My c++

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C++ (C with Classes)

Object Oriented Programming (OOP)

The term ‘‘Object Oriented Programming” means a

programming

language that fully supports the object oriented (features) style of

programming.

Introduction

C++ is an object-oriented programming language developed by

Bjarne Stroustrup at AT & T Bell Labs in the early 1980’s.

Since the class concept was the major addition to the original C

language, it is called as "C with classes". However later in 1983, the

name was changed to C++. The idea of C++ comes from the 'C'

increment operator "++", there by suggesting that C++ is an

incremented version of 'C'.

C++ is a superset of C. Therefore almost all C programs are valid C++

programs.

Difference between C & C++

‘C’ is a procedure-oriented programming language where

everything is placed in the form of procedures or functions. While we

concentrate on functions very little attention is given to the data that

are being used by various functions & any function can access the

information provided in other functions. It doesn’t model the real world

problems very well. It employs top-down approach in program design.

Where as ‘C++’ is an object-oriented programming language which

treats data as a critical element in the program and it doesn’t allow

moving freely around the system. It binds the data & the functions that

operate on data together and protects it from accidental use of other

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functions. OOP allows us to decompose a problem into a number of

entities called objects and built data and functions around these

objects.

Advantages of OOP

1. Object Oriented Approach

2. Closer to real world object

3. Dynamic Declaration

4. Data Security

5. Code Re-Usability & Extensibility

Basic concepts of ‘Object-Oriented’ programming language

Class

A class is a blueprint or prototype that defines the variables and the

methods common to all objects of a certain kind.

A class is a logical construct of an object.

A class is an abstract representation of something, whereas an object

is a usable example of the class.

A class is an expanded concept of a structure in C, instead of holding

only data; it can hold both data and functions. Once a class has been

defined, you can create any number of objects based on that class.

Object

An object is an instance (example or illustration) of a class. In

terms of variables, a class would be the data type and an object

would be the variable.

An object is a physical reality.

An object is a software bundle of related variables and methods.

Software objects are often used to model real-world objects you find in

everyday life.

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Polymorphism (many forms)

An ability to have more than one function with the same name,

each having different functionality. The function going to execute is

determined at run time. Polymorphism refers to the fact that a single

operation can have different behavior in different objects.

E.g.: Overloading, Overriding.

Overloading:

Overloading is the practice of supplying more than

one definition for a given function name in the same scope. The

compiler is left to pick the appropriate version of the function or

operator based on the arguments with which it is called.

Inheritance

The mechanism of creating new classes by deriving the features

from existing classes is called Inheritance.

In OOP the concept of inheritance provides the idea of reusability &

extensibility. This means that we can add additional features of an

existing class without modifying it. This is possible by deriving a new

class from the existing one. The new class will have the combined

features of both the classes.

Encapsulation

The method of packing all the data members & member

functions into a single unit called class and the process is called

‘Encapsulation’

Data Hiding

The process of hiding the data members and member functions

from access by the other class objects other than the same class

objects.

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The data is not accessible to the outside world and only those

functions which are placed in the class can access it, these functions

provide the interface between objects data and the program. The

insulation of data from direct access by the program is called data

hiding.

Data Abstraction

It is the process of accessing the data members & member

functions with the objects.

Abstraction refers to the act of representing essential features without

including the background details and explanations. Classes use the

concept of abstraction and defined as a list of abstraction attributes.

Since the classes use the concept of data abstraction they are known

as Abstract Data Type (ADT).

Data Binding

Binding refers to the act of associating an object or a class with

its member. If we can call a method fn() on an object o of a class c, we

say that the object o is binded with the method fn(). This happens at

compile time and is known as static or compile - time binding.

The calls to the virtual member functions are resolved during run-time.

This mechanism is known as dynamic binding. The most prominent

reason why a virtual function will be used is to have a different

functionality in the derived class. The difference between a non-virtual

member function and a virtual member function is the non-virtual

member functions are resolved at compile time.

Structure of C++ program:

Include files

Class declaration

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Member functions definition

Main function

{

Local declaration;

Object declaration;

Executable coding;

}

Syntax for Class Declaration

class class_name

{

access_specifier_1:

data members;

access_specifier_2:

member functions;

……….

} object_names;

where class_name is a valid identifier for the class, object_names is an

optional list of names for objects of this class. The body of the

declaration can contain members, which can be either data or function

declarations, or optionally access specifiers.

All is very similar to the declaration on structures, except the new

thing called access specifier.

An access specifier is one of the following three keywords:

private, public or protected. These specifiers modify the access rights

that the members following them acquire:

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private members of a class are accessible only within the class

and by the public members of the same class or from their

friends.

protected members are accessible from members of their same

class and from their friends, but also from members of their

derived classes.

public members are accessible from anywhere in the program

where the object is visible.

By default, all members of a class declared with the class keyword

have private access for all its members.

Function Definitions outside the class

Member functions that are declared inside a class have to be

defined separately outside the class. They should have a function

definition outside the class as

return_type class_name :: function_name(arguments list)

{

function body;

}

The membership label class_name :: tells the compiler that the

function belongs to the class class_name. That is the scope of the

function is restricted to the class_name specified in the header line.

The symbol "::" is called Scope Resolution operator.

The scope operator (::) specifies the class to which the member being

declared belongs, granting exactly the same scope properties as if this

function definition was directly included within the class definition.

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The only difference between defining a class member function

completely within its class and to include only the prototype and later

its definition, is that in the first case the function will automatically be

considered an inline member function by the compiler, while in the

second it will be a normal (not-inline) class member function, which in

fact supposes no difference in behavior.

Inline Function

They are shortcut functions that are not actually called; rather

their code is expanded at the point of execution. If a function is

declared with the keyword inline, the compiler does not call the actual

function instead it copies the code from the inline function directly into

the calling function.

Inline is a hint to the compiler that you would like the function to be

inlined. The compiler is free to ignore the hint and make a real function

call.

this pointer:

"this" is a pointer that points the address of the current object.

The unique pointer is automatically passed to a member function when

it is called. The pointer "this" acts as an implicit argument to all the

member functions.

Object Arrays

We know that an array can be of any data type including struct,

similarly we can also have arrays of variables that are of the type

class. Such variables are called arrays of objects.

class employ

{

char name[10];

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int age;

public:

void inputdata();

void outputdata();

};

ex:-

employ emp[5];

Create A Class With The Name Bank And Create An Array With 5 Cells

And Accept Data And Print Data.

Example for an Object Arrays.

# include <stdio.h>

# include <iostream.h>

# include <conio.h>

class bank

{

int acno,cbal;

char cname[20];

public:

void input();

void output();

};

void bank::input()

{

cout<<"ENTER A/C NUMBER :";

cin>>acno;

cout<<"ENTER CUSTOMER NAME :";

cin>>cname;

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cout<<"ENTER CURRENT BALANCE :";

cin>>cbal;

}

void bank::output()

{

cout<<"ACCOUNT NUMBER IS :"<<acno<<endl;

cout<<"CUSTOMER NAME IS :"<<cname<<endl;

cout<<"CURRENT BALANCE IS :"<<cbal<<endl;

}

void main()

{

int i;

bank b[5];

for(i=0;i<5;i++)

{

cout<<"ENTER VALUES FOR CELL :"<<i<<endl;

b[i].input();

}

clrscr();

for(i=0;i<5;i++)

{

cout<<"THE VALUES OF THE CELL:"<<i<<endl;

b[i].output();

getch();

}

}

Stream

A stream is defined as a collection of pre-defined objects. The

iostream (Input/Output stream) defines the following two objects.

cout

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cout is an object, defined in standard output stream(ostream).

