Chapter - 9, File Handling, HSSC-II (12th Class) Computer Science Key Point Notes,

12th Class (HSSC-II) Computer SLO Based Key Point Notes

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Based on National Curriculum Pakistan 2023-2024 and Onward prescribed by Federal Board of Intermediate and Secondary Education, Islamabad, and All Pakistan Boards)

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Unit 9: File Handling

9.1. Introduction to File Handling

Sometimes we need large data to process.
It will be more convenient to process those data if stored on secondary memory such as a hard disk.
Once the data is stored on a hard disk, it can be used as many times as needed without being reentered from the keyboard.
Also, data can be processed by a program and the output produced by the program can be stored on secondary memory which will be used later on.
C language provides the facilities for the input and output of the data to a disk.

File

A file is a collection of data or bytes stored on the disk that is given a name.
The bytes of the file are interpreted in different ways for example:

A text document interprets the bytes as characters, words, lines, paragraphs, or pages.
A graphical image may interpret the bytes as pixels.
A database interprets the bytes as fields and records.

The information regarding data structure of file and operations used to process the file is attached with each file.

File Handling:

The process of performing different operations on files is called file handling. It involves the following operations:

Opening file
Reading / Writing file
Closing file.

9.1.1 Types Of Files

1. Text File:

A type of file that stores data as readable and printable characters is called a text file.
The user can view, read, and print the text file.
It is a stream of characters that can be processed by a computer sequentially in the forward direction. That is why a text file is typically opened only for one type of operation at a time such as reading or writing etc.
Only one character can be read or written to the text files at a time.

2. Binary Files:

A type of file that stores data as non-readable binary code is called a binary file.
The user cannot read binary files. It can only be read and processed by computer.
The binary file can be processed using sequential or random access methods.
It can be opened for read and write operations at the same time.
For example, a database file is created and processed as a binary file. The process of updating a record will be performed as follows:

Locating the appropriate record.
Reading the record into memory.
Modifying the record as required.
Writing the updated record back to the file

9.1.2 Opening a File

A file can be opened by first creating an object of ifstream, ofstream, or fstream class that is known as a steam object which will be associated with a file.
Any input or output or both operations performed on this object are applied to the file associated with it.
The member function “open()” of the stream object is used to open a file that has the following syntax:

object_name.open( file name , mode );

Modes of opening a File:

A file can be opened in different modes using the open() function which indicates the type of operations to be performed on the file after opening.

The following are the different modes:

For example to open a file:

fstream obj;
obj.open(“abc.txt”, ios::out);

A file can be opened in multiple modes using OR operator i.e.:
fstream test;
test.open(“c:\\xyz.txt”, ios::out | ios::in);

Default opening Mode:

If the mode parameter is not used by the user in the open() member function, then the function uses default mode to open a file.

The default modes are given below:

Closing a File

The opened file should be closed when the input or output operations on the file are finished.
The member function close() of stream object is used to close a file which has the following syntax:

object_name.close();

For example:
test.close();
obj.close();

9.1.3 bof() and eof()

bof() function

The word bof stands for Beginning of File.
bof() function returns the value of bof pointer.
bof() function is used to find if the control is at the beginning of the file or not.
It returns TRUE if the control is at the beginning and returns FALSE otherwise.
The syntax of using bof() function is as follows:

object_name.bof();

eof() Function:

The word eof stands for End of File.
The eof() function returns the value of pointer.
The eof() function is used to find if the controls have reached the end of the file or not.
It returns TRUE if the control has reached the end of the file and returns FALSE otherwise.
The syntax of using eof() function is as follows:

object_name.eof();

Verifying File opening

• The stream object returns TRUE if the referred file is opened and returns FALSE if file not opened. For example:

fstream obj;
obj.open(“test.txt”, ios::in | ios::out );
if(obj)
cout<<“file is opened”;
else
cout<<“file is not opened”;

Example 1

• Write a program that creates a text file and writes a line of text in it.

#include <iostream.h>
#include <conio.h>
#include <fstream.h>
void main()
{
       clrscr();
       ofstream myfile;
       myfile.open(“d:\\new\\example1.txt”);
       myfile<<“Hello World”;
       myfile.close;
       getch();
};

The insertion operator << is used with a stream object to store data in a file. It is used in the same way as it is used with cout to display output on screen.

Example 2:

• Write a program that inputs the name of five cities and stores them in a file “city.txt”

#include <iostream.h>
#include <conio.h>
#include <fstream.h>
void main()
{
       clrscr();
       char city[20];
       ofstream file;
       file.open(“d:\\new\\city.txt”);
       for( int i=1; i<=5; i++)
       {
                   cout<<“Enter the city name: “;
                   cin>>city;
                   file<<city<<endl;
       }
       file.close;
       getch();
}

Reading from a file:

The extractor operator >> is used to read from a file.
It can read one word from the file at a time and store it in a variable or string.
The extractor operator needs to be used repeatedly to read all the contents in a file.

For example:

char ch[20];
ifstream obj;
obj.open(“abc.txt”);
obj>>ch;
cout<<ch;

Example 3:

• Write a program that displays all the records in the file city.txt

#include <iostream.h>
#include <conio.h>
#include <fstream.h>
void main()
{
       clrscr();
       char city[20];
       ifstream file;
       file.open(“d:\\new\\city.txt”);
       while(!file.eof())
       {
       file>>city;
                       cout<<city<<endl;
       }
       file.close;
       getch();
}

Reading / Writing files character by character

The data can be read from or written to a file character by character.
get() function is used to read a single character from a file.

The syntax for using this function is as under:

object_name.get(ch);

put() function is used to write a single character in a file. The syntax for using this function is as under:

object_name.put(ch);

Example:

• Write a program that inputs five characters from the user and stores them in a file.

#include <iostream.h>
#include <conio.h>
#include <fstream.h>
void main()
{
       clrscr();
       char ch;
       ofstream file;
       file.open(“d:\\new\\write.txt”);
       for( int i=1; i<=5; i++)
       {
                   cout<<“Enter a character: “;
                   cin>>ch;
                   file.put(ch);
       }
file.close;
getch();
}

Example:
• Write a program that reads the characters from a text file and displays them on screen.

#include <iostream.h>
#include <conio.h>
#include <fstream.h>
void main()
{

clrscr();
char ch;
ifstream file;
file.open(“d:\\new\\write.txt”);
while(!file.eof())
{

file.get(ch);
cout<<ch<<endl;

}
file.close;
getch();

}

9.1.4 Stream

In C++, a sequence of bytes/data associated with a file is called a stream. It consists of data that is exchanged between a file and the program.

9.1.5 Types of Streams

Two main types of streams in C++ are as follows:

1. Input Stream:

It is used to input data which takes a sequence of bytes/data from an input device such as a keyboard or file and enters it into a program.

2. Output Stream:

It is used to output data which sends a sequence of bytes/data from a file to an output device such as a monitor, file, or printer.

<fstream.h> Header file

It is a header file that contains classes and functions which are used in file handling.
To perform file processing or file handling in C++, <fstream.h> header file must be included in the C++ source program.

It consists of the following data types or classes:

1. ifstream:

• It is only used for input which creates the file reads information from files and enters into the program.
• It consists of the get() function, getline() function, etc. which are used to read the contents of the file.

2. ofstream:

It is only used for output which creates a file and writes information into a file.
It consists of the put() function, write() function, etc. which are used to write information into a file.

3. fstream:

It has the abilities of both ifstream and ofstream classes which means it can create files, write information to files, and read information from files.

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