file_c.pdf

Why File Handling in C?
• Permanent Storage: File handling allows the program to
store data persistently.
• Data Sharing: File handling enables data to be shared
between different programs.
• Large Data: File handling is ideal for dealing with large
amounts of data.
• Data Backup: File handling provides a way to create backups
of important data. Dr Namita Parati

STREAMS IN C
• In C, the standard streams are termed as pre-connected input and output
channels between a text terminal and the program (when it begins
execution).Therefore, stream is a logical interface to the devices that are
connected to the computer.
• Stream is widely used as a logical interface to a file where a file can refer to
a disk file, the computer screen, keyboard, etc. Although files may differ in
the form and capabilities, all streams are the same.
• The three standard streams in C languages are-
• standard input (stdin), standard output (stdout) and standard
error (stderr).
Dr Namita Parati

STREAMS IN C contd.
• Standard input (stdin): Standard input is the stream from which the program
receives its data. The program requests transfer of data using the read
operation. However, not all programs require input. Generally, unless
redirected, input for a program is expected from the keyboard.
• Standard output (stdout): Standard output is the stream where a program
writes its output data. The program requests data transfer using the write
operation. However, not all programs generate output.
• Standard error (stderr): Standard error is basically an output stream used by
programs to report error messages or diagnostics. It is a stream independent of
standard output and can be redirected separately. No doubt, the standard
output and standard error can also be directed to the same destination.
• A stream is linked to a file using an open operation and disassociated
from a file using a close operation.
KEYBOARD
PROGRAM
SCREEN
stdin
stderr
stdout
Dr Namita Parati

BUFFER ASSOCIATED WITH FILE STREAM
• When a stream linked to a disk file is created, a buffer is automatically created and associated with the stream. A buffer is
nothing but a block of memory that is used for temporary storage of data that has to be read from or written to a file.
• Buffers are needed because disk drives are block oriented devices as they can operate efficiently when data has to be
read/ written in blocks of certain size. The size of ideal buffer size is hardware dependant.
• The buffer acts as an interface between the stream (which is character-oriented) and the disk hardware (which is block
oriented). When the program has to write data to the stream, it is saved in the buffer till it is full. Then the entire contents
of the buffer are written to the disk as a block.
PROGRAM
BUFFER DISK
Program writes data to buffer
Data from the buffer is written to the disk file
Similarly, when reading data from a disk file, the data is read as a block from the file and written into
the buffer. The program reads data from the buffer. The creation and operation of the buffer is
automatically handled by the operating system. However, C provides some functions for buffer
manipulation. The data resides in the buffer until the buffer is flushed or written to a file.
Dr Namita Parati

Difference between Text File and Binary File
Text File Binary File
It contains alphabets and numbers which
are easily understood by human beings.
It contains 1’s and 0’s, which are easily
understood by computers.
An error in a text file can be eliminated
when seen.
The error in a binary file corrupts the file
and is not easy to detect.
Can store only plain text in a file.
Can store different types of data (image,
audio, text) in a single file.
Widely used file format and can be
opened using any simple text editor.
Developed especially for an application
and may not be understood by other
applications.
Mostly .txt is used as extensions to text
files.
Can have any application defined
extension.
Dr Namita Parati

Files can be accessed in 2 ways
• Sequential Access
It is the simplest access method. Information in the file is processed
in order, one after the other.
• Direct Access (Random Access)
Another method is direct access method also known as relative access
method.
A filed-length logical record that allows the program to read and
write record randomly in no particular order.
Dr Namita Parati

Sequential Versus Random Access
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File handling operations
• File handling in C allows us to create, update, read, and delete the
files stored on the local file system through our C program.
• The following operations can be performed on a file.
• Creation of the new file
• Opening an existing file
• Reading from the file
• Writing to the file
• Deleting the file
Dr Namita Parati

Functions for file handling
No. Function Description
1 fopen() opens new or existing file
2 fprintf() write data into the file
3 fscanf() reads data from the file
4 fputc() writes a character into the file
5 fgetc() reads a character from file
6 fputs() writes a string to file
7 fgets() reads a string from file
8 fclose() closes the file
9 fseek() sets the file pointer to given position
10 ftell() returns current position
11 rewind() sets the file pointer to the beginning of the file
Dr Namita Parati