The standard output stream normally flows to the screen. cout is an

object of the class ostream_withassign, which is derived from ostream

class.

<<

The operator << is called insertion or put to operator. It directs

the contents of the variable on its right to the object on its left.

Screen <----- cout <----- << <--- variable

e.g; screen<---cout<<"welcome";

cin

cin is an object, defined in standard input stream (istream). This

stream represents data coming from the keyboard. cin is an object of

istream_withassign class, which is derived from istream class.

>>

This operator is called extraction or get from operator. It takes

the value from the stream on its left and places it in the variable on its

right.

Keyboard ---> cin ---> >> ---> variable

eg: keyboard-->cin>>x;

Basic Data Types

Built-in-Data types: int, char, float, double, void

User-defined types: structure, union, class, enumeration

Derived types: array, function, pointer, reference

Reference Variable

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A reference variable provides an alias (alternative name) for a

previously defined variable.

Syntax: data_type &ref_var_name = variable;

E.g.: int x = 200;

int &xref = x;

A reference variable must be initialized at the time of declaration. This

establishes the correspondence between the reference and the data

object that it names. Here the "&" is not an address operator. The

notation datatype followed by "&" means that it is the reference to

that datatype.

Example for Reference Variable

#include <stdio.h>

#include <conio.h>


void main()

{

int a=200;

int &b=a;

int &c=b;

clrscr();

cout<<"A VALUE IS :"<<a<<endl;

cout<<"B VALUE IS :"<<b<<endl;

cout<<"C VALUE IS :"<<c<<endl;

getch();

b=55;




getch();

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c=3500;




getch();

}

Default Arguments

C++ allows calling a function without specifying all its

arguments. In such cases the function assigns a default value to the

parameter which does not have a matching argument in the function

call. We have to specify the default values when the function is

declared. The compiler looks at the prototype (declaration) to see how

many arguments the function uses and alerts the program for possible

default values. One important point is that only the trailing arguments

can have default values i.e. you must add default from right to left. It is

not possible to provide a default value to a particular argument in the

middle of the argument list.

Ex: int add (int x, int y=0, int z=0);

int mul (int a=1,int b=20,int c=40)

Ex: add (10,20,30);

add (10,20);

add (10);

add (); does not allow because there is no default

value for argument x.

Another Example for Default arguments


# include <stdio.h>

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# include <conio.h>

int add(int a,int b,int c=0,int d=0,int e=0)

{

return (a+b+c+d+e);

}

void main()

{

int m,n,p,q,r;

clrscr();

cout<<"ENTER ANY FIVE INTEGERS :"<<endl;

cin>>m>>n>>p>>q>>r;

cout<<"ADDITION OF 2 NUMBERS

ARE :"<<add(m,n)<<endl;

cout<<"ADDITION OF 3 NUMBERS ARE :"<<add(m,n,p)<<endl;

cout<<"ADDITION OF 4 NUMBERS ARE :"<<add(m,n,p,q)<<endl;

cout<<"ADDITION OF 5 NUMBERS ARE :"<<add(m,n,p,q,r)<<endl;

getch();

}

Memory Management Operators (Dynamic Memory Allocation)

The part of the computer memory available to programmers, is

divided into two areas: The Stack and The Heap (or Free Store).

The Stack is used for those items that have a definite size and

lifetime, for

example, variables, arrays, etc. All the elements of a program where

they are

explicitly defined before compilation are stored ‘statically’.

The Heap represents the remaining unused memory. This part of

memory is

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generally used during the execution of the program. Any object that is

created at

run time is a dynamic object. Such an object has an unknown size and

lifetime.

Creating dynamic objects is very useful in creating highly interactive

programs.

Memory Management operators:

C uses malloc() and calloc() functions to allocate memory

dynamically at runtime. Similarly it uses the function free() to free

dynamically allocated memory. Although C++ supports these

functions, it also defines two unary operators 'new' and 'delete' that

perform the task of allocating and freeing the memory in a better and

easier way. Since these operators manipulate memory on the free

store, these are also known as free store operators.

To allocate the memory space dynamically during run time we

can use ‘new’ operator & in order to free the memory space which is

allocated with ‘new’ we can use the operator ‘delete’.

The 'new' operator can be used to create objects of any type.

Syntax:

pointer_variable_name = new datatype

Here pointer_variable is a pointer of type datatype. The new

operator allocates sufficient memory to hold a data objects of TYPE

datatype and return the address of the object. The datatype may be

any valid datatype. The pointer variable holds the address of the

memory space allocated.

E.g. int *p;

float *q;

p = new int[10];

q = new float [20];

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Where p is a pointer of type int and q is a pointer of type float.

When a data object is no longer needed, it is destroyed to

release the memory space for reuse, in that case we can use 'delete'

operator.

Syntax:

delete pointer_variable;

The pointer_variable is the pointer that points to a data object

created with new operator.

E.g. delete p;

delete []p//for freeing an array of size

delete q;

sales s;

sales *q;

q =&s;

qinput() or sales.input();

qprint() or sales.print();

Example Program for Dynamic Memory Allocation.


# include <stdio.h>

# include <conio.h>

void main()

{

int n,*a,*p;

clrscr();

cout<<"ENTER NUMBER OF CELLS";

cin>>n;

a=new int[n];

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for(p=a;(p-a)<n;p++)

{

cout<<"ENTER ANY VALUE TO ARRAY :";

cin>>*p;

}

clrscr();

for(p=a;(p-a)<n;p++)

{

printf("THE CELL NUMBER IS %d\t:",(p-a));

printf("THE CELL ADDRESS IS \n:",p);

cout<<"VALUE OF ARRAY :"<<*p<<endl;

}

delete a;

getch();

}

Example Program for Object Arrays with Dynamic Memory Allocation.


# include <stdio.h>

# include <conio.h>

class st

{

int sno, m1, m2, m3;

char sna[20];

public:

void accept()

{

cout<<"ENTER STUDENT NUMBER:";

cin>>sno;

cout<<"ENTER STUDENT'S NAME:";

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cin>>sna;

cout<<"ENTER THE MARKS OF THREE SUBJECTS:";

cin>>m1>>m2>>m3;

}

int get_tot()

{

return(m1+m2+m3);

}

void print()

{

cout<<"STUDENT NUMBER IS:"<<sno<<endl;

cout<<"STUDENT'S NAME IS:"<<sna<<endl;

cout<<"MARKS IN THREE SUBJECTS ARE:"<<m1<<"\t"<<m2<<"\

t"<<m3<<endl;

}

};

void main()

{

st *p,*p1;

int tot,av,n;

clrscr();

cout<<"ENTER NUMBER OF CELLS :";

cin>>n;

p=new st[n];

for(p1=p;(p1-p)<n;p1++)

p1->accept();

clrscr();

cout<<"THE VALUE OF THE ARRAY IS :";

for(p1=p;(p1-p)<n;p1++)

{

tot=p1->get_tot();

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av=tot/3;

printf("THE ADDRESS OF CELL IS \n",p1);

cout<<"THE VALUE OF CELL IS :"<<(p1-p)<<endl;

p1->print();

cout<<"TOTAL MARKS ARE :"<<tot<<endl;

cout<<"AVERAGE MARKS ARE :"<<av<<endl;

getch();

}

delete p;

}

Function Overloading

'Function overloading' means we have to perform the different

operations by using the same method.

