Aae oop xp_12

File Input and Output

Objectives
In this lesson, you will learn to:
Define the stream class hierarchy
Identify the stream insertion and extraction operators
Use the stream classes for file input and output
Differentiate between text and binary file input and
output
Apply the following functions for opening and closing
files:
open()
close()

©NIIT OOPS/Lesson 12/Slide 1 of 36


Objectives (Contd.)
Use the open mode bits
Randomly access data files



Stream Class Hierarchy

System-Defined
ios
Streams

istream ostream

iostream

User-Defined
ifstream fstream ofstream Streams



Features of Stream Classes
Stream Classes:
Form a powerful set of classes that can be modified,
extended, or expanded to incorporate user-defined
data types or classes
Are fully buffered to reduce disk access
Encapsulate their internal working from the user
Offer a rich set of error-handling facilities



Stream Insertions
Are output operations for which the functions are
defined in the ostream class



Stream Insertion Operators
Are defined in the ostream class
The operator “” is called the inserter



Stream Extractions
Are input operations for which the functions are
defined in the istream class



Stream Extraction Operators
Are defined in the istream class and are used to
receive data from the input device
The operator “”, called the extractor, accepts any
built-in data type passed as arguments



The get() and getline() Functions
Are used to read a complete string from the input
stream
Recognize white spaces
The get() function
Syntax:
cin.get(char *str, int len, char delim =
'n');
The getline() function
Syntax:
cin.getline(char *str, int len, char
delim = 'n');



Problem Statement 10.D.1
Write an application that will accept input from the user
by using the get() function until the input from the
keyboard is “N” or nine characters depending on
whichever is first.



File Input and Output Using Built-in Data Types
Integer Input and Output
Example:
#include fstream
int main()
{
ofstream outobj(INT.TST);
outobj 25 ' ' 4567 ' '
8910;
return 0;
}


File Input and Output Using Built-in Data Types
(Contd.)
Character input and output
Example:
#include fstream
int main()
{
ofstream out(STR.TST);
out This is a test string;
return 0;
}


File Input and Output Using Objects
Example:
#includefstream.h
class student
{
private:
int iReg_no;char cName[20];
public:
void setRegno();
void setName();
int getRegno();
char *getName();
};



File Input and Output Using Objects (Contd.)
void main()
{
ofstream Sfil(“studfile.dat”);
char ch;
student Svar;
Svar.setRegno();
Svar.setName();
SfilSvar.getRegno()
“ ”Svar.getName();
Sfil.close(); //Closes the open file



File Input and Output Using Objects (Contd.)
cout “n Do you want to view the
contents of a file (y/n)?”;
cinch;
if(ch== ‘y’)
{
ifstream Sfil(“studfile.dat”);
char ireg;char nam[20];
Sfiliregnam;
cout“n Registration Number is ”
ireg;
cout“n Student Name is ” nam;
}
}


Binary Input and Output
Character input and output
The put() function
Syntax:
[object_of_ofstream].put(character_variable);
The get() function
Syntax:
[object_of_ifstream].get(character_variable);
Integer input and output
The read function
Syntax:
read(char* addr, int size)


Binary Input and Output (Contd.)
The write function
Syntax:
write(char* addr, int size)
File input and output using abstract data types
read() and write() functions are used to read
or write user-defined objects on a file



The open() Function
Is used to open a file
Example:
ifstream Ifil; //creates an
//unopened input stream
Ifil.open(DATA.DAT); //associates
//the stream to a file



The close() Function
Is used to close a file
Example:
ofstream Ofil;
Ofil.open(DATA.DAT);
...
...
Ofil.close();



As part of the customer tracking system for Diaz
Telecommunication, Inc., an application is to be created
that can:
Accept customer details
Save the customer details in a file
Display the details of existing customers



Problem Statement 10.P.1
As part of the reservation system for the Northern
Railways, an application is to be created that:
Accepts passenger details
Saves passenger details in a file
Displays the details of the passengers who have
confirmed bookings



Open Mode Bits
Are defined in the ios class
Are bits that are associated with the opening of files
Represent the mode in which the file is opened



Open Mode Bits (Contd.)

Mode Explanation

app Starts reading or writing at the end of the file. Does not have a
meaning with input streams, it is used only for output streams
in Open for reading
out Open for writing
ate Seek to the end of the file
trunc If the file exists, it is truncated, i.e. all data is erased before
writing/reading



The get Pointer
Specifies the location in the file where the next read
operation will occur



The put Pointer
Specifies the location in the file where the next write
operation will occur



The seekg() Function
Helps to control the get pointer
Moves the get pointer to an absolute address within
the file or to a certain number of bytes from a
particular position
Takes two arguments:
The number of bytes to move

The reference in the file from where the pointer
has to be repositioned
Example:
ifstream iFil;
iFil.seekg(10,ios::beg);


The tellg() Function
Helps to control the get pointer
Can be used to find the current position of the get file
pointer in a file
Does not take any arguments
Example:
int
iPosition=iFil.tellg();



The seekp() Function
Helps to control the put pointer
Moves the put pointer to an absolute address within
the file or to a certain number of bytes from a
particular position



The tellp() Function
Helps to control the put pointer
Can be used to find the current position of the put file
pointer in a file



Write an application that reads the contents of any
existing text file in reverse order.



Problem Statement 10.P.2
Modify the Northern Railway application defined in
10.P.1 for the user to:
Query the passenger details based on PNR Number
Modify the booking status, if the reservation is
cancelled



Summary
In this lesson, you learned that:
The information can be saved permanently on the disk
using either flat-files or a database
A file has two components:
Fields
Records
A field is the smallest unit of data that contains only
one type of data
A record is a collection of all the fields that present
information for a single entity uniquely identified by a
key


Summary (Contd.)
The file is also defined as a stream of characters or a
flow of related data and are two kinds:
Output streams, which allow you to write or store
characters
Input streams, which allow you to read or fetch
characters
The stream class consists mainly of the following
classes:
ios
istream
ostream


Summary (Contd.)
iostream
ifstream
ofstream
fstream
Inserters and extractors do not recognize white
spaces
Inserters and extractors can be used for both input
and output of all the built-in and user-defined objects
File streams consists of their own constructors and
destructors



Summary (Contd.)
File streams consists of the open() and
close()member functions
Binary input and output is supported by the following
stream class member functions:
get()
put()
getline()
read()
write()



Summary (Contd.)
The C++ - I/O system manages two integer values
associated with file positions:
The get pointer
The put pointer
Random access of data files can be done using the
seekg() and seekp() member functions
The current positions of the get and put pointers in a
file can be found by the tellg() and tellp()
functions, respectively


Aae oop xp_12

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