Sequential Access Functions
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Random Access Functions
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Opening File: fopen()
• We must open a file before it can be read, write, or update.
• The fopen() function is used to open a file.
• The syntax of the fopen() is given below.
• FILE *fopen( const char * filename, const char * mode );
Dr Namita Parati

• The fopen() function accepts two parameters:
• The file name (string). If the file is stored at some specific
location, then we must mention the path at which the file is
stored. For example, a file name can be
like "c://some_folder/some_file.ext".
• The mode in which the file is to be opened. It is a string.
Dr Namita Parati

We can use one of the following modes in the fopen() function.
Mode Description
r opens a text file in read mode
w opens a text file in write mode
a opens a text file in append mode
r+ opens a text file in read and write mode
w+ opens a text file in read and write mode
a+ opens a text file in read and write mode
rb opens a binary file in read mode
wb opens a binary file in write mode
ab opens a binary file in append mode
rb+ opens a binary file in read and write mode
wb+ opens a binary file in read and write mode
ab+ opens a binary file in read and write mode
Dr Namita Parati

The fopen function works in the following way.
• Firstly, It searches the file to be opened.
• Then, it loads the file from the disk and place it into the buffer. The
buffer is used to provide efficiency for the read operations.
• It sets up a character pointer which points to the first character of the
file.
Dr Namita Parati

fopen() example
// C program to illustrate fopen()
#include <stdio.h>
#include <stdlib.h>
main()
{
// pointer demo to FILE
FILE* fp;
// Creates a file "demo_file"
// with file acccess as write-plus mode
fp = fopen("demo_file.txt", "w+");
// adds content to the file
fprintf(demo, "%s %s %s", "Welcome", "to", “MVSR");
// closes the file pointed by fp
fclose(fp);
}
a new file will be created by the
name “demo_file” and with the
following content:
Welcome to MVSR
Dr Namita Parati

Example2 Reading Char by Char from a file
#include<stdio.h>
void main( )
{
FILE *fp ;
char ch ;
fp = fopen(“hello.c","r") ; //use existing file name
while ( 1 )
{
ch = fgetc ( fp ) ;
if ( ch == EOF )
break ;
printf("%c",ch) ;
}
fclose (fp ) ;
}
Dr Namita Parati

Closing File: fclose()
• The fclose() function is used to close a file. The file must be closed
after performing all the operations on it.
• The syntax of fclose() function is given below:
• int fclose( FILE *fp );
Dr Namita Parati

fprintf() function
• The fprintf() function is used to write set of characters into
file. It sends formatted output to a stream.
#include <stdio.h>
main(){
FILE *fp;
fp = fopen("file.txt", "w");//opening file
fprintf(fp, "Hello file by fprintf...n");//writing data into file
fclose(fp);//closing file
}
Dr Namita Parati

fscanf() function
• The fscanf() function is used to read set of characters from file.
• It reads a word from the file and returns EOF at the end of file.
#include <stdio.h>
main(){
FILE *fp;
char buff[255];//creating char array to store data of file
fp = fopen("file.txt", "r");
while(fscanf(fp, "%s", buff)!=EOF){
printf("%s ", buff );
}
fclose(fp);
}
Output:
Hello file by fprintf...
Dr Namita Parati

C File Example: Storing employee information
• file handling example to store employee information as entered by user from console.
• We are going to store id, name and salary of the employee.
#include <stdio.h>
void main()
{
FILE *fptr;
int id;
char name[30];
float salary;
fptr = fopen("emp.txt", "w+");/* open for writing */
if (fptr == NULL)
{
printf("File does not exists n");
return;
}
Dr Namita Parati

printf("Enter the idn");
scanf("%d", &id);
fprintf(fptr, "Id= %dn", id);
printf("Enter the name n");
scanf("%s", name);
fprintf(fptr, "Name= %sn", name);
printf("Enter the salaryn");
scanf("%f", &salary);
fprintf(fptr, "Salary= %.2fn", salary);
fclose(fptr);
}
Output:
Enter the id 1
Enter the name Ravi
Enter the salary
120000
Dr Namita Parati

