object oriented programming with c++

OBJECT ORIENTED OBJECT ORIENTED PROGRAMMING WITH C+PROGRAMMING WITH C+++

OBJECT ORIENTED OBJECT ORIENTED PROGRAMMING WITH C+PROGRAMMING WITH C+++

B.R.MOHAN

CSE DEPT

SSE, MUKKA

Prof. B.R.Mohan, SSE--> www.bookspar.com | Website for students | VTU NOTES

Text Book 1. Object oriented Programming with C++, Sourav Sahay, Oxford Press, 2006 (chapters1-10)

Reference Books1. C++ Primer, Stanley Lipmann, Josee Lajoie, Barbara E. Moo, 4th Edition, Addison Wesley, 2005

2. The Complete Reference C++, Herbert Schildt, 4th Edition, TMH, 2005


Unit-1: 1. Introduction to C++2. Class and Object

Unit-2:

3. Class & Objects contd.

Unit-3:

4. Dynamic Memory Management

5. Constructors and Destructors


Unit-4:6. Inheritance

Unit-5:7. Virtual Functions & Dynamic Polymorphism

8. Stream HandlingUnit-69. Stream Handling contd 10. Operator

Overloading


Unit-7:11. Operator Overloading contd. Unit-8:

12. Type Conversion, New style

casts, and RTTI

13. Templates FT,CT, STL

14. Exception Handling


Here we see how to program in C++ - a language that support object oriented programming. Reference – Robert Lafore

Key concepts in OOPs – Objects and Classes

Oops came into existence due to the limitations

discovered in procedural languages.


Procedural Languages –

Pascal, C, Basic, Fortran are examples of procedural languages.

lays emphasis on executing a set of instructions.

-Get some input

-Add these numbers

-divide by 6

-display the results


• A program in procedural language is a list

of instructions.For small programs, no other organizing principle is needed.

• As program grows larger, it becomes difficult to comprehend.

Hence Divide the large program into a number of functions.

A Function has a clearly defined purpose and a well defined interface.


1. Dividing a function into a number of functions can be extended to grouping a number of functions into a larger entity called Module.

2. Dividing a program into functions andmodules is one of the cornerstone of Structured Programming( other features include loops and other control structures).

3. As program grow even larger , structured programming signs of strain.


Drawbacks/Disadvantages of Procedural languages.

1. Data is undervalued – given II class status in program organization of procedural languages.

2. Since many functions in a program can access global data / global variables, global data can be corrupted by that have no business to change it.

Global variables constitute data are declared outside any function so that they are accessible to all functions


Since many functions access the same data,

the way data is arranged becomes critical.

• Data arrangement cannot be changed without modifying the functions that access it. If u add new data items , we need to modify all the functions that access the data so that they can also access these new items


Function A

Local Var Local Var

Function B

Global Variable Accessible by any function

Accessible by Function A

Accessible by Function B


Fn A Fn A Fn A Fn A

GlobalData Global Data Global Data Global Data


Hence we need a way to restrict the access to the data , to hide it from all but a few critical functions. This protects the data, simplifies the maintainence and other benefits.

Object Oriented Approach

Idea of Object Oriented Language – data and the functions that access the data are combined into a single unit called OBJECT.

An objects functions are called Member functions in C++.

MFs provide only way to access data.


How to read a data item in an object ?

• Call the mf of the object and it will read the data item and return the value to u.

• Data cant be accessed directly, it is hidden within the object and safe from accidental alterations.

• Data and functions are said to be encapsulated in an object.

• Data Encapsulation & Data Hiding are the key terms in OOPs


• OOPs simplify writing , debugging and maintaining the program.

• C++ prg typically contain a number of objects interacting with each other by calling one another’s member functions.


Organization Of a C++ Program

Fig – Object Oriented Paradigm

object

MF

MF

Data

MF

MF

Data

MF

MF

Data

Object Object


Corporate Paradigm

Finance Dept

CSE Dept

Personnel Dept

Sales Data

Personnel Manager

Secretary

Personnel Data

Personnel Staff

Finance Data

Finance Manager

Financial Assistant

Sales Manager


There is a close match between programming sense & objects in real world

Classes – Objects are instances / members of

a class.

Eg- All programming languages have built in

data types like int, char, float,etc.

Similarly u can have objects of same class as

shown


A Class serves as a plan / template like structure, specifies what data & functions will be included in objects of the class. Fig- A Class & its Objects

Object1 Object2 Object3

Class CircleFeature A Feature B

Feature CSpecifications for class

Circle


Feature C


Feature C


Feature C


Object1, Object2 and Object3 are all objects of a Class Circle that are similar to i, j, k are of integer data type in C language.

Saimple programs are given in VC++ D:\


C++ Program execution

Execution starts from main( ).

smallobj s1,s2;

Defines 2 objects s1,s2, of class smallobj.

Class smallobj doesn’t create any objects , but

describes how they look when they are created.

Space is set aside for it in memory.

