
58
2
18
30
0
currentTime endTime
50
Use of const with
Member Functions
when a member function does not modify
the private data members,use const in both
the function prototype (in specification file)
and the heading of the function definition (in
implementation file)
51
Example Using const with
a Member Function
void TimeType,,Write ( ) const
// Postcondition,Time has been output in form HH:MM:SS
{ if ( hrs < 10 )
cout <<?0? ;
cout << hrs <<?:? ;
if ( mins < 10 )
cout <<?0? ;
cout << mins <<?:? ;
if ( secs < 10 )
cout <<?0? ;
cout << secs ;
}
52
Separate Compilation and
Linking of Files
timetype.h
client.cpp timetype.cpp
client.obj
client.exe
timetype.obj
Compiler Compiler
Linker
#include,timetype.h”
implementation file
specification file
main program
53
often several program files use the same header file
containing typedef statements,constants,or class
type declarations--but,it is a compile-time error to
define the same identifier twice
this preprocessor directive syntax is used to avoid
the compilation error that would otherwise occur from
multiple uses of #include for the same header file
#ifndef Preprocessor_Identifier
#define Preprocessor_Identifier
.
.
.
#endif
Avoiding Multiple Inclusion of
Header Files
54
Example Using Preprocessor
Directive #ifndef
// timetype,h FOR COMPILATION THE CLASS DECLARATION IN
// SPECIFICATION FILE FILE timetype.h WILL BE INCLUDED ONLY ONCE
#ifndef TIME_H
#define TIME_H // timetype,cpp // client.cpp
// IMPLEMENTATION FILE // Appointment program
class TimeType
{ #include,timetype.h” #include,timetype.h”
public:
.,,,,,int main ( void )
{
private,.,,
.,,}
} ;
#endif
55
Class Constructors
a class constructor is a member function whose purpose
is to initialize the private data members of a class object
the name of a constructor is always the same name of
the class,and there is no return type for the constructor
a class may have several constructors with different
parameter lists,A constructor with no parameters is the
default constructor
a constructor is implicitly invoked when a class object is
declared--if there are parameters,their values are listed
in parentheses in the declaration
56
Specification of TimeType
Class Constructors
class TimeType // timetype.h
{
public,// 7 function members
void Set ( int hours,int minutes,int seconds ) ;
void Increment ( ) ;
void Write ( ) const ;
bool Equal ( TimeType otherTime ) const ;
bool LessThan ( TimeType otherTime ) const ;
TimeType ( int initHrs,int initMins,int initSecs ) ; // constructor
TimeType ( ) ; // default constructor
private,// 3 data members
int hrs ;
int mins ;
int secs ;
} ;
57
Implementation of TimeType
Default Constructor
TimeType,,TimeType ( )
// Default Constructor
// Postcondition,
// hrs == 0 && mins == 0 && secs == 0
{
hrs = 0 ;
mins = 0 ;
secs = 0 ;
}
58
Implementation of Another
TimeType Class Constructor
TimeType,,TimeType ( /* in */ int initHrs,
/* in */ int initMins,
/* in */ int initSecs )
// Constructor
// Precondition,0 <= initHrs <= 23 && 0 <= initMins <= 59
// 0 <= initSecs <= 59
// Postcondition:
// hrs == initHrs && mins == initMins && secs == initSecs
{
hrs = initHrs ;
mins = initMins ;
secs = initSecs ;
}
59
Automatic invocation of
constructors occurs
TimeType departureTime ; // default constructor invoked
TimeType movieTime (19,30,0 ) ; // parameterized constructor
departureTime movieTime
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
0
0
0
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
19
30
0
60
Class Destructor
Just as a constructor is implicitly invoked when
a class object is created,a destructor is implicitly
invoked when a class object is destroyed.
