CPlus Pres 2

8/12/2019 CPlus Pres 2

1/20

1

Features of OOP

Emphasis on data rather thanprocedure.

Programs are divided into objects. Data structures are designed such

that they characterize the objects. Functions that operate on the data of

an object are tied together in the data

structure.

Objects may communicate with eachother through functions.

Data is hidden & can not be accessedby external function.

New data and functions can be easilyadded whenever necessary. Follows bottom up approachin program design.


2/20

2

Concepts used in OOP

Objects

Classes

Data Abstraction

Data Encapsulation

Inheritance

Polymorphism

Dynamic binding

Message Passing


3/20


4/20


5/20

5

Members of a structure can be directlyaccessed anywhere within their scope.

C++ attempts to bring user defined data typesas close as possible, to the built-in

data_types and also provides a facility to

hide the data which is an important concept

of OOP.

Class

It is a data type in C++ which holds dataand functions.

It has two parts:Class declaration

(same as structure declaration)

Class function definition(describes how the functions are

implemented)


6/20

6

General Form of class

class class_name

{

private:

variable_declarations;

function_declarations;

data members member functions

public:

variable_declarations;function_declarations;

}class item

{ private:

int num;

float cost ;public:

getdata(int a, float b);

void putdata(void);

}


7/20

7

Class is usually grouped under twosections Private & Public.

Private members can be accessedonly within the class (data hiding)

and not visible / accessible outside

the class.

oPublic members can be accessedfrom outside the class also.

Only member functions (private/public)can have access to the private members

(data & functions).

Binding of data and functions togetherinto a single class_type variable is called

Encapsulation


8/20

8

General convention for class is to make thevalue part (variable members) of the data typeprivate and make the functions public.

Actual function definitionscan appearwithin the class or outside the class,

anywhere in the program.

Objects can be created by simpleDeclaration such as: itemx, y, z; (itemis a class)

Defining member functions

Inside the class Outside the class

classitem

{int num; float cost; (default private)//declaration// public:void getdata (int a, float b);

void putdata (void);{ cout


9/20

9

Outside the class

return_type class_name :: func_name (arg_list)

{ body }

tells compiler that fu-name belongs to which class

classitem

{ int num; float cost;

public:

void getdata (int a, float b);

//declarations void putdata (void);}

void item :: getdata (int a, float b);

{ num = a;

Can access cost = b;

private data };

(num & cost) void item ::putdata (void);

{ cout


10/20

10

Making an outside functioninline

One of the objectives of OOP is to separate thedetails of implementation from the class definition.

Good practice is to define the memberfunctions outside the class.

We can define such functions as inline by justusing qualifier inline.

When a function is defined inside a class, it istreated as an inline function that means onlysmall functions are defined insides the class.

class item

{ :

public

void getdata (int a, float b);

} ;

inlinevoid item :: getdata (int a, float b)

{ num = a; cost = b; }


11/20

11

Accessing class members

Note that objects communicate by sendingand receiving messages through the member

functions.

itemX;

X . getdata (10,7.5)X . putdata ( ) ;

Objects of the class can call only publicmember functions by using dot operator.

In publicsection, if we define a variableval, then it can be accessed directly outside

in the main program.

X .val + 10;

If valis defined in privatesection, thenabove statement is illegal.


12/20

12

Nesting of member functions Member function can be called by using

its name inside another member function

of the same class.

This is called nesting of member

function.

Private member function Some situations may require to hide

member functions as well.

For examples:

oDeletion of an account in customer file,oProviding increment etc.

classsample

{ int m;

void get (void);

public:void update (void);}


13/20

13

voidsample :: update (void){ get ( ) }private member function

sample S;

S . update ( ) legal

S . get ( ) illegal

Memory Allocation for Object When a class is declared, member functions

are created and placed in the memory space

only once.

But when object is declared as a specific

class type, same member functions are usedand no separate allocation done. But space

for member variables is allocated for each

object.


14/20

14

Static member variables

Used to maintain values common to entireclass.

Type and scope of each static membervariable must be declared in the beginning

of the class definition and defined outside.All objects share same copy of static

variable.

They are associated with class rather thanobject, therefore, called class variables.

They are visible only within the class butits lifetime is the entire program.

It is initialized to zero when the firstobject of its class is created.


15/20

15

class item

{ static int count; int num;

public :void getdata (int a )

{ num = a;count ++;

}

void getcount (void )

{ cout


16/20

16

Static member functions

Static function can have access to staticmembers (functions / variables ) declaredin the same class.

Static member function can be called usingthe class name (instead of its objects)

Static function callitem :: static_fun;

Non static function callitem T;

T. fun_name;

Arrays of objects

item a[10];

a[i] . getdata;a[i] . getcount;


17/20

17

Objects as Arguments in the Function

There are two ways of passing object as aparameter.

call by value call by reference

A copy of the entire Only the address ofobject is passed to the object is transferred

the function to the function

Object can be passed to any function(member functions of the same class or to a

non_member function).

class item

{ int num;public :voidgetdata (int a )

{ num = a; }

voidadd (item S1, item &S2 ){ cout


18/20

18

Returning objects

Functions can return objects.

classcomplex

{ private:

floatx; floaty;

public :

void inputdata (float r , float i)

{ x = r ; y = i ; }void show(complex c)

{ cout


19/20

19

Constant Member Function

If member function does not alter any datain the class, we may declare it as constmember function by appending a function

declaration with the qualifier const.

voidmult (int, int) const ;

Error message is generated if such functiontries to alter the data.

Pointers to Members

Address of a member (data / function) canbe obtained by applying &operator to a fullyqualified class member name.

A class using pointer can be declared usingthe operator ::*with the class name.


20/20

20

classitem

{ int m;

public :

voidshow ( ) ;

}

Pointer to the members of a class itemis defined by item ::*

Example: Pointer ptrto member mis defined as

int item :: *ptr = &item :: m;

int *ptr = & m Invalid

Here &item :: m means address of m.(m is a member of class item) ptr defined above can be used to access

the member minside the member functions

and not outside the class.

itema; // inside a member function

cout

CPlus Pres 2

Documents

Transcript of CPlus Pres 2