classes and objects · classes and objects class declaration class members data constructors...

www.sahajsolns.com

Chapter 4Chapter 4

OOPS WITH C++ 1Sahaj Computer Solutions

www.sahajsolns.com

Session Objectives� Classes and Objects

� Class Declaration

� Class Members

Data Constructors� Data Constructors

� Destructors

� Member Functions

� Class Member Visibility

� Private, Public,Protected

� The scope of the class object constructor

OOPS WITH C++ Sahaj Computer Solutions 2

www.sahajsolns.com

Session objectives� Default Constructor

� Constructor with arguments

� Constructor with default arguments

Dynamic constructor� Dynamic constructor

� Copy Constructor

� Overloaded Constructor

� Objects as Function arguments

� Member functions defined outside the class.

� Objects as arguments


www.sahajsolns.com

Session Objectives� Returning objects from functions

� Class array as class member data

� Array of objects

String as class member.� String as class member.


www.sahajsolns.com

Accessing Class Members� To access the members of the class we make use of the

DOT(.) Operator.

� Syntax:

Object-name.function-name(actual arguments)Object-name.function-name(actual arguments)

� Example:

� x.getData(100,75.5);


www.sahajsolns.com

Defining Member Functions� Member functions can be defined in two places.

� Outside the Class definition

� Inside the class definition

� Outside the Class Definition� Outside the Class Definition

� Member functions that are declared inside the class have to e defined separately outside the class.

� Their definition is much like normal functions.

� They should have a function header and a body.


www.sahajsolns.com

Outside the Class Definition� An important difference between a member function and a

normal function is that a member function incorporates a membership ‘identity label’ in the header.

� This label tells the compiler which class the function � This label tells the compiler which class the function belongs to.

� The general form of a member-function definition is :

return-type class-name:: function-name(argument declaration)

{

Function-Body

}


www.sahajsolns.com

Outside the Class Definition� The membership label class-name:: tells the compiler

that the function-name belongs to the class-name .

� That is the scope of the function is restricted to the class name specified in the header line.class name specified in the header line.

� The symbol :: is called the scope resolution operator.

� Example:void sum::getdata(int a,int b)

{

sum=a+b;

}


www.sahajsolns.com

Defining Member Functions� The member functions have some special

characteristics that are often used in the program development:

� Several different classes can use the same function � Several different classes can use the same function name. The membership label will resolve their scope.

� Member functions can access the private data of the class. A non-member function cannot do so.

� A member function can call another member function directly, without using the dot operator.


www.sahajsolns.com

Inside the class definition� Another method of

declaring a member function is to replace the function definition by the actual definition.

� Example

class sum{

int a,b;

public:the actual definition. public:

void getdata(int x,int y)

{

a=x;

b=y

}

};


www.sahajsolns.com

Making Outside function Inline� A member function outside the class definition can still be

made inline by using the qualifier inline.� Example:

class item{::::::::::::::::::::::::::::::::::::public:

void getdata(int a,int b);};

inline void item::getdata(int a,int b){

::::::::::::::::::::::}


www.sahajsolns.com

Nesting Member Functions� As discussed earlier a member function of a class can

be called by an object of that class using the dot operator.

� However there is an exception to this. � However there is an exception to this.

� A member function can be called by using its name inside another member function of that same class.

� This is known as nesting of member functions

� Program:CH4PG7.cpp


www.sahajsolns.com

Arrays within a class� Arrays can be used as member variables in a class

� For example:

class arraydemo{

int a[20];int a[20];

public:

void getval(){

for(int i=0;i<n;i++)

cin>>a[i];

}

};


Program: CH4PG8.cpp

www.sahajsolns.com

Memory Allocation for ObjectsMember variable 1

Member variable 2

Member function1

Class


Member variable 1

Member variable 2

Member variable 1

Member variable 2

Member variable 1

Member variable 2

Member function1

Member function2

Object A Object B Object C

www.sahajsolns.com

Static Data Members � Whenever a object is created a new copy of data

variables is created for that object.

� This means that each objects works on its own copy of data variables.data variables.

� C++ uses another type of variable declaration called as static.