A class destructor is named the same as a
constructor except that the first character is a
tilde(~):
61
Class SomeClass
{
public:
:
SomeClass( ); //Constructor
~SomeClass( ); //Destructor
private:
:
};
Example
Structured Types,Data
Abstraction and Classes
2
Chapter 11 Topics
Meaning of a Structured Data Type
Declaring and Using a struct Data Type
C++ union Data Type
Meaning of an Abstract Data Type
Declaring and Using a class Data Type
Using Separate Specification and
Implementation Files
Invoking class Member Functions in Client
Code
C++ class Constructors
3
C++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
4
Structured Data Type
A structured data type is a type in which
each value is a collection of component
items,
the entire collection has a single name
each component can be accessed
individually
5
C++ Structured Type
often we have related information of
various types that we?d like to store
together for convenient access under
the same identifier,for example,,,
6
thisAnimal
5000
.id 2037581
.name,giant panda”
.genus,Ailuropoda”
.species,melanoluka”
.country,China”
.age 18
.weight 234.6
.health Good
7
anotherAnimal
6000
.id 5281003
.name,llama”
.genus,Lama”
.species,peruana”
.country,Peru”
.age 7
.weight 278.5
.health Excellent
8
struct AnimalType
enum HealthType { Poor,Fair,Good,Excellent } ;
struct AnimalType // declares a struct data type
{ // does not allocate memory
long id ;
string name ;
string genus ;
string species ; struct members
string country ;
int age ;
float weight ;
HealthType health ;
} ;
AnimalType thisAnimal ; // declare variables of AnimalType
AnimalType anotherAnimal ;
9
struct type Declaration
SYNTAX
struct TypeName // does not allocate memory
{
MemberList
} ; // ends with a semicolon
MemberList SYNTAX
DataType MemberName ;
DataType MemberName ;
,
.
.
10
struct type Declaration
The struct declaration names a type and names the
members of the struct.
Note that each member name is given a type.
Also,member names must be unique within a struct
type.
It does not allocate memory when you make a struct
declaration.
None of the struct members are associated with
memory until we declare a struct variable.
11
More about
struct type declarations
If the struct type declaration precedes all functions it
will be visible throughout the rest of the file,
If it is placed within a function,only that function can
use it.
It is common to place struct type declarations with
TypeNames in a (.h) header file and #include that file.
It is possible for members of different struct types to
have the same identifiers,
Also a non-struct variable may have the same
identifier as a structure member.
12
Accessing struct Members
Dot ( period ) is the member selection operator.
After the struct type declaration,the various members
can be used in your program only when they are
preceded by a struct variable name and a dot.
EXAMPLES
thisAnimal.weight
anotherAnimal.country
13
Valid operations on a struct member
depend only on its type
thisAnimal.age = 18;
thisAnimal.id = 2037581;
cin >> thisAnimal.weight;
getline ( cin,thisAnimal.species );
thisAnimal.name =,giant panda”;
thisAnimal.genus[ 0 ] = toupper (thisAnimal.genus[ 0 ] ) ;
thisAnimal.age++;
14
Aggregate Operation
is an operation on a data structure as
a whole,as opposed to an operation
on an individual component of the
data structure
15
Aggregate struct Operations
I/O,arithmetic,and comparisons of entire struct
variables are NOT ALLOWED!
valid operations on an entire struct type variable:
i,assignment to another struct variable of same type
ii,pass to a function as argument
(by value or by reference)
iii.return as value of a function
16
Examples of
aggregate struct operations
anotherAnimal = thisAnimal ; // assignment
WriteOut(thisAnimal); // value parameter
ChangeAge(thisAnimal); // reference parameter
thisAnimal = GetAnimalData( ); // return value of function
NOW WE?LL WRITE THE 3 FUNCTIONS USED HERE,,,
17
void WriteOut( /* in */ AnimalType thisAnimal)
// Prints out values of all members of thisAnimal
// Precondition,all members of thisAnimal are assigned
// Postcondition,all members have been written out
{
cout <<,ID #,<< thisAnimal.id << thisAnimal.name << endl ;
cout << thisAnimal.genus << thisAnimal.species << endl ;
cout << thisAnimal.country << endl ;
cout << thisAnimal.age <<,years,<< endl ;
cout << thisAnimal.weight <<,lbs.,<< endl ;
cout <<,General health,,;
WriteWord ( thisAnimal.health ) ;
}
18
void ChangeAge ( /* inout */ AnimalType& thisAnimal )
// Adds 1 to age
// Precondition,thisAnimal.age is assigned
// Postcondition,thisAnimal.age == thisAnimal.age@entry + 1
{
thisAnimal.age++ ;
}
Passing a struct Type by Reference
19
AnimalType GetAnimalData ( void )
// Obtains all information about an animal from keyboard
// Postcondition:
// Function value == AnimalType members entered at kbd
{
AnimalType thisAnimal ;
char response ;
do { // have user enter all members until they are correct
.