The compiler will come to know the execution of a particular function

depending on the maching of number of arguments & their return type

during the function call

Ex: int sum(int)

int sum(int,int)

void sum(float, int)

void sum(float, int,int)

In the above example we are using the same method 'sum' but

the first method 'sum' performing it's operation by taking only one

argument of 'type' & the second method 'sum' performing its operation

by taking two arguments of type 'int' and so on.

Ex:sum(15) //will make a call to first function sum

sum(25,60)//will make a call to second function sum

STATIC MEMBERS

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If we want to declare the data members that is common to all

the objects created in that class we have to declare those data

members as the static data members & the syntax for declaring static

data member is

static data-type variable-name; Ex: static int a;

The above data member 'a' will be shared by all the objects created in

that class i.e only one copy of that data member is created for all the

object without creating a separate copy. Whenever we create a data

member as a static it will be initialized to '0' automatically, and we can

define the value for the static data members outside the class i.e with

the help of the scope resolution operator & it's syntax is

data-type class-name :: data-member-name=value

Ex:

int example :: a; It means the value of a is initialized to 0

int example :: a=10; It means the value of a is initialized to 10

Static member function:

We can also declare a member function as a static. The syntax

for declaring a member function as static is

Syntax: static return-type function-name(arguments);

Inheritance:

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The process of creating a new class by deriving the features from

existing

classes. It provides the concept of reusability & extensibility.

The term 'reusability' means the ability to use the data provided in

one class by another class & 'Extensibility' provides the ability to add

some more data members & member functions to the already existing

class

The main class is called as 'base class' & the class which is acquiring

the features of the base class is called as derived class & the syntax

for defining the derived class is

class derived_class_name : access_specifier base_class_name

{

//data members & member function of derived class

}

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The 'access-specifer' specifies the method of accessing the

information provided in the base class & it will be accessed in any one

of the three ways.

1. private

2. protected

3. public

Inheriting in private mode: If the derived class acquires the

features of base class in private mode

base derived

private will become private

protected '' private

public private

Inheriting in protected mode: If we acquire the features of base

class in 'protected mode' its characteristics will be

base derived


protected " protected

public " protected

Inheriting in public mode: In 'public' access specifier the following

the characteristics of the base class in derived class

base derived


protected " private

public " public

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In all the above three cases the 'private' data members of the

base class is not inheritable. If we want to access those 'private' data

members we have to declare a function in 'public' mode in the base

class & with that member function we can access them in the derived

class

If we want to define those data members in the derived class itself we

have declare those data members in 'protected' mode, but these will

be available up to one level only i.e it's accessible to the immediate

class which is accessing it's features

Both 'private' & 'protected' data members are not accessible in the

main() function. 'public' data-members & member functions will be

accessible anywhere in our program i.e they are accessible in the

main() function also

Reusability is another important feature of OOP. It is always nice if we

could reuse something that already exists rather than trying to create

the same all over again. C++ strongly supports the concept of

reusability. The C++ classes can be reused in several ways. Once a

class has been written and tested, it can be adopted by other

programmers to send their requirements. Creating new classes,

reusing the properties of the existing ones basically does this. The

mechanism of deriving a new class from an old one is called

"Inheritance" (or derivation). The old class referred to as the base class

and the new one is called derived class.

The derived class inherits some or all the properties of the base

class. A class can also inherit properties from more than one class of

from more than one level.

A derived class with only one base class is called single

inheritance, and one derived class with several base classes is called

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multiple inheritance. On the other hand, the properties of one class

may be inherited by more than one class. This process is known as

hierarchical inheritance. The mechanism of deriving a class from

another derived class is known as multilevel inheritance. The

combination of any of two inheritances is called hybrid inheritance.

Defining a Derived Class

A derived class is defined by specifying it's relationship with the

base class in addition to it's own details.

Syntax: class derived class_name : visibility_mode base class

name

{

- - - - - - - -

- - - - - - - - //members of derived class

- - - - - - - -

};

The colon (:) indicates that the derived class name is derived

from the base class name. The visibility mode is optional and if

present, it may be either private or public. The default visibility mode

is private. This mode specifies whether the features of the base class

are privately derived or publicly derived.

When a base class is privately inherited by a derived class,

‘public members’ of the base class become ‘private members’ of the

derived class and therefore the public members of the base class can

only be accessed by the member functions of the derived class. They

are inaccessible to the objects of the derived class. A public member of

a class can be accessed by its own objects using the dot operator. The

result is that no member of the base class is accessible to the objects

of the derived class.

When a base class is publicly inherited by a derived class, public

members of the base class becomes the pubic members to the derived

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class and therefore they are accessible to the objects of the dedrived

class.

In both the cases private members are not inherited and

therefore the private members of a base class will never become the

members of it's derived class.

E.g.:

class B:public A

{

- - - - - - //members of class B

- - - - - -

- - - - - -

- - - - - -

};

Example Program for Single Inheritance.


# include <conio.h>

class a

{

int x,y;

void input(int p,int r)

{

x=p;

y=r;

}

void print()

{

cout<<"X VALUE IS :"<<x<<endl;

cout<<"Y VALUE IS :"<<y<<endl;

}

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class b:public a //deriving a derived class

{

int m,n;

public:

void accept()

{

cout<<"ENTER TWO INTEGERS :";

cin>>m,n;

}

void display()

{

cout<<"M VALUE IS :"<<m<<endl;

cout<<"N VALUE IS :"<<n<<endl;

}

};

void main()

{

b t; //object declared for class b

clrscr();

t.input(253,445);//member function of base class

t.accept(); //function of the derived class

clrscr();

t.print(); //function of the base class

t.display(); //function of the derived class

getch();

}

Example Program for Multilevel Inheritance or a Derived Class from

another Derived Class.


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# include <stdio.h>

# include <string.h>

# include <conio.h>

class student

{

int sno;

char sna[10],sadd[10];

public:

void input()

{

cout<<"ENTER STUDENT NUMBER :";

cin>>sno;

cout<<"ENTER STUDENT'S NAME :";

cin>>sna;

cout<<"ENTER STUDENT'S ADDRESS :";

cin>>sadd;

}

void output()

{

cout<<"STUDENT NUMBER IS "<<sno<<endl;

cout<<"STUENT'S NAME IS "<<sna<<endl;

cout<<"STUDENT'S ADDRESS IS "<<sadd<<endl;

}

};

class fees:public student

{

int tf,fp,due;

char cou[10];

public:

void accept()

{

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cout<<"ENTER COURSE NAME :";

cin>>cou;

cout<<"ENTER TOTAL FEE :";

cin>>tf;

cout<<"HOW MUCH FEE IS PAID :";

cin>>fp;

due=tf-fp;

}

void display()

{

cout<<"COURSE NAME IS :"<<cou<<endl;

cout<<"TOTAL FEE IS :"<<tf<<endl;

cout<<"FEE PAID IS :"<<fp<<endl;

cout<<"DUE FEE IS :"<<tf-fp<<endl;

}

};

class marks:public fees

{

int tm,mm,mp,mc,am;

char res[15];

public:

void marksin()

{

cout<<"ENTER MARKS IN MATHS :";

cin>>mm;

cout<<"ENTER MARKS IN PHYSICS :";

cin>>mp;

cout<<"ENTER MARKS IN CHEMISTRY :";

cin>>mc;

}

void resout()

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{

tm=mm+mp+mc;

am=tm/3;

if(am>75)

strcpy(res,"DISTINCTION");

else if(am>=60)

strcpy(res,"FIRST CLASS");

else if(am>=50)

strcpy(res,"SECOND CLASS");

else if(am>=35)

strcpy(res,"THIRD CLASS");

else

strcpy(res,"FAILED");

cout<<"MARKS IN MATHS ARE :"<<mm<<endl;

cout<<"MARKS IN PHYSICS ARE :"<<mp<<endl;

cout<<"MARKS IN CHEMISTRY ARE :"<<mc<<endl;

cout<<"TOTAL MARKS ARE :"<<tm<<endl;

cout<<"AVERAGE MARKS ARE :"<<am<<endl;

cout<<"RESULT IS--------------:"<<res<<endl;

}

};

void main()

{

clrscr();

marks obj; //object declaration

obj.input();//member function of class student

obj.accept();//member function of class fees

obj.marksin();//member function of class marks

clrscr();

obj.output(); //member function of class student

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obj.display();//member function of class fees

obj.resout();//member function of class marks

getch();

}

Multiple Inheritance:

A class can inherit the attributes of two or more classes. This is

known as multiple inheritance. Multiple inheritance allows combining

the features of several existing classes as a starting point for defining

a new class.