� A data member of class can be qualified as static

� The static member variable has certain special characteristics.


www.sahajsolns.com

Static Data Members� These are:

� It is initialized to zero when the first object of its class is created. No other initialization is permitted.

� Only one copy of that member is created for the entire � Only one copy of that member is created for the entire class and is shared by all the objects of that class, no matter how many objects are created.

� It is visible only within the class, but its lifetime is the entire program.


www.sahajsolns.com

Static Data Members� PROGRAM:CH4PG9.CPP

Note that the type and scope of each static member

int item :: count ;

� Note that the type and scope of each static member variable must be defined outside the class definition.

� This is necessary because the static data members are stored separately rather than as a part of an object.

� Since they are associated with class itself rather than objects, they are known as class variables.


www.sahajsolns.com

Static Data Members

number number number

Object A Object B Object C


count

Common to all three objects

www.sahajsolns.com

Static Member Functions� Like static member variables, C++ has static member

functions.

� A member function that is declared as static has following properties:following properties:� A static function can have access to only other static

members (functions or variables) declared in the same class.

� A static member function can be called using the class name (instead of its object)

� Syntax: class-name::function-name;

� Program: Ch4Pg10.cpp


www.sahajsolns.com

Array of Objects� Arrays can be of any data type including class and

struct.

� Such variables are called array of objects.

� Syntax;� Syntax;

class-name object-name[size];

� Example:

employee manager[20];

� Program :CH4PG11.cpp


www.sahajsolns.com

Objects as function arguments� Like any other data type, an object may be used as a

function argument.

� This can be done in two ways:

� A copy of the entire object is passed to the function.� A copy of the entire object is passed to the function.

� Only address of the object is transferred to the function.

� Program: CH4PG12.cpp


www.sahajsolns.com

Friend Functions� It is possible to grant a non-member function access to

the private members of a class by using a friend.

� A friend function has access to all private and protected members of the class for which it is a friend. protected members of the class for which it is a friend.

� To declare a friend function, include its prototype within the class, preceding it with the keyword friend.

� Syntax:

friend type fn-name(arg-list){

//function body

} Program:CH4PG13.cpp


www.sahajsolns.com

Friend Function� In this example, the sum() function is not a member of

myclass.

� However, it still has full access to its private members.

� Also, notice that sum() is called without the use of the � Also, notice that sum() is called without the use of the dot operator.

� Because it is not a member function, it does not need to be (indeed,it may not be) qualified with an object's name.


www.sahajsolns.com

Friend Function� A friend function possesses certain special

characteristics:� It is not in the scope of the class to which it has been

declared as friend.

� Since it is not in the scope of the class, it cannot be called using the object of that class.

� It can be invoked like normal function without the help of any object.

� It can be declared in public or private part of the class without affecting its meaning.

� Usually its has objects as its arguments.


www.sahajsolns.com

A function friendly to two classes� Program:CH4PG14.cpp

� The function max() has arguments from both XYZ and ABC.

� When the function max() is declared as a friend � When the function max() is declared as a friend function in XYZ for the first time, the compiler will not acknowledge the presence of ABC unless its name is declared in the beginning as

class ABC;

� This is known as forward declaration


www.sahajsolns.com

Friend Classes� It is possible for one class to be a friend of another

class.

� When this is the case, the friend class and all of its member functions have access to the private members member functions have access to the private members defined within the other class.

� For example,

class Y {

friend class X;

};

Program : CH4PG15.cpps


www.sahajsolns.com

Defining Inline Functions Within a

Class� It is possible to define short functions completely

within a class declaration.

� When a function is defined inside a class declaration, it is automatically made into an inline function (if it is automatically made into an inline function (if possible).

� It is not necessary (but not an error) to precede its declaration with the inline keyword.

� Program : CH4PG16.cpp


www.sahajsolns.com

Returning Objects� A Function can not only receive objects as arguments

but also can return them .

� The following program demonstrates this concept.

� Program: CH4PG17.cpp� Program: CH4PG17.cpp


www.sahajsolns.com

Structures and Classes Are Related� A class is syntactically similar to a struct. But the

relationship between a class and a struct is closer thanyou may at first think.

