File Handling in C

 Library Functions for Reading/Writing from/to a File

A. String Input/ Output

Using string i/O function, data can be read from a file or written to a file in the form of array of characters.

i. fgets():

It is used to read string from file.

fgets(string_ variable, int_ value, file_ ptr_ variable);

ii. fputs():

It is used to write a string to a file.

fputs(string, file_ ptr_ variable);

Example

Write a program to open the file “test.txt ” created , read its content and display to the screen.

#include<stdio.h>
 int main()
     { 
       FILE *fptr;
       char s[100];
      fptr=fopen ("c:\\test.txt","r");
       if(fptr==NULL)
           
        {
               printf("\nFile can not be opend");
                   exit(1);
             }
          fgets(s, 100, fptr);
         printf("The text from file is:\t%s",s);
         fclose(fptr);
          getch();
          return 0;
        }


  Output
       The text from file is: Welcome to my college

B. Character Input/ Output

Using character I/O functions, data can be read from a file or written to a file one character at a time.

i. fgetc():

It is used to read a character to read a character from a file.

char_ variable=fgetc(file_ ptr_ variable);

ii. fputc():

It is used to write a character to a file.

fputc(character or char_ variable, file_ ptr_ variable);

Example

Write a program to create file and write some text to it writing one character at a time using fputc() function. The program should write until hits enter key. Read filename from user.

#include<stdio.h>
 int main()
     {
       FILE *fptr;
       char c;
      char fileName [20];
       printf("Enter the name of file");
       scanf("%s", &fileName);
      fptr=fopen(fileName,"w");
    if(fptr=NULL)
  {
    printf("File can not be created");
    exit(0);
    }
      printf("Enter Text. Hit enter key to stop writing");
        fflush(stdin);
       while(c=getchar())!='\n')
      {
           fputc(c.fptr);
        }
          fclose(fptr);
      return 0;
  }


  Output
Enter the name of file: c:\student.dat
Enter Text. Hit enter key to.stop writing

This is example which reads some text from keyword character by character and stores in a file student.dat in c:\drive.

C. Formatted Input/ Output

These functions are used to read numbers, character or string from a file or write them to a file in format as our requirement.

i. fprintf():

It is formatted output function which is used to write integer , float, char or string data to a file.

fprintf(file_ ptr_ variable,"control_ string",&list_ variable);

ii. fscanf():

It is formatted input function which is used to read integer, float, char or string value from a file.

fscanf(file_ ptr_ variable, "controle_ string", &list_ variables);

Example

Write a program to create a file named student.txt in D:\ drive and write name, roll, address and marks of a student to the file.

 #include<stdio.h>
 int main()
 {
   FILE *f;
  char name [20], address[20];
    int roll;
   float marks;
  f=fopen("d:\student.txt","w");
  if(f=NULL)
  {
     printf("File can not be created!!!");
     exit(1);
    }
    
 printf("\Enter name of student :t");
 gets(name);
 printf("Enter roll number");
  scanf("%d",&roll);
  fflush(stdin);
  printf("Enter address of student ");
  gets(adress);
   printf("Enter marks of the student");
  scanf("%f", &marks);
  printf("The data is being written in file.....");
 fprintf(f,"Name=%s\nRoll=%d\naddress=%s\nmarks=%.2f",name,roll,address,marks);
   fclose(f);
   getch();
   return 0;
    }

Output
   Enter name of student: Ram pd sharam
   Enter roll number:      1001
   Enter address of student : Kathmandu
   Enter marks of the student: 89.5
   The data is being written in file...........

Binary Data Files

The binary files organize data into blocks containing contiguous  bytes of information. The binary files are recognized as a stream of bytes and programming languages tend to work with streams rather than files. In binary file, the opening mode of text mode file is appended by a character ‘b’ .

Example

Write a C program to write some text “welcome to my college” to a data file  in binary mode. Read its content and display it.

#include<stdio.h>
 int main()
  {
    FILE *fptr;
     char c;
   fptr=fopen ("test.txt", "w+b");
   if(fptr==NULL)
 {
   printf("File can not be created");
  }
 fputs("Welcome to my College",fptr);
     rewind(fptr);
 printf("The content from file");
 while((c=fgetc(fptr))!=EOF)
 {
   printf("%c",c);
   }
     fclose(fptr);
  return 0;
  }

  
      Ouptput
               The content from file:
                Welcome to my college