Syntax:

class derived_class : visibility label base class, visibility label base

class………

{

-- - - - - - - - - -

- - - - - - - - - - -

- - - - - - - - - - -

- - - - - - - - - - -

}

Where visibility label is either public or private. Comma separate

the base classes.

Protected Members:

C++ provides a third visibility modifier protected, which serve a

limited purpose in inheritance. A member declared as protected is

accessible by the member functions with in its class and any class

derived from it as the public member of the base class. It cannot be

accessed by the functions outside these classes.

- 30 -

When a protected member is inherited in public mode, it

becomes protected in the derived class too and therefore it is

accessible by the member functions of the derived class. It is also

ready for further inheritance.

A protected member is inherited in the private mode derivation,

that becomes private in the derived class. Although it is available to

the member functions of the derived class. It is not available for further

inheritance since private members cannot be inherited.

E.g.:

class A

{

protected:

int a;

- - - - - - -

- - - - - - -

- - - - - - -

};

class B:public A

{

- - - - - - //members of class A are

- - - - - - //protected to class B

- - - - - -

};

class C:private B

{

- - - - - - //members of class A are

- - - - - - //private to class C

- - - - - -

};

- 31 -

class D:public C

{

- - - - - - //members of class A cannot be

- - - - - - //accessed in class D

- - - - - -

};

Example Program For Multiple Inheritance And Protected Members.

(Two Or More Base Classes One Derived Class Is Called Multiple

Inheritance).


# include <conio.h>

class employ

{

protected:

int eno,bs;

char ena[10],eadd[15];

public:

void input()

{

cout<<"ENTER EMPLOY NUMBER :";

cin>>eno;

cout<<"ENTER EMPLOY NAME :";

cin>>ena;

cout<<"ENTER EMPLOY ADDRESS :";

cin>>eadd;

cout<<"ENTER BASIC SALARY :";

cin>>bs;

}

};

- 32 -

class allow

{

protected:

int da,hra,cca;

public:

void accept()

{

cout<<"ENTER DA:";

cin>>da;

cout<<"ENTER HRA:";

cin>>hra;

cout<<"ENTER CCA:";

cin>>cca;

}

};

class ded

{

protected:

int pf,it;

public:

void dedinput()

{

cout<<"ENTER PROVIDENT FUND:";

cin>>pf;

cout<<"ENTER INCOME TAX:";

cin>>it;

}

};

class salary:public employ,public allow,public ded

{

int tall,tded,gs,ns;

- 33 -

public:

void calc_sal()

{

tall=da+hra+cca;

tded=pf+it;

gs=bs+tall;

ns=gs-tded;

}

void output()

{

cout<<"EMPLOY NUMBER IS:"<<eno<<endl;

cout<<"EMPLOY NAME IS :"<<ena<<endl;

cout<<"EMPLOY ADDRESS IS :"<<eadd<<endl;

cout<<"BASIC SALARY IS :"<<bs<<endl;

cout<<"EMPLOY'S DA IS :"<<da<<endl;

cout<<"EMPLOY'S HRA IS :"<<hra<<endl;

cout<<"EMPLOY'S CCA IS :"<<cca<<endl;

cout<<"EMPLOY'S PF IS :"<<pf<<endl;

cout<<"EMPLOY'S IT IS :"<<it<<endl;

cout<<"TOTAL ALLOWANCES :"<<tall<<endl;

cout<<"TOTAL DEDUCTIONS :"<<tded<<endl;

cout<<"EMPLOY'S GROSS SALARY IS :"<<gs<<endl;

cout<<"EMPLOY'S NET SALARY IS :"<<ns<<endl;

}

};

void main()

{

salary s;

s.input();

s.accept();

s.dedinput();

- 34 -

clrscr();

s.calc_sal();

s.output();

getch();

}

Hierarchical Inheritance:

In the hierarchical inheritance different classes are derived from

one base class. A subclass can be constructed by inheriting the

properties of the base class. A subclass can serve as a base class for

the lower classes and so on.

Example Program for Hierarchical Inheritance.


# include <conio.h>

# include<string.h>

class student

{

int sno;


public:

void input()

{

cout<<"ENTER STUDENT'S NUMBER :";

cin>>sno;


cin>>sna;

cout<<"ENTER STUDET'S ADDRESS :";

cin>>sadd;

}

- 35 -

void output()

{

cout<<"STUDENT'S NUMBER IS :"<<sno<<endl;

cout<<"STUDENT'S NAME IS :"<<sna<<endl;

cout<<"STUDENT'S ADDRESS IS :"<<sadd<<endl;

}

};

class lang

{

int mt,me;

public:

void accept()

{

cout<<"ENTER MARKS IN TELUGU :";

cin>>mt;

cout<<"ENTER MARKS IN ENGLISH :";

cin>>me;

}

void display()

{

cout<<"TELUGU MARKS ARE :"<<mt<<endl;

cout<<"ENGLISH MARKS ARE :"<<me<<endl;

}

};

class mathes:public lang

{

int mm,mp,mc;

public:

void sentry()

{


- 36 -

cin>>mm;


cin>>mp;

cout<<"ENTER MARKS IN CHEMISTRY:";

cin>>mc;

}

void sprint()

{



cout<<"MARKS IN CHEMISTRY ARE :"<<mc<<endl;

cout<<"TOTAL MARKS ARE :"<<mt+me+mm+mp+mc<<endl;

}

};

class computers:public lang

{

int mmt,mph,mcs;

public:

void sentry()

{


cin>>mmt;


cin>>mph;

cout<<"ENTER MARKS IN COMPUTERS:";

cin>>mcs;

}

void sprint()

{

cout<<"MARKS IN MATHS ARE :"<<mmt<<endl;

cout<<"MARKS IN PHYSICS ARE :"<<mph<<endl;

- 37 -

cout<<"MARKS IN COMPTERS ARE :"<<mcs<<endl;

cout<<"TOTAL MARKS

ARE :"<<mt+me+mmt+mph+mcs<<endl;

}

};

class arts:public lang

{

int mhs,mec,mci;

public:

void sentry()

{

cout<<"ENTER MARKS IN HISTORY :";

cin>>mhs;

cout<<"ENTER MARKS IN ECONOMICS:";

cin>>mec;

cout<<"ENTER MARKS IN CIVICS :";

cin>>mci;

}

void sprint()

{

cout<<"HISTORY MARKS ARE :"<<mhs<<endl;

cout<<"ECONOMICS MARKS ARE :"<<mec<<endl;

cout<<"CIVICS MARKS ARE :"<<mci<<endl;

cout<<"TOTAL MARKS ARE :"<<mt+me+mhs+mec+mci<<endl;

}

};

void main()

{

mathes m;

computers cs;

arts a;

- 38 -

clrscr();

m.accept();

m.sentry();

clrscr();

cs.accept();

cs.sentry();

clrscr();

a.accept();

a.sentry();

clrscr();

m.display();

m.sprint();

getch();

cs.display();

cs.sprint();

getch();

a.display();

a.sprint();

getch();

}

Example for Hybrid Example. (The Combination Of Any Two Inheritance

Is Called Hybrid Inheritance.