� In C++, the role of the structure was expanded,� In C++, the role of the structure was expanded,making it an alternative way to specify a class.

� In fact, the only difference between a class and a structis that by default all members are public in a struct andprivate in a class.


www.sahajsolns.com

Unions and Classes Are Related� Like a structure, a union may also be used to define a

class.

� In C++, unions may contain both member functionsand variables.and variables.

� They may also include constructor and destructorfunctions.

� A union in C++ retains all of its C-like features, themost important being that all data elements share thesame location in memory.


www.sahajsolns.com

Constructors� A constructor is a special member function whose task is

to initilize the object of its class.

� The constructor is invoked whenever the object of the class is created.

Syntax: Example:� Syntax:

class class-name{

public:

class-name() //constructor

{

}

};


Example:class integer{

int x,y;public:integer(){

x=0;y=0;

}};

www.sahajsolns.com

Constructors� Characteristics of constructors;

� They should be declared in public section.

� They have no return type not even void and therefore they do not return values.they do not return values.

� They cannot be inherited , though derived class constructors can call base class constructor.

� Constructors cannot be virtual.

� Program: CH4PG18.cpp


www.sahajsolns.com

Types of constructors� There are three types of constructors in C++:

� Default Constructors

� Parameterized Constructors

� Copy constructors� Copy constructors

� Default Constructors:

� A default constructor is a constructor which does not accept any arguments.


www.sahajsolns.com

Parameterized Constructors� A constructor which accepts arguments is called as

parameterized constructor.

� Syntax:

class-name :: class-name(argument-list)class-name :: class-name(argument-list)

{

//body of the constructor

}

� Example:


class integer{int x,y;

public:integer(int a, int b){

x=a;y=b

}};

www.sahajsolns.com

Parameterized Constructors� An parameterized constructor can be called using two

ways

� By calling the constructor explicitly

� By calling the constructor implicitly� By calling the constructor implicitly

� Examples:

integer i=integer(10,20); //explicit call

integer i(10,20); //implicit call

Program:CH4PG19.CPP


www.sahajsolns.com

Constructor Overloading� A class can have one or more than one constructors

defined in a class with different number of arguments or different type of arguments.

� This is called constructor overloading.� This is called constructor overloading.

� The compiler recognizes the constructor depending upon the number of arguments or type of arguments.

� Program: CH4PG


www.sahajsolns.com

Copy Constructor� A Constructor which accepts an copy of its own class as

an argument is called an copy constructor.

� Syntax:

class-name:: class-name(class-name &obj)class-name:: class-name(class-name &obj)

{

//constructor body

}

� A copy constructor is used to declare and initialize an object from another object.


www.sahajsolns.com

Dynamic Constructor� The constructor can also be used to allocate memory

while creating objects.

� This ensures the system to allocate the right amount of memory for each object when the objects are not of memory for each object when the objects are not of the same size, thus resulting in the saving of memory.

� Allocation of memory to objects at the time of their construction is known as dynamic constructor.


www.sahajsolns.com

Constructors with Default

Arguments� It is possible to define constructors with default

arguments.

� For example:

Complex( float real, float img=0);Complex( float real, float img=0);

� The argument img=0. Then the statement

� Complex(5.0);

� Assigns 5.0 to real and 0 to img (by default) variables.

� Complex(2.0,3.0);

� Will assign 2.0 to real part and 3.0 to img variables.


www.sahajsolns.com

Sahaj Computer Solutions Near Gomatesh School, Hindwadi Belgaum-11, Phone no: 4200864,2481703

Get Certified in

•Microsoft Office 2010•Tally 9.2•.NET 2008•J2EE•CORE JAVA

� Around 1800 students developed software projects and scored the top scores in exams.

� One stop shop for •CORE JAVA•C PROGRAMMING•OOPS WITH C++•JOOMLA•WORDPRESS•PHP AND MYSQL•SQLSERVER•UNIX AND LINUX•ANDRIOD APPS

� One stop shop for � Software Projects

� Website Development

� Technology Training

� I.T Research Visit: www.sahajsolns.com

OOPS with C++ Sahaj Computer Solutions 40

classes and objects · classes and objects class declaration class members data constructors...

Documents