S1.setdata(1066) ; //causes somedata set to 1066

. -> class member acess operator connects object name and member function


C++ introduces a new keyword class as a substitute for keyword struct .

structure members are public by

default


Struct Distance

{

private:

int iFeet;

float fInches;

Public:

void setFeet(int x)

{

iFeet=x;

}

float getFeet()

{

return iFeet;

}

int setInches(float y)

{

fInches = y;

}

float getInches()

{ return fInches;

}

}; This can also be written as given in next slide


Struct Distance

{

private:

int iFeet;

float fInches;

void setFeet(int x) //All member functions are public by default

{

iFeet=x;

}

float getFeet()

{

return iFeet;

}


{

fInches = y;

}

float getInches()

{ return fInches;

}

};


class members are private by

default


class Distance

{

Private:

int iFeet;

float fInches;

Public:

void setFeet(int x)

{

iFeet=x;

}

float getFeet()

{

return iFeet;

}


{

fInches = y;

}

float getInches()

{ return fInches;

}

}; class members are private by default


class Distance

{

int iFeet; //private by default

float fInches; //private by default

Public:

void setFeet(int x)

{

iFeet=x;

}

float getFeet()

{

return iFeet;

}


{

fInches = y;

}

float getInches()

{ return fInches;

}

};


Classes and ObjectsClasses contain Data and Functions

Class

DataFunction

Data1Data2Data3

Fn1Fn2Fn3


Class can contain private and public.Usually the data within the class is private and the functions that operate on data are public so that they can be accessed from outside the class. Fig- for public & private

Not accessible

From outside

Class

Accessible from

Outside class public

Data or Functions

Data or Functions

private

Class


Syntax of a Class SpecifierClass Circle name of class

{ class is a keyword

private:

int data; private functions & data

public:

void DisplayRadius( );

void CalcArea( ); public functions & data

void CalcCircum( );

};


Differences between C and C++

In C, u may / may not In C++, you must

Include function include function

Prototypes prototypes. C++ lets

you

specify default

values for function‘s

parameters


C++ lets you

specify default

values for function‘s parameters in the

function’s protoype


Eg-void myfunction(int x=3,int y=4)In C, the declaration In C++, u may

Of a variable must place the be at the beginning variable declaraOf the function tions close to

the statementsthat use variables beforeusing it in astatement


If a C program uses a In C++, u can

Local variable that has instruct prgm

Same name as global to use value of

Variable, then C program global variable

uses the value of a with scope

local variable. Resolution operator

Eg-

cout << “Iam

global var :

” << ::I;


Lab Program-1

1. Given that Employee class contains following

members: employeeno., empname, basic , da, it,Netsalary and to print data members.Write a C++ program to read the data of nemployees and compute netsalary of eachemployee.(da=52%of basic and it =30% of grosssalary, netsalary=basic+da-it)


• Steps :1. Define an Employee class and declare the given data members.2. Get the employee details using the member function3. calculate netsalary of given employee using formula

display the resultant value4. write the main function and create Employee objects. Call

member functions on the employee objects to read the data ,to calculate netsalary and to print the data membersClass:

• The class is a fundamental OOP concept in C++. • A class declaration defines a new type that links

code(functions/operations) and data.• This new type is then used to declare objects of that class.


• The class is a fundamental OOP concept in C++. • A class declaration defines a new type that links

code(functions/operations) and data.• This new type is then used to declare objects of

that class. Hence , a class is a logical abstraction, but a physical existence.


Syntax:

class name objectname

object name.datamember; //access class members

object name.datamember; //calling mf on an object

Access specifiers:

public: allows fns / data to be accessible to other parts of ur

Prg

private: by default fucntions and data declared within a class

are private to that class and may be accessed only by public

members of the same class.


Class definition follows

Class Employee{

//declare data members here

int empno;

char empname[25];

float basic, da, it, netsal;

public:

void getdata();

void computenetsal(); void display();

};


Member functions

void employee::getdata() { //get emp details}

void employee::computenetsal() {

da=0.52*basic;

gross=basic-da;

it=0.3*gross;

//compute netsal

netsal=basic+da-it;

}


Void employee::display()

{

//display employee info on the monitor

}


2. Define a student class with Usn, name , marks in

3 tests of a subject. Declare an array of 10 student objects. Using appropriate functions, find average of 2 better marks for each student. Print usn, name and average marks of all students.


Steps For II Programs

1. Define a Student class and declare the given members.

2. Get the Student details using member functions to get data

3. Find the average of 2 better marks for each student4. Display resultant values – usn, name and average

marks of all students


5. Write main() function and create an array of 10 student objects. Call member functions on student objects to read data to calculate average marks and to print the student details along with average marks.


Steps-

1. Define a student class and declare the given data

members

2. Get the student details using member function- getdata()

3. Find average of 2 better marks for each student

4. Display the resultant values-usn, name and average marks of all students

5. Write a main() & create an array of 10 student objects. Call mfs of student objects to read data,

to calculate average marks & print the

student details along with their avg mks


Lab Program-3

• Write a C++ program to create a class called COMPLEX and implement following overloading functions ADD that return a COMPLEX number.

i) ADD(a,s2) - where a is an integer (real part)

and s2 is a complex number.

ii) ADD(s1,s2) – where s1, s2 are complex

numbers


Steps for LAB PRG III

Constructor :

1. Create a user defined datatype named as COMPLEX. Declare the data members.

2. Initialize data members with default values. This is a default constructor automatically invoked when an object of type COMPLEX is defined / created.


3. Or initialize the data members with default values specified while creating the object. This is a Parameterized constructor, automatically invoked when some initial values are passed as parameters while creating an object.

4. Add an integer with a COMPLEX value5. Add 2 COMPLEX objects overloading the ADD

function


6. Display the results directly or by overloading << operator

7. Write a main() function and call member functions on the COMPLEX objects as required by the end user.


Friend Function

If u want to explicitly grant access to a function that is not a member of current class, declare that function a friend inside the class / structure declaration.

Friend declaration occurs inside the class because compiler reads class definition, size and behaviour of data type


• Who can access my private implementation ?

Only friend functions can access private

Implementations

U cant break in from outside if u are not a friend.

Hence the operator << is overloaded to print the

complex number.