# include <stdio.h>

# include <conio.h>


class student

{

protected:

- 39 -

int sno;


public:

void input()

{

cout<<"ENTER STUENT NUMBER :";

cin>>sno;


cin>>sna;

cout<<"ENTER STUDENT'S ADDRESS:";

cin>>sadd;

}

};

class test:public student

{

protected:

int mm,mp,mc;

public:

void mentry()

{


cin>>mm;


cin>>mp;

cout<<"ENTER MARKS IN CHEMISTRY:";

cin>>mc;

}

};

class sports

{

protected:

- 40 -

int sm;

public:

void sentry()

{

cout<<"ENTER SPORTS MARKS :";

cin>>sm;

}

};

class result:public test, public sports

{

int tot,avg;

char res[20];

public:

void findres()

{

tot=mm+mp+mc;

avg=tot/3;

if(sm>50)

avg=avg+5;

if(avg>=75)

strcpy(res,"DISTINCTION");

else if(avg>=60)

strcpy(res,"FIRST CLASS");

else if(avg>=50)

strcpy(res,"SECOND CLASS");

else if(avg>=35)

strcpy(res,"THIRD CLASS");

else if(avg<35)

strcpy(res,"FAILED");

}

void display()

- 41 -

{

cout<<"STUDENT NUMBER IS :"<<sno<<endl;

cout<<"STUDENT'S NAME IS :"<<sna<<endl;

cout<<"STUDENT'S ADDRESS IS :"<<sadd<<endl;



cout<<"MARKS IN CHEMISTRY ARE:"<<mc<<endl;

cout<<"TOTAL MARKS ARE :"<<tot<<endl;

cout<<"AVERAGE MARKS ARE :"<<avg<<endl;

cout<<"RESULT OBTAINED :"<<res<<endl;

}

};

void main()

{

result r;

clrscr();

r.input(); //member function of student class

r.mentry(); //member function of test class

r.sentry(); //member function of sports class

r.findres(); //member function of result class

clrscr();

r.display();

getch();

}

Friend function

A friend function is a special function which is not a member of

any class but it is declared to access the private member data

& functions provided in that class.

C++ allows a common function to be made friendly with one or

more classes, there by allowing the function to have access to the

- 42 -

private data of these classes, such a function need not be a member of

any of these classes, only thing is to declare that function as a friend to

the class.

Syntax for defining a friend function

class sample

{

private:

member declaration;

public:

member function declaration;

friend return_type function_name(arguments); //friend

};

The function declaration should be preceded by the keyword "friend".

The function definition does not use the keyword friend or the scope

resolution operator "::". The functions that are declared with the key

word friend are known as friend functions. A function can be

declared as a friend in any number of classes.

A friend function should possess the following characteristics

(1)It is not in the scope of the class to which it has been declared

as friend

(2)It cannot be called with the scope resolution operator

(3)It can be invoked just like a normal function without help of any

object

(4)It can be declared either in public or private without affecting its

meaning

(5)Usually it has the objects as arguments

- 43 -

(6)It cannot access the member names directly and has to use an

object name and dot membership operator with each member name

(Ex. s.a);

Friend Function Example.


# include <conio.h>

class sample;

class myclass

{

int a;

public:

void input()

{

cout<<"ENTER VALUE FOR A:";

cin>>a;

}

void output()

{


}

friend int getsum(myclass m,sample a)

};

class sample

{

int x;

public:

void accept()

{

cout<<"ENTER A VALUE :";

- 44 -

cin>>x;

}

//friend function declaration

friend int getsum(myclass m,sample s)

};

int getsum(myclass m,sample s)

{

return(m.a+s.x);

}

void main()

{

myclass c;

sample d;

int t;

clrscr();

c.input();

d.accept();

t=getsum(c,d); //friend function calling

clrscr();

c.output();

d.accept();

cout<<"TOTAL VALUE IS :"<<t<<endl;

getch();

}

2 nd Example for a Friend Function.


# include <stdio.h>

# include <conio.h>

class allow;

- 45 -

class ded;

class employ

{

int eno,bs;

char ena[10];

public:

void accept()

{

cout<<"ENTER EMPLOY NUMBER :";

cin>>eno;

cout<<"ENTER EMPLOY NAME :";

cin>>ena;

cout<<"ENTER BASIC SALARY :";

cin>>bs;

}

friend void calc_sal(employ e,allow a,ded d);

};

class allow

{

int da,hra,cca;

public:

void getallow()

{

cout<<"ENTER DA, HRA, CCA :"<<endl;

cin>>da>>hra>>cca;

}


};

class ded

{

int pf,it;

- 46 -

public:

void getded()

{

cout<<"ENTER PF, IT :"<<endl;

cin>>pf>>it;

}


};

void calc_sal(employ e,allow a,ded d)

{

int gs,ns,tall,tded;

tall=d.pf+d.it+a.cca;

tded=d.pf+d.it;

gs=e.bs+tall;

ns=gs-tded;

clrscr();

cout<<"ENTER EMPLOY NUMBER :"<<e.eno<<endl;

cout<<"ENTER EMPLOY NAME :"<<e.ena<<endl;

cout<<"ENTER BASIC SALARY :"<<e.bs<<endl;

cout<<"DA IS :"<<a.da<<endl;

cout<<"HRA IS :"<<a.hra<<endl;

cout<<"CCA IS :"<<a.cca<<endl;

cout<<"PF IS :"<<d.pf<<endl;

cout<<"IT IS :"<<d.it<<endl;

cout<<"GROSS SALARY IS :"<<gs<<endl;

cout<<"NET SALARY IS :"<<ns<<endl;

}

void main()

{

employ emp;

allow all;

- 47 -

ded s;

clrscr();

emp.accept();

all.getallow();

s.getded();

calc_sal(emp,all,s);

getch();

}

Friend Functions with Objects as Arguments and Return Type.


# include <conio.h>

class test;

class sample

{

int a;

float b;

public:

void input()

{

cout<<"ENTER ANY INTEGER AND FLOAT VALUES :"<<endl;

cin>>a>>b;

}

void display()

{



}

friend sample setsum(sample x,test y);

};

- 48 -

class test

{

int m;

float n;

public:

void accept()

{

cout<<"ENTER INTEGER AND FLOAT :"<<endl;

cin>>m>>n;

}

void print()

{

cout<<"M VALUE IS :"<<m<<endl;

cout<<"N VALUE IS :"<<n<<endl;

}

friend sample setsum(sample x,test y);

};

sample setsum(sample x,test y)

{

sample r;

r.a=x.a+y.m;

r.b=x.b+y.n;

return r;

}

void main()

{

sample s,p;

test t;

clrscr();

s.input();

t.accept();

- 49 -

clrscr();

p=setsum(s,t);

cout<<"VALUE OF FIRST OBJECT IS :"<<endl;

s.display();

cout<<"VALUE OF SECOND OBJECT IS :"<<endl;

t.print();

cout<<"VALUE OF RESULT OBJECT IS :"<<endl;

p.display();

getch();

}

Constructors

A constructor is a special member function whose task is to

initialize the objects or variables of a class. The constructor is invoked

implicitly (automatically) whenever an object is created. It is called

constructor, because it will be called implicitly upon the construction of

an object.