.
.
} while (response !=?Y? ) ;
return thisAnimal ;
}
20
Hierarchical Structures
The type of a struct member can be
another struct type,This is called
nested or hierarchical structures.
Hierarchical structures are very useful
when there is much detailed
information in each record.
FOR EXAMPLE,,,
21
struct MachineRec
Information about each machine in a shop contains:
an idNumber,
a written description,
the purchase date,
the cost,
and a history (including failure rate,number of
days down,and date of last service).
22
struct DateType
{ int month ; // Assume 1,,12
int day ; // Assume 1,,31
int year ; // Assume 1900,,2050
};
struct StatisticsType
{ float failRate ;
DateType lastServiced ; // DateType is a struct type
int downDays ;
} ;
struct MachineRec
{ int idNumber ;
string description ;
StatisticsType history ; // StatisticsType is a struct type
DateType purchaseDate ;
float cost ;
} ;
MachineRec machine ;
23
struct type variable machine
7000
.idNumber,description,history,purchaseDate,cost
.month,day,year
5719,DRILLING…” 3 21 1995 8000.0
.failrate,lastServiced,downdays
.02 1 25 1999 4
.month,day,year
machine.history.lastServiced.year has value 1999
24
Unions in C++
DEFINITION
A union is a struct that holds only one of its members
at a time during program execution.
EXAMPLE
union WeightType
{
long wtInOunces ;
int wtInPounds; only one at a time
float wtInTons;
} ;
25
Using Unions
union WeightType // declares a union type
{
long wtInOunces ;
int wtInPounds;
float wtInTons;
} ;
WeightType weight; // declares a union variable
weight.wtInTons = 4.83 ;
// Weight in tons is no longer needed,Reuse the memory space.
weight.wtInPounds = 35;
26
Abstraction
is the separation of the essential qualities of an object
from the details of how it works or is composed
focuses on what,not how
is necessary for managing large,complex software
projects
There are two important abstraction techniques,
control abstraction and data abstraction
27
Control Abstraction
separates the logical properties of an
action from its implementation
.
.
.
Search (list,item,length,where,found);
.
.
.
the function call depends on the
function?s specification (description),
not its implementation (algorithm)
28
Data Abstraction
separates the logical properties of a
data type from its implementation
LOGICAL PROPERTIES IMPLEMENTATION
What are the possible values? How can this be done in C++?
What operations will be needed? How can data types be used?
29
Data Type
set of values
(domain)
allowable operations
on those values
FOR EXAMPLE,data type int has
domain
-32768,,,32767
operations
+,-,*,/,%,>>,<<
30
Abstract Data Type (ADT)
a data type whose properties (domain
and operations) are specified (what)
independently of any particular
implementation (how)
FOR EXAMPLE,,,
31
ADT Specification Example
TYPE
TimeType
DOMAIN
Each TimeType value is a time in hours,minutes,
and seconds.
OPERATIONS
Set the time
Print the time
Increment by one second
Compare 2 times for equality
Determine if one time is,less than” another
32
Another ADT Specification
TYPE
ComplexNumberType
DOMAIN
Each value is an ordered pair of real numbers (a,b)
representing a + bi.
OPERATIONS
Initialize the complex number
Write the complex number
Add
Subtract
Multiply
Divide
Determine the absolute value of a complex number
33
ADT Implementation means
choosing a specific(concrete) data representation
for the abstract data using data types that already
exist (built-in or programmer-defined)
writing functions for each allowable operation
34
10 45 27
Several Possible Representations
of TimeType
3 int variables
3 strings
3-element int array
10 45 27
,10”,45”,27”
35
Some Possible Representations
of ComplexNumberType
struct with 2 float members
2-element float array
-16.2 5.8
-16.2 5.8
.real,imag
36
Data representation (Cont.)