It is possible to grant nonmember function access to the private members of a class by using a friend.

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

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

Friend FunctionsProf. B.R.Mohan, SSE--> www.bookspar.com | Website

for students | VTU NOTES

OBJECT ORIENTED PROGRAMMING WITH C++

REVIEW OF STRUCTURES


To understand procedural oriented languages, we need to review structure concept

Need for Structures – value of 1 variable depends on the value of another variable.

Eg- Date can be programmatically represented in C by 3 different int variables.

Say int d,m,y; d-date, m-month, y-year


Although 3 variables are not grouped in a code, they actually belong to the same group. The value of 1 may influence the value of other. Consider a function nextday( ) that accepts the addresses of 3 integers that represent a date and changes these values to represent next day


Prototype of this function//for calculating the next dayvoid nextday(int *,int *);

Suppose

d=1;

m=1;

y=2002; //1st january 2002

If we call nextday( &d, &m, &y);

D becomes 2, m=1,y=2002


But if d=28;m=2;

y=1999;//28th Feb 1999

and we call the function as

nextday( &d, &m, &y);

d becomes 1, m will become 3 and y will become 1999.


Again if d=31;m=12;

y=1999;//31th Dec 1999

and we call the function as

nextday( &d, &m, &y);

d will become 1 , m will become 1 and y

becomes 2000.

A change in 1 variable may change the value of other 2.

No language construct exist that actually places them in same group.


Members of wrong group may be accidentally sent to the function

d1=28; m1=2; y1=1999; //28thfeb99

d2=19; m2=3; y2=1999; //19thmrch99

nextday(&d1,&m1,&y1); //ok

nextday(&d1,&m2,&y2); //incorrect set passed

Above listing show problems in passing groups of programmatically independent

but logically dependent variables


There is nothing in language itself that prevents the wrong set of variables from being sent to the function. Suppose nextday() accepts an array as parameter,

Then its prototype will be

void nextday(int *);

Let us declare date as an array of 3 integers.

int date[3];

date[0]=28;

date[1]=2

date[2]=1999; //28th Feb 1999


Let us call the function as followsnextday(date);

The values of date[0],date[1],date[2] is set to 1,3 and 1999, respectively.

This method is not convincing. There is no data type of date itself.

The solution to this problem is to create a datatype called date itself using structures.


Struct date d1;d1.d=28;d1.m=2; //Need for structuresd1.y=1999;nextday(&d1);

d1.d, d1.m, d1.y will be set correctly to 1,3,1999, since the function takes the address of an entire structure variable as parameter at a time as there is no chance of variables of different groups being sent to the function.

Structure is a programming construct in C that allows us to put the variables together


Library programmers use structures to create new datatypes. Application programs use these new datatypes by declaring variables of this data type

struct date d1;

They call associated functions by passing these variables / addresses to them.

d1.d=31;

d1.m=12;

d1.y=2003;

Nextday(&d1);


They use resultant value of the passed variable further as per requirement

printf(“The next day is: %d /%d/%d\n”,d1.d,d1.m,d1.y);

O/P- The next day is:01/01/2004


Creating a New Data Type using Structures

Creation of a new datatype is a 3 step process.

1. Put structure definition and prototypes of associated functions in a header file.

2. Put the definition of associated functions in a source code and create a library.


3. Provide the header file and library in any media to other programmers who want to use this new data type. Creating a structure and its associated functions are 2 steps to constitute one complete process


1. Putting structure definition and prototypes of associated functions in a header file.

//date.h contains structure definition &

// prototypes of associated functions

Struct date

{

int d, m, y;

}

Void nextday(struct date *);

Void getsysdate(struct date *);


2. put definition and other prototypes in a source code and create a library

#include “date.h”

Void nextday(struct date *p)

{//calculate date represented by *p and set it to *p}

Void getsysdate(struct date *p){ // determine //current system date & set it to *p}

//definitions of other useful & other relevant

//functions to work upon vars of date structure


Using Structures in Application Programs is a 3 step procedure

1. Include header file provided by programmer in the source code.

2. Declare variables of new data type in the source code

3. Embed calls to the associated functions by passing these variables in the source code


4. Compile the Source code to get the object file.

5. Link the Object file with the library provided by the library programmer to get the executable or another library.


Step1-Include the header file provided by the programmer in the source code

//beginning of dateuser.c


void main()

{

…

…

} //end of dateuser.c


2. Declare variables of new data type in the source code.

//beginning of dateuser.c


void main()

{ struct date d;

…

…

} //end of dateuser.c


3. Embed calls to associated functions by passing these variables in source code

//beginning of dateuser.c#include “date.h”void main(){ struct date d;d.d=28; d.m=2; d.y=1999;nextday(&d);…} //end of dateuser.c


Procedure Oriented System has the following programming pattern -

1. Divides code into functions. 2. Data (contained in structure variables) is

passed from 1 function to another to be read from or written into.

3. Focus is on Procedures / functions.4. Procedures / functions are dissociated from

data & are not a part of it. Instead receive structure variables / their addresses & work upon them


Drawback/Disadvantage1. Data is not secure and can be manipulated by

any function/procedure.2. Associated functions that were designed by

library programmer don’t have rights to work upon the data.

3. They are not a part of structure definition itself because application program might modify

the structure variables by some code inadvertently written in application program itself


Consider an application of around 25,000 lines in which the variables of structure is used quite extensively. 1. Testing may find that date being represented

by one of these variables has become 29th Feb 1999.

2. This faulty piece of code can be anywhere in the program.

3. Hence Debugging will involve a visual inspection of the entire code & will not be limited to associated functions only.


