File Handling

November 01, 2020

File

File is a collection of bytes that is stored on secondary storage devices like disk. There are two kinds of files in a system. They are:

Text Files - contain ASCII codes of digits, alphabetic and symbols.
Binary Files - contains collection of bytes (0’s and 1’s). These are compiled version of text files.

File Handling Functions

SL.No	Function	Description
1	fopen()	opens a file to perform operations such as reading, writing etc.
2	fclose()	closes the file that is being pointed by file pointer fp.
3	fgets()	reads a file line by line.
4	fprintf()	writes string into a file pointed by fp.

Mode Of Operation Performed On A File

SL.No	Modes	Description
1	r	opens a file in read mode and sets pointer to the first character in the file. It returns null if file does not exist.
2	w	opens a file in write mode. It returns null if file could not be opened. If file exists, data are overwritten.
3	a	opens a file in append mode. It returns null if file couldn’t be opened.
4	r+	opens a file for read and write mode and sets pointer to the first character in the file.
5	w+	opens a file for read and write mode and sets pointer to the first character in the file.
6	a+	opens a file for read and write mode and sets pointer to the first character in the file. But, it can’t modify existing contents.

//Opening a file in read mode
#include<stdio.h>
#include<string.h>
int main()
{
	FILE *fp ;
	char dataToBeRead[50];
	// Open the existing file using fopen() in read mode using "r" attribute
	fp = fopen("file.txt", "r") ;
	// Check if this filePointer is null which maybe if the file does not exist
	if ( fp == NULL )
	{
		printf( "Failed to open the file." ) ;
	}
	else
	{
		// Read the dataToBeRead from the file using fgets() method
		while( fgets (dataToBeRead, 50, fp) != NULL )
		{
			if(ferror){
				perror(fp);

			}
			fseek(fp,2-4,SEEK_END);
			// Print the dataToBeRead
			printf("%s",dataToBeRead);
		}
		// Closing the file using fclose()
		fclose(fp) ;
	}
	return 0;
}

//Program to Write on Data File and Read From Data File
#include<stdio.h>

struct Student {
   int roll;
   char name[12];
   int percent;
} s1 = { 1, "Anushka Raj", 82 };

int main() {
   FILE *fp;
   struct Student s2;

   //Write details of s1 to file
   fp = fopen("ip.txt", "w");
   fwrite(&s1, sizeof(s1), 1, fp);
   fclose(fp);

   fp = fopen("ip.txt", "r");
   fread(&s2, sizeof(s2), 1, fp);
   fclose(fp);

   printf("\nRoll : %d", s2.roll);
   printf("\nName : %s", s2.name);
   printf("\nPercent : %d", s2.percent);

   return (0);
}