A constructor is declared as follows.

class class_name

{

data members;

public:

class_name(arguments) //constructor

{

statements;

}

};

E.g.:

class sample

{

- 50 -

private:

int a,b;

float x,y;

public:

sample() //constructor function

{

a=100;

b=200;

x=35.15;

y=564.25;

}

};

void main()

{

clrscr();

sample s;

getch();

}

Characteristics of a constructor

1. It should have the same name as the class name

2. They are invoked automatically when the objects are

created.

3. They cannot be called explicitly.

4. Like C++ functions they can have default arguments.

5. They do not return any value not even void

6. They cannot be inherited but the derived class can call the

base class constructor

7. It cannot be virtual

8. We cannot refer to their addresses

- 51 -

9. They will make implicit called to new & delete operator

when memory allocation is required

Types of constructors (3 Types)

1. Default constructor (Non Parameterized): It won’t take any

arguments.

2. Parameterized constructor: It can take any no. of

arguments.

3. Copy constructor: It will take a reference of an object as an

argument.

Example for Constructors


# include <stdio.h>

# include <conio.h>

class test

{

int a;

float b;

long c;

public:

test() //constructor function

{

a=230;

b=654.13;

c=54865;

}

void output()

{

cout<<"INTEGER VALUE IS :"<<a<<endl;

cout<<"FLOAT VALUE IS :"<<b<<endl;

- 52 -

cout<<"LONG VALUE IS :"<<c<<endl;

}

};

void main()

{

clrscr();

test t,s,r;

clrscr();

cout<<"VALUES OF T ARE :"<<endl;

t.output();

cout<<"VALUES OF S ARE :"<<endl;

s.output();

cout<<"VALUES OF R ARE :"<<endl;

r.output();

getch();

}

Example for Constructor Function.


# include <conio.h>

class stud

{

int sno,tf,fp,due;

char sna[10],cou[10];

public:

stud()

{

- 53 -

cout<<"enter student's number :";

cin>>sno;

cout<<"enter student's name :";

cin>>sna;

cout<<"enter course name :";

cin>>cou;

cout<<"enter total fee is :";

cin>>tf;

cout<<"enter fee paid :";

cin>>fp;

due=tf-fp;

}

void output()

{

cout<<"student's number is:"<<sno<<endl;

cout<<"student's name is :"<<sna<<endl;

cout<<"course name is :"<<cou<<endl;

cout<<"total name is :"<<tf<<endl;

cout<<"fee paid is :"<<fp<<endl;

cout<<"due fee is :"<<due<<endl;

}

};

void main()

{

clrscr();

stud s,t,u;

clrscr();

cout<<"values of s"<<endl;

s.output();

cout<<"values of t"<<endl;

- 54 -

t.output();

cout<<"values of u"<<endl;

u.output();

getch();

}

Example for Constructor with Arguments.


# include <conio.h>


class sales

{

int sno,samt;

char sna[10];

public:

sales(int a,char n[],int b)

{

sno=a;

strcpy(sna,n);

samt=b;

}

void output()

{

cout<<"SALES MAN NUMBER IS :"<<sno<<endl;

cout<<"SALES MAN NAME IS :"<<sna<<endl;

cout<<"SALES AMOUNT IS :"<<samt<<endl;

}

};

void main()

- 55 -

{

clrscr();

sales t(100,"RAVI",2500);

sales b=sales(101,"KIRAN",3000);

cout<<"VALUES OF T :"<<endl;

t.output();

cout<<"VALUES OF B :"<<endl;

b.output();

getch();

}

Constructors in derived class:

If the base class contain a constructor with one or more

arguments, then it is mandatory for the derived class to have a

constructor and to pass the arguments to the bas class constructors,

since while applying inheritance we usually create the objects by using

the derived class. Thus, it makes sense for the derived class to pass

arguments to the base class constructor. When both the base class &

derived class contain constructors, the base constructor is executed

first and then the constructor in the derived class is executed.

The syntax for defining the constructor in the derived class is

Constructor(arglist) : initialization-section

{

assignment section

}

Destructor

A destructor as the name implies, is used to destroy the objects

that have been created by a constructor. Like a constructor, the

destructor is also a member function whose name is same as the class

- 56 -

name and is preceded by a tilde (~) symbol. A destructor neither

takes any arguments nor returns any value. It will be invoked

implicitly by the compiler upon exit from the program to clean up the

storage that is no longer accessible.

The destructor fulfills the opposite functionality. It is automatically

called when an object is destroyed, either because its scope of

existence has finished (for example, if it was defined as a local object

within a function and the function ends) or because it is an object

dynamically assigned and it is released using the operator delete.

The destructor must have the same name as the class, but preceded

with a tilde sign (~) and it must also return no value.

The use of destructors is especially suitable when an object assigns

dynamic memory during its lifetime and at the moment of being

destroyed we want to release the memory that the object was

allocated.

Overloading Constructors

Like any other function, a constructor can also be overloaded

with more than one function that have the same name but different

types or number of parameters. Remember that for overloaded

functions the compiler will call the one whose parameters match the

arguments used in the function call. In the case of constructors, which

are automatically called when an object is created, the one executed is

the one that matches the arguments passed on the object declaration:

Important: Notice how if we declare a new object and we want to use

its default constructor (the one without parameters), we do not include

parentheses ():

- 57 -

Operator Overloading

C++ has the ability to provide the special meaning to an existing

operator. The mechanism of giving such special meaning to an

operator is known as operator overloading.

This is done with help of a special function, called operator function,

which describes the task.

Syntax: return_type class_name :: operator op(arg_list)

{

function_body;

}

where return_type is the type of value returned by the specified

operation and op is the operator being overloaded. The keyword

"operator" should precede the "op". operator op is the function

name.

It can be either member function or friend function. The basic

difference is a friend function will have only one argument for unary

operator & two for binary operator. But the member function will have

no arguments for unary operator & one argument for binary operator

Some Operator Which Cannot Be Overloaded Are

1). & ->

2) sizeof() [operator]

3) scope resolution operator(::)

4) conditional operator(:?)

Example for Operator Overloading Of Unary Operator:


# include <conio.h>

class exam

- 58 -

{

int a;

float b;

long c;

public:

exam() //constructor function

{

a=10;

b=25.65;

c=42500;

}

exam operator ++() //operator overloading function

{

a+=100;

b+=100;

c+=100;

return *this;

}

void print()

{




}

};

void main()

{

exam e;

int x=15;

clrscr();

- 59 -

cout<<"VALUE BEFORE FUNCTION CALLING :"<<endl;

e.print();

cout<<"x value is :"<<x<<endl;

++e; //operator function calling

x++;

cout<<"value after function calling "<<endl;

e.print();

cout<<"x value is :"<<x<<endl;

getch();

}

Output: Values before function calling

A value is 10, B value is 25.65, C value is 42000 and X

value is 15.

Values after function calling

A value is 110, B value is 125.65, C value is 142000 and X

value is 16.