4. While distributing his/her application, application programmer cant be sure that program would run successfully.

5. Every new piece of code accessing structure variable will have to be inspected and tested again to ensure that it doesn’t corrupt the members of structure.

6. Compilers that implement procedure oriented programming systems don’t prevent unauthorized functions from accessing / manipulating the structure variables.


7. To ensure a successful compilation of his/her code, application programmer is forced to remove those statements that access data members of structure variables.

8. Lack of data security of procedure oriented programs has led to Object Oriented Programming Systems


Object Oriented Programming Systems

• Model real-world objects• RWO has internal parts & interfaces that enable us to operate them.

Eg-LCD is RWO-has a fan and a lamp.There are 2 switches 1 to operate fan & other to operate lamp.

Switch operation has rules.If lamp is switched on, fan is automatically switched on, else lcd will be damaged.


• Lamp is also switched off if fan is switched off and switches are linked with each other.

Common Characteristic of RWO- • If a perfect interface is required to work on an object , it will have exclusive rights to do so.

• Coming to C++, observed behaviour of LCD projector resembles the desired behaviour of the date’s structure variables.


• Compilers implementing OOPs enable data security enforcing a prohibition by throwing compile-time errors against the pieces of code.

• RWO ensure a guaranteed initialization of objects

OOPS Features –

1. Inheritance 2. Polymorphism


Inheritance allows one structure to inherit the

Characteristics of other structure.

variable of new structure will contain data

members mentioned in new structure definition.

Due to inheritance, it will also contain data

members in existing definition from which new

structure has inherited.


In Inheritance, both data and functions may be inherited

• Parent class can be given the general characteristics, while its child may be given more specific characteristics.

• Inheritance allows code reusability by keeping code in a common place – the base structure.

• Inheritance allows code extensibility by allowing creation of new structures that are suited to our requirements compared to existing structures.


Inheritance – a process by which 1 object can acquire the properties of another object.This is important as it supports classification

Most knowledge is made of hierarchicalClassification.Eg-Red delicious apple is part of apple classification which in turn is a part of fruit class, which is under the larger class food.

Inheritance mechanism makes it possible for one object to be a specific instance of a more general class.


Polymorphism

Using operators or functions in different ways

depending on what they are operating on is

called Polymorphism

Static & Dynamic Polymorphism

Function overloading & OperatorOverloading


Function Prototyping

• FP is necessary in C++. • C++ strongly supports function prototypes• Prototype describes the function’s interface to the

compiler• Tells the compiler the return type of function, number ,

type and sequence of its formal arguments


GENERAL SYNTAX OF FUNCTION PROTOTYPEreturn_type function_name( argument_list);

Eg-

int add ( int, int);

indicates add() function returns a int type and takes

2 arguments both of int type and terminates with ;


With prototyping , compiler ensures following

1. The return value of a function is handled correctly.

2. Correct number and type of arguments are passed to a function.


Since C++ compiler require function

prototyping, it will report error against function call

because no function prototype is provided to resolve

the function call.

Compiler may still give an error, if function call

doesn’t match the prototype.

Hence prototyping guarantees protection from

errors arising out of incorrect function calls


Sometimes function prototype & function call may not match

FD and FP are both created by Libraryprogrammer.

He/She puts FP in a header file , puts FD in alibrary.

Application programmer includes header filein his/her application program file in which functionis called.

He creates an object file from application file and links this object file to the library to get an executable file.


Function Prototyping produces automatic type of conversion. Wherever appropriate


Objects – Variables of classes are known as Objects

SCOPE RESOLUTION OPERATOR (SRO) –

It is possible and necessary for Library programmer to define member functions outside their respective classes.

SRO makes this possible. Example illustrates the use of scope resolution operator


class Distance

{

int iFeet;

float fInches;

public:

void setFeet(int); //only member function

int getFeet(); //prototypes are given

void setInches(); //in the class definition.

float getInches();

};


Member Functions are prototyped within the class and have been defined outsidevoid Distance :: setFeet (int x) //definition

{

iFeet=x;

}

int Distance :: getFeet() //definition

{return iFeet;

}


void Distance :: setInches (int y) //definition{

fInches=y;}

int Distance :: getInches() //definition{

return fInches;} code showing use of scope resolution operator

that specifies class to which member function belong. The class name is specified on LHS of SRO and name of member function being defined is on the right hand side


Creating Libraries using the Scope Resolution Operator

Creating a New Data type

/ class is also a 3 step Process

i.e. executed by the

Programmer.


Step-1. Place the class definition in a header file.

Step-2. Place the definitions of member functions in a C++ source file / library source

code / class implementation file. Step-3. Provide header file and library file in any media to other programmers who want to use this new datatype.


Step-1. Place the class definition in a header file.

//Distance.h- header file containing Distance class

class Distance

{

int iFeet;

float fInches;

public:

void setFeet(int); //only member function

int getFeet(); //prototypes are given

void setInches(); //in the class definition.

float getInches();

};


Step-2. Place the definitions of member functions in a C++ source file / library source code / class implementation file

//implementation file for class Distance –

//Distlib.cpp


void Distance :: setFeet (int x)//definition

{

iFeet=x;

}

int Distance :: getFeet() //definition

{ return iFeet;

}


Void Distance:: setInches (int y) //definition{

iFeet=x;}int Distance::getInches() //definition{

return fInches;


Step-3. Provide header file and library file in any media to other programmers who want to use this new datatype.


Using classes in theApplication Programs

The five steps followed by Programmers for using this new datatype / class are –


Step-1. Include the header file provided by the programmer in their source code//distmain.cpp

#include “Distance.h”

void main()

{ ….