Data representation
The concrete form of data used to represent
the abstract values of an abstract data type.
actual choice of representation depends on
time,space,and algorithms needed to
implement operations
37
C++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
38
class TimeType Specification
// SPECIFICATION FILE ( timetype.h )
class TimeType // declares a class data type
{ // does not allocate memory
public,// 5 public function members
void Set ( int hours,int mins,int secs ) ;
void Increment ( ) ;
void Write ( ) const ;
bool Equal ( TimeType otherTime ) const ;
bool LessThan ( TimeType otherTime ) const ;
private,// 3 private data members
int hrs ;
int mins ;
int secs ;
} ;
39
Use of C++ data Type class
facilitates re-use of C++ code for an ADT
software that uses the class is called a
client
variables of the class type are called class
objects or class instances
client code uses public member functions
to handle its class objects
40
Client Code Using TimeType
#include,timetype.h” // includes specification of the class
using namespace std ;
int main ( )
{
TimeType currentTime ; // declares 2 objects of TimeType
TimeType endTime ;
bool done = false ;
currentTime.Set ( 5,30,0 ) ;
endTime.Set ( 18,30,0 ) ;
while ( ! done )
{,,,
currentTime.Increment ( ) ;
if ( currentTime.Equal ( endTime ) )
done = true ;
}
}
41
class type Declaration
The class declaration creates a data type and
names the members of the class.
It does not allocate memory for any variables of
that type when we make a class declaration!
Client code still needs to declare class variables.
42
C++ Data Type class represents
an ADT
2 kinds of class members,
data members and function members
class members are private by default
data members are generally private
function members are generally declared public
private class members can be accessed only by
the class member functions (and friend functions),
not by client code.
43
Aggregate class Operations
built-in operations valid on class objects are:
i,member selection using dot (,) operator
ii,assignment to another class variable using ( = )
iii,pass to a function as argument
(by value or by reference)
iv,return as a value of a function
other operations can be defined as class member
functions
44
2 separate files Generally Used
for class Type
// SPECIFICATION FILE (Timetype,h )
// Specifies the data and function members.
class TimeType
{
public:
.,,
private:
.,,
} ;
// IMPLEMENTATION FILE ( Timetype.cpp )
// Implements the TimeType member functions,
.,,
45
Implementation File for
TimeType
// IMPLEMENTATION FILE ( Timetype.cpp )
// Implements the TimeType member functions,
#include,timetype.h” // also must appear in client code
#include <iostream>
.,,
bool TimeType,,Equal ( /* in */ TimeType otherTime ) const
// Postcondition,
// Function value == true,if this time equals otherTime
// == false,otherwise
{
return ( (hrs == otherTime.hrs) && (mins == otherTime.mins)
&& (secs == otherTime.secs) ) ;
}
.,,
46
Familiar Class Instances and
Function Members
the member selection operator (,) selects either data
members or function members
header files iostream and fstream declare the istream,
ostream,and ifstream,ofstream I/O classes
both cin and cout are class objects and get and ignore
are function members
cin.get (someChar) ;
cin.ignore (100,?\n?) ;
these statements declare myInfile as an instance of
class ifstream and invoke function member open
ifstream myInfile ;
myInfile.open (,A:\\mydata.dat” ) ;
47
Information Hiding
Class implementation details are hidden from the
client?s view,This is called information hiding.