Example Program for Operator Overloading a Binary Operator "+":


# include <stdio.h>

# include <conio.h>

class sample

{

int a,b;

float m,n;

public:

- 60 -

void get_data()

{

cout<<"ENTER ANY TWO INTEGERS AND TWO FLOATS :";

cin>>a>>b>>m>>n;

}

void print()

{

cout<<"FIRST INTEGER IS :"<<a<<endl;

cout<<"SECOND INTEGER IS :"<<b<<endl;

cout<<"FIRST FLOAT IS :"<<m<<endl;

cout<<"SECOND FLOAT IS :"<<n<<endl;

}

//operator overloading function

sample operator +(sample s)

{

sample t;

t.a=this->a+s.a;

t.b=this->b+s.b;

t.m=this->m+s.m;

t.n=this->n+s.n;

return(t);

}

};

void main()

{

sample p,q,r;

clrscr();

p.get_data();

q.get_data();

- 61 -

clrscr();

r=p+q; //function calling

cout<<"values of first object :"<<endl;

p.print();

cout<<"values of second object :"<<endl;

q.print();

cout<<"addition object values are :"<<endl;

r.print();

getch();

}

Example Program For Overloading A Binary Operator "*":


# include <stdio.h>

# include <conio.h>

class sales

{

int sno,nou;

char sna[10];

public:

sales() //constructor

{

cout<<"ENTER SALES MAN NUMBER :"<<endl;

cin>>sno;

cout<<"ENTER SALES MAN NAME :"<<endl;

cin>>sna;

cout<<"ENTER NUMBER OF UNITS:"<<endl;

cin>>nou;

}

void print()

- 62 -

{

cout<<"SALES MAN NUMBER IS :"<<sno<<endl;

cout<<"SALES MAN NAME IS :"<<sna<<endl;

cout<<"NUMBER OF UNITS ARE :"<<nou<<endl;

}

int operator *(int n)

{

return(nou * n);

}

};

void main()

{

sales s;

int rpu,samt;

clrscr();

cout<<"ENTER RATE PER UNIT :"<<endl;

cin>>rpu;

clrscr();

samt=s*rpu; //operator function calling

s.print();

cout<<"RATE PER UNIT IS :"<<rpu<<endl;

cout<<"SALES AMOUNT IS :"<<samt<<endl;

getch();

}

Abstract class:

An abstract class is one that is not used to create objects. It is

designed only to act as a base class upon which the other classes may

build.

- 63 -

Polymorphism:

Polymorphism means one name multiple forms. Polymorphism

can be classified into

1. Compile time polymorphism

a. Function overloading

b. Operator overloading

The overloaded member functions are selected for invoking my

matching arguments both type and number. This information is known

to the compiler at the compile time and therefore, the compiler is able

to select the appropriate function for a particular call at the compile

time itself. This is called early binding or static binding or static

linking. It’s also known as compile time polymorphism, early binding

simply means that an object is bound to its function call at compile

time.

2. Runtime polymorphism

a. Virtual functions

The process of selecting the appropriate member function during run

time is known as runtime polymorphism also known as late binding

Pointers to Objects:

Object pointers are useful for creating objects at run-time. We

can also use an object pointer to access the public members of an

object. The syntax for defining a pointer to an object is

Class name pointer-variable-name

Ex: item *ptr;

- 64 -

We can refer to the member functions of item in two ways

Ex: ptr->getdata();//by using ->operator

(*ptr).getdat();

We can also created the objects with the help of new operator as

follows

Item *ptr=new item;

The above statement allocates enough memory for the data members

in the object structure and assigns the address of the memory space to

ptr.

Virtual functions:

A virtual function is a member function of a class, whose

functionality can be over-ridden in its derived classes. It is one that is

declared as virtual in the base class using the virtual keyword. The

virtual nature is inherited in the subsequent derived classes and the

virtual keyword need not be re-stated there. The whole function body

can be replaced with a new set of implementation in the derived class.

How does a Virtual Function work?

Whenever a program has a virtual function declared, a v - table

is constructed for the class. The v-table consists of addresses to the

virtual functions for classes that contain one or more virtual functions.

The object of the class containing the virtual function contains a virtual

pointer that points to the base address of the virtual table in memory.

Whenever there is a virtual function call, the v-table is used to resolve

to the function address. An object of the class that contains one or

more virtual functions contains a virtual pointer called the vptr at the

very beginning of the object in the memory. Hence the size of the

object in this case increases by the size of the pointer. This vptr

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contains the base address of the virtual table in memory. Note that

virtual tables are class specific,

i.e., there is only one virtual table for a class irrespective of the

number of virtual functions it contains. This virtual table in turn

contains the base addresses of one or more virtual functions of the

class. At the time when a virtual function is called on an object, the

vptr of that object provides the base address of the virtual table for

that class in memory. This table is used to resolve the function call as

it contains the addresses of all the virtual functions of that class. This is

how dynamic binding is resolved during a virtual function call.

Rules for virtual functions:

1. The virtual functions must be member of some class

2. They cannot be static members

3 .They are accessed by using object pointers

4. It can be friend of another class

5. We cannot have virtual constructors but we can have virtual

destructors

6. While a base pointer point to any type of the derived object

the reverse is not possible

Pure virtual functions:

When we declare a function as virtual inside the base class and

redefine in the derived class the function defined inside the base class

is seldom used for performing any task. It only serves as a placeholder.

Such functions are called do-nothing functions.

A do-nothing function may be defined as follows

Virtual void display() = 0;

Such functions are called pure virtual functions

File Streams

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Remember that a C++ program views input (or output) as a

stream

of bytes. On input, a program extracts (>>) bytes from an input

stream.

On output, a program inserts (<<) bytes into the output stream. The

stream acts as a mediator between the program and the stream's

source

or destination.

In this same manner, input and output data is handled by use of a

stream buffer.

A buffer is a block of memory used as an intermediate, temporary

storage

area for the transfer of information between a program and a device

(e.g.

file).

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Many real-life problems handle large volumes of data and in such

situations we need to use some of the devices such as floppy disk or

hard disk to store the data. The data is stored in these devices using

the concept of files. A file is a collection of related data stored in a

particular area on the disk. Programs can be designed to perform the

read and write operations on these files

A program typically involves either or both of the following kinds

of data communication

(1) Data transfer between the console unit and the program

(2) Data transfer between the program and a disk file

The I/O system of C++ contains a set of classes that define the file

handling methods. These include ifstream, ofstream and fstream.

These classes are derived from fstreambase

Class Contents

fstreambase Provides operations common to the file stream.

Serves as a base for fstream, ifstream and ofstream

class. Contains open() and close() functions

ifstream Provides input operations. Contains open() with

default

input mode. Inherits the functions get(),getline(),

read(),

seekg() and tellg() functions from ostream

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ofstream Provides output operations. Contains open() with

default output mode. Inherits put(), seekp(), tellp()

and write()

functions from ostream

fstream Provides support for simultaneous input and output

operations. Contains open() with default input mode.

Inherits all the functions from istream and ostream

classes through iostream

For opening a file we must first create a file stream and then link

to the file name. A file stream can be defined using the classes

ifstream, ostream, and fstream that are contained in the header file

fstream. The class to be used depend upon the purpose, that is,

whether we want to read data from file or write data to it. A file can be

opened in two ways.

(1)Using the constructor function of the class

(2)Using the member function open() of the class

The first method is used when we use only one file in the system.

The second method is used when we want manage with multiple files

using one stream.

Opening file using constructor:

A constructor is used to initialize an object while it is being

created. Here a file name is used to initialize the file stream object.

This involves the following steps

1. Create a file stream object to manage the stream using the

appropriate class. That is to say, the class ofstream is used to create

the output stream and the class ifstream to create the input stream.