….

} //end of Distmain.cpp


Step-2. Declare variables of the new datatype in their source code//Distmain.cpp#include “Distance.h”void main(){Distance d1,d2;……} //end of Distmain.cpp


Step-3 Embed calls to the associated functions by passing these variables in their source code

Listing in next slide shows how to use

classes in the application programs


//distmain.cpp- A sample driver program for creating and using objects of class Distance

#include<iostream.h>

#include “Distance.h”

void main()

{Distance d1,d2;

d1.setFeet(2); d2.setInches(2.2);

d1.setFeet(3); d2.setInches(3.3);

cout << d1.getFeet() << “ “ << d1.getInches();

cout << d1.getFeet() << “ “ << d2.getInches(); }

}


Step-4 Compile the source code to get the

the object file.

Step-5 Link the object file with the library

provided by the library programmer to

get the executable or any library.

Output – 2 2.2

3 3.3

Implementation files are compiled and

converted into static and dynamic libraries


The ‘this’ pointer-The facility to create and call member functions of class objects is provided bythe compiler. Compiler does this by using a unique pointer -> this

this pointer - always a constant pointer.

- points at the object with respect to which the

function was called


Working of this pointer-Once the compiler is sure that no attempt

is made to access the private members of

an object by nonmember functions, it

converts C++ code into an ordinary code as

Follows.


1. It converts class into structure with onlydata members as followsBeforeclass Distance

{int iFeet;float fInches;

public:void setFeet(int); //only member functionint getFeet(); //prototypes are givenvoid setInches(); //in the class definition.float getInches();

};


After

Struct Distance

{

int iFeet;

float fInches;

};


2. It puts a declaration of the this pointer as a leading formal argument in the prototypes of all member functions as follows

Before –

void setFeet(int);

After -

void setFeet( Distance * const int);


Before –void getFeet()After –void getFeet(Distance * const );

Before –

void setInches( float);

After –

void setInches(Distance * const, float);

Before –

float getInches();

After –

float getInches(Distance * const);


3. It puts the definition of this pointer as a leading formal argument in the definitions of all member functions as follows

It also modifies all statements to access object members by accessing through the this pointer using the pointer-to-member access operator (->).


Before –

void Distance :: setFeet ( int x)

{iFeet = x;

}

After –

void setFeet( Distance * const this, int x)

{

this -> iFeet = x;

}


Before –

int Distance :: getFeet(){ return iFeet; }

After –

int getFeet( Distance * const this){ return this -> iFeet; }


Before – void Distance :: setInches (float y){ fInches = y; }After –Void setInches(Distance * const this, float y){this -> fInches = y;

}


Before –

float Distance :: getInches ()

{ return fInches; }

After –

void getInches(Distance * const this)

{

return this -> fInches;

}


SRO - operates on its operands. - binary operator taking 2

operands. • Operand on its left is the name of a predefined class. Right is a

member function of the class.• Based on this info, SRO inserts a constant operator of correct type

as a leading formal argument to function on its right.


4. Passes the address of invoking object as leading parameter to each call to the member function as follows

Before –

D1.setFeet(1);

After -

setFeet(&d1, 1);

Before –

d1.setInches(1.1);

After –

setInches(&d1 , 1.1);


Before –

cout << d1.getFeet() << endl;

After –

cout << getFeet(&d1) << endl;

Before –

cout << d1.getInches() << endl;

After –

cout << getInches(&d1) << endl;

In case of C++, dot operator’s definition is extended


Its evident that ‘this’ pointer should

continue to point at same object

– the object with respect to which the member Function has been called

– throughout the lifetime.

Hence the compiler creates it as a

constant pointer.


The accessibility of the implicit object is similar to the other objects passed as parameters in function calland local objects inside that function

A new function – add() has been added to

the existing definition of the class


class Distance //Distance.hclass Distance //Distance.h

{{

int iFeet;int iFeet;

float fInches;float fInches;

public:public:

void setFeet(int);void setFeet(int); //only member function//only member function

int getFeet();int getFeet(); //prototypes are given//prototypes are given

void setInches();void setInches(); //in the class definition.//in the class definition.

float getInches();float getInches();

Distance add( Distance);Distance add( Distance);

};};


Distance add( Distance dd)Distance add( Distance dd)

{{ Distance temp;Distance temp;

temp.iFeet = iFeet+dd.iFeet;temp.iFeet = iFeet+dd.iFeet;

temp.fInches=fInches+ dd.fInches;temp.fInches=fInches+ dd.fInches;

return fInches;return fInches;

}}

described conversion for this add() using this ptrdescribed conversion for this add() using this ptr

Distance add( Distance * const this dd)Distance add( Distance * const this dd)

{{ Distance temp;Distance temp;

temp.iFeet = this->iFeet+dd.iFeet;temp.iFeet = this->iFeet+dd.iFeet;

temp.fInches=this->fInches+ dd.fInches;temp.fInches=this->fInches+ dd.fInches;

return fInches;return fInches;

}}

A statement d3=d1.add(d2) is invoked as A statement d3=d1.add(d2) is invoked as


iFeet

fInches

iFeet

fInches

iFeet

fInches

temp

d2d1

d3=d1.add(d2);

Data in temp is assigned to d3 using temp in add(d2) function

Temp.iFeet

Temp.fInches

Similarly d1.iFeet, d1.fInches. D2.fInches, d2.iFeet can be accessed


Explicit Address Manipulation

An Application Programmer can manipulate the

member data of any object by explicit address

manipulation. Like Dot ,arrow operator is also extended

in C++. Arrow operator takes data members and

member functions as its right hand side operand.

