File handling in C language

 

File Handling in C

File is permanent storage of data .It used to store output in files.

File handling in C enables 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

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Functions for file handling

There are many functions in the C library to open, read, write, search and close the file. A list of file functions are given below:

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	fclose()	closes the file
7	fseek()	sets the file pointer to given position
8	fputw()	writes an integer to file
9	fgetw()	reads an integer from file
10	ftell()	returns current position
11	rewind()	sets the file pointer to the beginning of the file
12	feof	Detects end-of-file marker in a file

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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  *fp;

The fopen() function accepts two parameters:

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

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WRITING A FILE

 

#include<stdio.h>

#include<conio.h>

main()

{

 

FILE *fp;

clrscr();

fp= fopen("sample.txt","w");

fputc('s',fp);

getch();

}

READING A FILE

#include<stdio.h>

#include<conio.h>

main()

{

char ch;

FILE *fp;

clrscr();

fp= fopen("sample.txt","r");

ch=fgetc(fp);

printf("%c",ch);

fclose(fp);

getch();

}

output

s

 

fprintf & fscanf function

#include<stdio.h>

#include<conio.h>

main()

{

    char name[40];

    int age,i;

    float bs;

    FILE *fp;

    clrscr();

    fp=fopen("employee.txt","w");

    if(fp==NULL)

    {

       printf("Cannot open file");

       exit();

    }

    for(i=0;i<5;i++)

    {

       printf("\n Enter Name , age , Salary\n");

       scanf("%s%d%f",&name,&age,&bs);

       fprintf(fp,"%s %d %f\n",name,age,bs);

    }

    fclose(fp);

}

 

#include<stdio.h>

#include<conio.h>

main()

{

   char name[40];

   int age,i;

   float bs;

   FILE *fp;

   clrscr();

   fp=fopen("employee.txt","r");

   if(fp==NULL)

   {

       printf("Cannot open file");

   }

 

 

       while(fscanf(fp,"%s %d %f",&name,&age,&bs)!=EOF)

       printf("%s %d %f\n",name,age,bs);

   fclose(fp);

   getch();

}

output

raja 20 1000.000000

somu 30 5000.000000

arun 35 6000.000000

hari 40 7000.000000

karthi 50 8000.000000

 

C fseek() function

The fseek() function is used to set the file pointer to the specified offset. It is used to write data into file at desired location.

int fseek(FILE *stream, long int offset, int whence)

Example:

#include <stdio.h> 

#include<conio.h>

 main(){ 

      FILE *fp; 

   fp = fopen("myfile.txt","w+");

   clrscr(); 

   fputs("welcome ", fp);  

   fseek( fp, 8, SEEK_SET ); 

   fputs("to the world", fp); 

   fclose(fp); 

} 

myfile.txt

welcome to the world

 

ftell() function

To create a file name myfile1.txt in turboc3 bin folder text file

 

#include<stdio.h>

#include<conio.h>

void main()

{

char fdata[50];

FILE *fstream = fopen("myfile1.txt","r");

clrscr();

printf("The current location of th pointer before reading from the file is : %ld\n", ftell(fstream));

fscanf(fstream,"%s",fdata);

printf("The current data read from the file is : %s\n", fdata);

printf("The current location of th pointer after reading from the file is : %ld\n", ftell(fstream));

getch();

}