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2. Initialize the file object with the desired file

For example, the following statement opens a file named

“results” for output

ofstream outfile(“results”);

Opening Files using open ():

The function open() can be used to open multiple files that use

the same stream object. There are two forms for open() method

With One argument:

File-stream-class stream-object;

Stream-object.open(“filename”);

Ex:ifstream fin;

With two arguments:

Stream-object.open(“filename”,mode);

File mode parameters:

Parameter Meaning

ios::in opening file for reading only

ios::out opening file for writing only

Detecting end of file:

Detecting end-of-file is necessary for preventing any further

attempt to read the data from the file. We can use the following

methods for detecting the end of the file

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By using while loop for ex:while(fin)\

By using the method eof() for

ex:

if(fin1.eof()!=0)

{

exit(1);

}

eof() is a member function of ios class. It returns a non-zero

value if the end of the file is encountered and a zero otherwise.

Fail() This method returns true when an input or output operation has

failed

READ() AND WRITE(): To read and write the class objects onto the file

we have to use the methods read() and write() and its syntax is

Infile.read((char *)&v, sizeof(v));

Outfile.write((char *)&v,sizeof(v));

The above two functions will take two arguments

1. Address of the variable

2. Size of the variable

ios::in Open for input operations.

ios::out Open for output operations.

ios::binar

y Open in binary mode.

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ios::ate

Set the initial position at the end of the file.

If this flag is not set to any value, the initial position is the

beginning of the file.

ios::app

All output operations are performed at the end of the file,

appending the content to the current content of the file. This

flag can only be used in streams open for output-only

operations.

ios::trunc

If the file opened for output operations already existed

before, its previous content is deleted and replaced by the

new one.

All these flags can be combined using the bitwise operator OR (|). For example, if

we want to open the file example.bin in binary mode to add data we could do it

by the following call to member function open():

ofstream myfile;

myfile.open ("example.bin", ios::out | ios::app |

ios::binary);

Each one of the open() member functions of the classes ofstream, ifstream and

fstream has a default mode that is used if the file is opened without a second

argument:

class default mode parameter

ofstream ios::out

ifstream ios::in

fstream ios::in | ios::out

For ifstream and ofstream classes, ios::in and ios::out are automatically and

respectivelly assumed, even if a mode that does not include them is passed as

second argument to the open() member function.

The default value is only applied if the function is called without specifying any

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value for the mode parameter. If the function is called with any value in that

parameter the default mode is overridden, not combined.

File streams opened in binary mode perform input and output operations

independently of any format considerations. Non-binary files are known as text

files, and some translations may occur due to formatting of some special

characters (like newline and carriage return characters).

Since the first task that is performed on a file stream object is generally to open

a file, these three classes include a constructor that automatically calls the

open() member function and has the exact same parameters as this member.

Therefor, we could also have declared the previous myfile object and conducted

the same opening operation in our previous example by writing:

ofstream myfile ("example.bin", ios::out | ios::app |

ios::binary);

Combining object construction and stream opening in a single

statement. Both forms to open a file are valid and equivalent.

Templates

Templates in one the important features of C++ which enables

us to create generic programming. It is an approach where generic

types are used as parameters in algorithms so that they work for a

variety of suitable data types and data structures. It can be considered

as a kind of macro. They are also called as ‘parameterized classes or

functions’.

We can define templates for both classes and functions. A

template can be used to create a family of classes or functions. A

template can be contributed as a kind of macro. When an object of a

specific type is defined for actual use, the template definition for that

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class is substituted with the required data type. Since a template is

defined with a parameter that would be replaced by the specified data

type at the time of actual use of the class or function, the templates

are some times called parameterized classes or functions.

The class template definition is very similar to an ordinary class

definition except the prefix 'template <class T>' and the use of type T.

This prefix tells the compiler that we are going to declare a template

and use T as a type name in the declaration.

The general format for class template is

template <class T> class classname

{

class member specification with anonymous type T

wherever appropriate

}

The general format for template function

template <class T> return_type function_name (arguments of type T)

{

body of function

}

Example Program for Template Function.


# include <conio.h>

template<class A>

A add(A x,A y)

{

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return x+y;

}

void main()

{

int m,n;

float f,p;

long l,r;

clrscr();

cout<<"ENTER TWO INTERGER :"<<endl;

cin>>m>>n;

cout<<"ENTER TWO FLOATS :"<<endl;

cin>>f>>p;

cout<<"ENTER TWO LONGS :"<<endl;

cin>>l>>r;

cout<<"FIRST INTEGER IS :"<<m<<endl;

cout<<"SECOND INTEGER IS :"<<n<<endl;

cout<<"FIRST FLOAT IS :"<<f<<endl;

cout<<"SECOND FLOAT IS :"<<p<<endl;

cout<<"FIRST LONG IS :"<<l<<endl;

cout<<"SECOND LONG IS :"<<r<<endl;

cout<<"SUM OF INTEGERS IS :"<<add(m,n)<<endl;

cout<<"SUM OF FLOATS IS :"<<add(f,p)<<endl;

cout<<"SUM OF LONGS IS :"<<add(l,r)<<endl;

getch();

}

Example Program to Template Functions with Multiple Templates.


# include <stdio.h>

# include <conio.h>

template<class A,class B>

A add (A x,B y)

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{

return(x+y);

}

void main()

{

int m;

float f;

long l;

clrscr();

cout<<"ENTER AN INTEGER :"<<endl;

cin>>m;

cout<<"ENTER A FLOAT VALUE :"<<endl;

cin>>f;

cout<<"ENTER A LONG VALUE :"<<endl;

cin>>l;

clrscr();

cout<<"INTEGER VALUE IS :"<<m<<endl;

cout<<"FLOAT VALUE IS :"<<f<<endl;

cout<<"LONG VALUE IS :"<<l<<endl;

cout<<"SUM OF INTEGER AND FLOAT VALUE IS :"<<add(m,f)<<endl;

cout<<"SUM OF FLOAT AND INTEGER VALUE IS :"<<add(f,m)<<endl;

cout<<"SUM OF LONG AND FLOAT VALUE IS :"<<add(l,f)<<endl;

cout<<"SUM OF LONG AND INTEGER VALUE IS :"<<add(l,m)<<endl;

getch();

}

Example Program for Class Templates.


# include <conio.h>

template<class A>

class sample

{

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A n,m,f;

public:

void input()

{

cout<<"ENTER FIRST VALUE :";

cin>>n;

cout<<"ENTER SECOND VALUE :";

cin>>m;

cout<<"ENTER THIRD VALUE :";

cin>>f;

}

A total()

{

return(n+m+f);

}

void output()

{

cout<<"FIRST VALUE IS :"<<n<<endl;

cout<<"SECOND VALUE IS :"<<m<<endl;

cout<<"THIRD VALUE IS :"<<f<<endl;

}

};

void main()

{

sample <int> T1; //object declared with integer members

sample <float> T2; //object declared with float members

sample <long> T3; //object declared with long members

clrscr();

cout<<"ENTER INTEGER VALUES :"<<endl;

T1.input();

cout<<"ENTER FLOAT VALUES :"<<endl;

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T2.input();

cout<<"ENTER LONG VALUES :"<<endl;

T3.input();

clrscr();

cout<<endl<<"INTEGER VALUES ARE :"<<endl;

T1.output();

cout<<"TOTAL VALUE IS :"<<T1.total()<<endl;

cout<<endl<<"FLOAT VALUES ARE :"<<endl;

T2.output();


cout<<endl<<"LONG VALUES ARE :"<<endl;

T3.output();


getch();

}

Date post:	27-Jan-2015
Category:	Education
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