A statement

dptr -> setFeet(1); after conversion becomes

setFeet ( dptr, 1);

The value of dptr is copied into ‘this’ pointer.

Hence this pointer also points at the same object at which dptr points //d01.cpp,d11.cpp


Calling 1 member function from another1 member function can be called from another. The

call to the A :: setxindirect() function changes from

A1.setxindirect(1); //c++ call

To

setxindirect(&A1,1); //c call


Function Definition of A :: setxindirect() function changes from

void A :: setxindirect( int q)

{

setx(q);

} to

void A :: setxindirect( A * const this, int q)

{

this -> setx(q); //calling function through pointer

}

that changes to


void A :: setxindirect( A * const this, int q)

{

setx(this,q); //action of arrow operator

}


Member Functions and Member Data

We see different types of member data &

member functions that classes in C++ have

Member functions can be overloaded just like

nonmember functions.

Code d14.cpp illustrates the point.


Function Overloading enables us to have 2 functions of same name and same signature in 2 different classes illustrated below.

Class A

{

Public:

void show();

};

Class B

{

Public:

void show();

};


Knowledge of this pointer tell the signatures of show() are different

Function prototypes in respective classes are

void show(A* const);

void show(B* const);


Default Values for Formal Arguments of Member Functions

Default values can be assigned to arguments of

non-member functions and member functions.

Member functions should be overloaded with care. If

default values are specified for some or all of its

arguments. D15.cpp

For example- Compiler will report an ambiguity error

when it finds the second prototype for the function for

show() of class A as follows. Class A

{ public:

void show();

void show(int =0);

}; //d17.cpp


Reasons for Ambiguity

In case of nonmember functions, if default values are specified for more than 1 formal argument, they must be specified from right to left.

Default values must be specified in the function prototypes, not in function definitions. Further default values can be specified for formal arguments of any type.


Inline Member Functions Member functions are made inline by 2

Methods.1. By defining function within the class

itself. 2. By only prototyping and not defining the function within the class. The function is defined outside the class using Scope Resolution Operator. The definition is prefixed by inline

keyword. As in noninline member functions, the definition of inline function must appear before the function is called.

Hence the function should be defined in the same header file in which the class is defined.


Class Distance

{ int iFeet, fInches; //private by default

Public:

void setFeet(int x)

{ iFeet =x; }

int getFeet() { return iFeet; }

Void setInches(float y) { return fInches; }

float getInches() { return fInches; }

};


//meminline.cppClass A

{

public:

void show();

};

Inline void A :: show() //definition in header file

{

//definition of A :: show() function

}

Inline member Functions


Constant Member Functions

The Library Programmer may desire that one of member functions

of his/her class shouldn’t be able to change the value of member

Data.

Function should merely read values contained in the data

Members, but not change them even accidentally while defining the

function.

Compiler’s help may be sought by declaring function as constant

Function & attempting to change data value through member

Function, the compiler may throw an error.

getFeet() & getInches() and add() of Distance class should obviously

be constant functions and shouldn’t change the iFeet / fInches

members of invoking object even by accident.

Member functions are specified as constants by suffixing prototype

And function definition header with const keyword.

Modified Distance class is written as


Class Distance

{ int iFeet; float fInches;

public:

void setFeet(int);

int getFeet() const; //constant function

void setInches(float);

float getInches() const; //constant function

Distance add(Distance) const; //constant function

};


void Distance::setFeet(int x)

{ iFeet=x; }

void Distance::getFeet() const //const function

{ iFeet++; //ERROR!!

return iFeet; }

void Distance::setInches(float y)

{ fInches=y; }

void Distance::getInches() const //const function

{ fInches=0.0; //ERROR!!

return fInches;

}


void Distance::add(Distance dd) const //const function

{

Distance temp;

temp.iFeet= iFeet + dd. iFeet;

temp.setInches (fInches + dd.fInches);

iFeet++; //ERROR!!

return temp;

}

For const. member functions, memory occupied by invoking

object is a read-only memory. Only const. member functions can

be called with respect to constant objects.

However nonconstant functions can be called with respect to

nonconstant objects.


Mutable Data Members

Mutable data member is never constant.

1. It can be modified inside constant functions also.

2. Prefixing the declaration of a data member with the key word mutable makes it mutable. Code shows in next slide


Class A //mutable.h{

int x; mutable int y;

public:void abc() const //a constant member function{ //error: cant modify a non-constant da

x++; //ta member in a const. mfy++;//ok can modify a mutable data member in

} // const. mfvoid def() //non-const. mf{ x++; //ok can modify nonconstant data

member //in a non-const. mf

y++; //ok can modify mutable data member in a

//nonconst.mf } };/*end of mutable.h*/


We frequently need a data member that can be

modified even for constant objects.

Suppose there is a member function that saves the data of

an invoking object in a disk file. This function should be

declared as a constant to prevent even an inadvertent change

to the data members of the invoking object.

If we need to maintain a flag inside each object that tells

whether the object has already saved or not, such data should

be modified within above constant member function.

Hence this data member should be declared a mutable

member.


Friends- A class can be global non-member function and member functions of other classes as friends.

Such functions can directly access private data members of objects of class.

Friend Non-member functions

a Friend function is a non-member function that has

special rights to access private data members of any

object of class of whom it is a friend.

Here we study only those friend functions that are

not member functions of some other class.


Friend function is prototyped within the definition of

Class of which it is intended to be friend.

It is prefixed with the keyword friend.

Since it is a non-member function, it is defined without

using scope resolution operator. It is not called with respect to an object.