Now open file from current directory.
you will see emp.txt file. It will have following
information.
emp.txt
Id= 1 Name= Ravi Salary= 120000
Dr Namita Parati

fputc() function
• The fputc() function is used to write a single character into file.
• It outputs a character to a stream.
#include <stdio.h>
main(){
FILE *fp;
fp = fopen("file1.txt", "w");//opening file
fputc('a',fp);//writing single character into file
fclose(fp);//closing file
}
file1.txt
a
Dr Namita Parati

fgetc() function
• The fgetc() function returns a single character from the file.
• It gets a character from the stream. It returns EOF at the end of file.
#include<stdio.h>
void main(){
FILE *fp;
char c;
fp=fopen("myfile.txt","r");
while((c=fgetc(fp))!=EOF)
{
printf("%c",c);
}
fclose(fp);
}
Dr Namita Parati

fputs() function
• The fputs() function writes a line of characters into file. It outputs
string to a stream.
#include<stdio.h>
void main(){
FILE *fp;
fp=fopen("myfile2.txt","w");
fputs("hello c programming",fp);
fclose(fp);
}
Dr Namita Parati

fgets() function
• The fgets() function reads a line of characters from file. It gets string
from a stream.
#include<stdio.h>
void main(){
FILE *fp;
char text[300];
fp=fopen("myfile2.txt","r");
printf("%s",fgets(text,200,fp));
fclose(fp);
}
Dr Namita Parati

fseek() function
• The fseek() function is used to set the file pointer to the specified
offset(address). It is used to write data into file at desired location.
#include <stdio.h>
void main(){
FILE *fp;
fp = fopen("myfile.txt","w+");
fputs("This is last unit", fp);
fseek( fp, 7, SEEK_SET );
fputs(“important", fp);
fclose(fp);
}
myfile.txt
This is important
Dr Namita Parati

rewind() function
• The rewind() function sets the file pointer at the beginning of the
stream. It is useful if you have to use stream many times.
#include<stdio.h>
void main(){
FILE *fp;
char c;
fp=fopen("file.txt","r");
Dr Namita Parati

while((c=fgetc(fp))!=EOF){
printf("%c",c);
}
rewind(fp);//moves the file pointer at beginning of the file
while((c=fgetc(fp))!=EOF){
printf("%c",c);
}
fclose(fp);
}
Output:
this is a simple textthis is a simple
text
Dr Namita Parati

ftell() function
• The ftell() function returns the current file position of the specified stream.
We can use ftell() function to get the total size of a file after moving file
pointer at the end of file.
#include <stdio.h>
void main (){
FILE *fp;
int length;
clrscr();
fp = fopen("file.txt", "r");
fseek(fp, 0, SEEK_END);
length = ftell(fp);
fclose(fp);
printf("Size of file: %d bytes", length);
}
Output:
Size of file: 21 bytes
Dr Namita Parati

C program to copy the contents of one file to another file
#include <iostream>
#include <stdlib.h>
int main() {
char ch;// source_file[20], target_file[20];
FILE *source, *target;
char source_file[]="x1.txt";
char target_file[]="x2.txt";
source = fopen(source_file, "r");
if (source == NULL) {
printf("Press any key to exit...n");
exit(EXIT_FAILURE);
}
target = fopen(target_file, "w");
if (target == NULL) {
fclose(source);
printf("Press any key to exit...n");
exit(EXIT_FAILURE);
}
while ((ch = fgetc(source)) != EOF)
fputc(ch, target);
printf("File copied successfully.n");
fclose(source);
fclose(target);
return 0;
}
Dr Namita Parati

Merging the contents of two files
#include<stdio.h>
main()
{
FILE *fp,*fp1,*fp2;
int i;
char ch;
fp=fopen("mfile.txt","a");
if(fp==NULL)
{
printf("File could not be openedn");
exit(0);
}
fp1=fopen("file1.txt","r");
if(fp1==NULL)
{
exit(0);
}
while((ch=fgetc(fp1))!=EOF)
fputc(ch,fp);
fputc('n',fp);
fp2=fopen("file2.txt","r");
if(fp2==NULL)
{
exit(0);
}
while((ch=fgetc(fp2))!=EOF)
fputc(ch,fp);
fclose(fp2);
fclose(fp1);
fclose(fp);
}
Dr Namita Parati

Command Line arguments
Dr Namita Parati

file_c.pdf

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