Public functions of a class provide the interface
between the client code and the class objects.
client
code specification implementation
48
Scope Resolution Operator (,,)
C++ programs typically use several class types
different classes can have member functions with the
same identifier,like Write( )
member selection operator is used to determine the
class whose member function Write( ) is invoked
currentTime,Write( ) ; // class TimeType
numberZ,Write( ) ; // class ComplexNumberType
in the implementation file,the scope resolution
operator is used in the heading before the function
member?s name to specify its class
void TimeType,,Write ( ) const
{,,,
}
49
TimeType Class Instance
Diagrams
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
17
58
2
18
30
0
currentTime endTime
50
Use of const with
Member Functions
when a member function does not modify
the private data members,use const in both
the function prototype (in specification file)
and the heading of the function definition (in
implementation file)
51
Example Using const with
a Member Function
void TimeType,,Write ( ) const
// Postcondition,Time has been output in form HH:MM:SS
{ if ( hrs < 10 )
cout <<?0? ;
cout << hrs <<?:? ;
if ( mins < 10 )
cout <<?0? ;
cout << mins <<?:? ;
if ( secs < 10 )
cout <<?0? ;
cout << secs ;
}
52
Separate Compilation and
Linking of Files
timetype.h
client.cpp timetype.cpp
client.obj
client.exe
timetype.obj
Compiler Compiler
Linker
#include,timetype.h”
implementation file
specification file
main program
53
often several program files use the same header file
containing typedef statements,constants,or class
type declarations--but,it is a compile-time error to
define the same identifier twice
this preprocessor directive syntax is used to avoid
the compilation error that would otherwise occur from
multiple uses of #include for the same header file
#ifndef Preprocessor_Identifier
#define Preprocessor_Identifier
.
.
.
#endif
Avoiding Multiple Inclusion of
Header Files
54
Example Using Preprocessor
Directive #ifndef
// timetype,h FOR COMPILATION THE CLASS DECLARATION IN
// SPECIFICATION FILE FILE timetype.h WILL BE INCLUDED ONLY ONCE
#ifndef TIME_H
#define TIME_H // timetype,cpp // client.cpp
// IMPLEMENTATION FILE // Appointment program
class TimeType
{ #include,timetype.h” #include,timetype.h”
public:
.,,,,,int main ( void )
{
private,.,,
.,,}
} ;
#endif
55
Class Constructors
a class constructor is a member function whose purpose
is to initialize the private data members of a class object
the name of a constructor is always the same name of
the class,and there is no return type for the constructor
a class may have several constructors with different
parameter lists,A constructor with no parameters is the
default constructor
a constructor is implicitly invoked when a class object is
declared--if there are parameters,their values are listed
in parentheses in the declaration
56
Specification of TimeType
Class Constructors
class TimeType // timetype.h
{
public,// 7 function members
void Set ( int hours,int minutes,int seconds ) ;
void Increment ( ) ;
void Write ( ) const ;
bool Equal ( TimeType otherTime ) const ;
bool LessThan ( TimeType otherTime ) const ;
TimeType ( int initHrs,int initMins,int initSecs ) ; // constructor
TimeType ( ) ; // default constructor
private,// 3 data members
int hrs ;
int mins ;
int secs ;
} ;
57
Implementation of TimeType
Default Constructor
TimeType,,TimeType ( )
// Default Constructor
// Postcondition,
// hrs == 0 && mins == 0 && secs == 0
{
hrs = 0 ;
mins = 0 ;
secs = 0 ;
}
58
Implementation of Another
TimeType Class Constructor
TimeType,,TimeType ( /* in */ int initHrs,
/* in */ int initMins,
/* in */ int initSecs )
// Constructor
// Precondition,0 <= initHrs <= 23 && 0 <= initMins <= 59
// 0 <= initSecs <= 59
// Postcondition:
// hrs == initHrs && mins == initMins && secs == initSecs
{
hrs = initHrs ;
mins = initMins ;
secs = initSecs ;
}
59
Automatic invocation of
constructors occurs
TimeType departureTime ; // default constructor invoked
TimeType movieTime (19,30,0 ) ; // parameterized constructor
departureTime movieTime
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
0
0
0
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
19
30
0
60
Class Destructor
Just as a constructor is implicitly invoked when
a class object is created,a destructor is implicitly
invoked when a class object is destroyed.
A class destructor is named the same as a
constructor except that the first character is a
tilde(~):
61
Class SomeClass
{
public:
:
SomeClass( ); //Constructor
~SomeClass( ); //Destructor
private:
:
};
Example