Friend Functions

• Friend keyword should appear in the prototype only and

not in the definition• Since it is a nonmember function of the class of which it

is a friend, it can be prototyped in either private or public

section of the class.• A friend function takes 1 extra parameter compared to a

member function that perform a same task• No need of using scope resolution operator for defining a

member function.


• Friend functions don’t contradict the principles of

OOPs.

• The benefits provided by data hiding are not compromised by friend functions.


Friend Classes• A class can be friend of another class. Member

Functions of a friend class can access private data

members of objects of class of which it is a friend.

If class B is made a friend of class A, example illustrates this

Class A

{friend class B; //declaring class B as a friend of class A

/* rest of class A*/ //doesn’t matter to declare in priv or //public section for friend function

};

fig- declaring friend classes


Member functions of class B can access private members of objects of class A

Listing the effect declaring a friend class frie

Class B; // forward declaration needed because //definition of class B is after stmt declaring

//class B is a friend of class A

Class A

{int x;

Public:

void setx(const int =0);

void getx() const;

friend class B; //declaring class B as a friend of A

};


Class B

{ A * Aptr;

Public:

void Map(const A * const);void test_friend( const int);

};

void B :: Map(const A*, const p);

{

Aptr=p;

}


Void B :: test_friend(int i)

{

Aptr -> x=i; //accessing private data member

}

Code effect of declaring a friend class


• Member functions of class B are able to access private data member of objects of class A although they are not member functions of class A. This is because they are member functions of class B i.e. a friend of class A.

• Friendship is not transitive.• Consider the listing in next slide


Class B; //friendtran.cpp

Class C;

Class A

{

friend class B;

int a;

};

Class B

{

friend class C;

};


Class C

{

void f( A *p)

{

p->a++; //error: C is not a friend of A despite

// being a friend of friend

}

};

//end of friendtran.cpp

Code to show that friendship is not transitive


Friend Member Functions

Can we make specific member functions of 1 class

friendly to another class ?

For making only ‘ B:: test_friend() ’ function a friend

of class A, replace the line

Friend void B::test_friend();

The modified definition of class A is given in next slide


Class A

{

/*rest of class A

Friend void B :: test_friend();

};

To compile this code successfully, compiler should first see definition of class B, else it doesn’t know that test_friend() is a member function of class B.

However, a pointer of type A * is a private member of class B.

This problem of circular dependence is solved by forward declaration by inserting a line

Class A; //Declaration ,only not definition!!

before definition of class B. declarations and

definitions of 2 classes appear in next slide.


//Friendmemfunc.h

class A;

class B

{

A *Aptr;

Public:

void Map(const A * const);

void test_friend(const int=0);

};

class A

{

int x;

public:

friend void B :: test_friend ( const int=0)

};

Forward declaring a class that requires a friend.


Class A;

Class B

{

A *Aptr;

public:

void map(const A *A);

void test_friend(const int =0);

};

Class A

{int x;

Public: friend void B:: test_friend(const int =0);

}; inline void B:: test_friend( const p)

{

Aptr->x=p;

}


Static Data Members – hold global data i.e. common to all objects

Examples of such global data are –

1. Count of Objects currently present

2. Common data accessed by all objects, etc.


Consider class Account and we may Want all objects to calculate interest rate

at 4.5%.

Hence this data should be available

globally to all objects of this class.

This data should be stored globally to

All objects of this class.


Objects and Functions – Objects appear as local variables. They can also be passed by reference to

Functions.

Finally they can be returned by value or by reference from the functions.

Distloc.cpp, distarray.cpp largedist.cpp


Arrays Inside Objects – An array can be declared inside theclass. Such an array becomes a member all objects of class. It can beaccessed / manipulated by all member functions of the class.

#define SIZE 3

/*A class to duplicate the behavior of an integer array*/

class A

{

int iArray[SIZE];

Public:

void setElement (unsigned int,int);

int getElement (unsigned int);

};


/*function to write the value passed as a second parameter

At position passed as first parameter*/

void A::setElement(unsigned int, int)

{ if (p<=SIZE) return; //better to throw an exception

iArray[p]=v;

}

/*function to read the value from the position passed as parameter*/

int A::getElement(unsigned int p)

{ if (p<=SIZE) return -1; //better to throw an exception

return iArray[p];

}

code for arrays inside the objects, always better to throw exceptions rather than terminating the functions


Namespaces – enable C++ programmer to prevent pollution of global namespace that lead to name clashes Global namespace refer to the entire source code. It

Includes all the directly and indirectly included header files.

By default, name of each class is visible in the source code

i.e. in the global space. This can lead to problems.

Suppose a class with same name is defined in 2 header files.

/*A1.h*/

class A

{ };

class B

{ };

Lets include both these header files in a program and see what happens if we declare objects of the class


//multidef01.cpp#include “A1.h”#include “A2.h”

void main()

{ A Aobj; //Ambiguity error due to multiple definitions of A

}

Code showing a reference to a globally declared class can lead to

ambiguity error.

Global visibility of definition of class A make the inclusion of 2 header

Files mutually exclusive. Consequently, this makes use of 2 definitions of

class A mutually exclusive.

An application accesses both definitions of class A simultaneously by

enclosing 2 definitions of the classin separate namespaces can overcome

this problem.


/*A1.h*/

namespace A1

{

class A

{ };

} /*end of namespace A1.h*/

/*A2.h*/

namespace A2

{

class A

{ };

} /*end of namespace A2.h*/


The 2 definitions of class are enveloped in 2 differentNamespaces.

Corresponding namespaces, followed by SRO, must beprefixedto the class name while referring to It anywhere in the sourcecode. Hence the ambiguity encountered in above listing can beovercome.Revised definition of main() function #include “A1.h”#include “A2.h”void main(){ A1::A Aobj1; //ok: Aobj1 is an object of class defined in A1.h

A2::A Aobj2; //ok: Aobj2 is an object of class defined in A2.h} enclosing classes in namespaces prevent pollution of

namespaces


Qualifying the name of the class with that of the Namespace

can be cumbersome.

The using directive enable us to make class definition inside

A namespace visible so that qualifying the name of referred

Class by name of namespace is no longer required. Code below

tells how this is done

/*using.cpp*/

#include “A1.h”

#include “A2.h”

void main()

{ using namespace A1;

A1::A Aobj1; //ok: Aobj1 is an object of class defined in A1.h

A2::A Aobj2; //ok: Aobj2 is an object of class defined in A1.h

} using directive makes qualifying of referred class names by names of enclosing namespaces unnecessary


Using directive brings back global namespace pollution

That namespaces mechanism was supposed to remove in the

first place!

The last line in above listing compiles only because the

classname was qualified by the name of namespace.

Having long name for namespaces. Qualifying the name of a

class i.e. enclosed within such name of namespace is

cumbersome


/*longname1.cpp*/

name_space a_very_very_long_name

{ class A

{ };

}

void main()

{a_very_very_long_name::A A1; //cumbersome long name

} Assigning a suitably short alias to such a long name solves the problem

/*longname2.cpp*/


{ class A { };

}

namespace x=a_very_very_long_name;


/*longname2.cpp*/


{ class A { };

}

namespace x=a_very_very_long_name;

Void main()

{

X::A A1; //convenient short name

}


Aliases – provide an incidental benefit also. If alias name has been used at a number of places in the source code. Changing the alias declaration so that it stands as an alias for a different namespace will make each reference of enclosed class refer to a completely different class

Suppose an alias x refers to a namespace ‘N1’.

namespace x = N1; //declaring an alias

Further suppose this alias has been used extensively in code

X::A Aobj; //Aobj is an object of class A i.e. enclosed in namespace N1

Aobj.f1(); //f1() is a member function of above class

If declaration of alias is changed to namespace N2,

Namespace x=N2;

Then all existing qualifications of referred class names that use x would now

refer to a class A i.e. contained in namespace N2.


Nested Classes – A class can eb defined inside another class. Such a class is called Nested class. A class that contain a nested class is called Enclosing class. Nested classes are defined in private, protected, or public portions of enclosing class

• Class B is defined in the private section of the class.

/*nestedprivate.h*/

Class A

{

class B

{ /* definition of class B*/

{/* definition of class A*/

}; /*end of nestedprivate.h*/ Nested classes


Here class B is defined in public section of class A. A nested class is created if it doesn’t have any relevanceoutside its enclosing class. Naming Collision can be avoided with nested class

Class A /*nestpublic.h*/

{

public:

class B

{/* definition of class B*/

};

/*definition of class A*/

}; A public nested class


In the listings of the 2 slides , even If there is a class B

defined as A global class, its name will not clash with the

nested class B.

The size of objects of an enclosing class is not affected by

the presence of nested class. //size.cpp

How are members of a nested class defined ?

Members of a nested class can be defined outside the definition

of the enclosing class by prefixing the function name with name of

enclosing class followed by SRO. This inturn is followed by name

of nested class followed again by SRO.


Class A /*nestclassdef.h*/

{

public:

class B

{ public:

void BTest(); //prototype only

}; //definition of class A

}

#include “nestclassdef.h”

void A::B::BTest()

{ //definition of A::B::BTest() function

}

/* definition of rest of functions of class B*/

Code Defining member functions of nested classes


A nested class may be only prototyped within its enclosing class and defined later. Again , name of enclosing class with SRO is required.

Class A /nestclassdef.h

{ class B; //prototype only

};

Class A::B

{ /*definition of the class B*/

}

Defining a nested class outside the enclosing class.

Objects of nested class are defined outside the member functions of the enclosing class followed by SRO(scope resolution operator) A::B B1; line will compile only if class B is

defined within public section of class A, else compile time error occurs


An Object of the nested class an be used in any of the

member functions of the enclosing class without the

scope resolution operator. Moreover an object of nested

Class can be a member of enclosing class.

In either case ,only the public member functions of the object

can be accessed unless the enclosing class is a friend of the

nested class


//nestlclassobj.hClass A{

class B{

public: void ATest();

};}; //nestclassobj.cpp#include “nestclassobj.h”void A::ATest(){ B1.BTest();

B B2;B2.BTest();

} Declaring objects of nested class in the member functions of the enclosing class


Member functions of the nested class can access the nonstatic publicmembers of the enclosing class through an object, a pointer, or a referenceonly.

//enclclassobj.h

Class A

{

Public:

void ATest();

class B

{

public:

void BTest();

void BTest1();

};

};


//enclclassobj.cpp#include “enclclassobj.h”

void A::B::BTest(A& ARef)

{ ARef.ATest() //ok

}

void A::B::BTest1()

{

ATest();//Error

}

Accessing nonstatic members of the enclosing the class in

member functions of the nested class.


It can be observed that an error is produced when a direct

Access is made to the member of the enclosing class

through the function of the nested class.

CREATION OF AN OBJECT OF A NESTED CLASS DOES

NOT CAUSE AN OBJECT OF ENCLOSING CLASS TO BE

CREATED.

The classes are nested to merely control the visibility.

Since A::B::BTest() function will be called with respect to an object

Of class B, a direct access to a member of the enclosing class A can be made through an object of that class only.


object oriented programming with c++

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