What are the error handling techniques in C language?

Some of the errors that occurs in the files are listed below −

• Trying to read beyond end of file.
• Device over flow.
• Trying to open an invalid file.
• An invalid operation is performed by opening a file in a different mode.

Functions for error handling

The functions for error handling are as follows −

• ferror ( )
• perror ( )
• feof ( )

ferror ( )

It is for detecting an error while performing read or write operations.

The syntax is as follows −

int ferror (file pointer);

For example,

FILE *fp;
if (ferror (fp))
printf ("error has occurred”);

It returns zero, if it is a success and returns as non-zero in other cases.

perror ( )

It is used for printing an error.

It shows the string that pass to it, which is followed by a colon, a space, and the text representation of current error value.

The syntax is as follows −

perror (string variable);

For example,

FILE *fp;
char str[30] = ”Error is”;
perror (str);

Output

Error is: error 0

Exaple

Following is the C program for usage of ferror ( ) and perror ( ) function −

#include<stdio.h>
main ( ){
   FILE *fp;
   char str[30] = "error is";
   int i = 20;
   clrscr ( );
   fp = fopen ("sample. txt", "r");
   if (fp = = NULL){
      printf ("file doesnot exist");
   } else {
      fprintf (fp, "%d", i);
      if (ferror (fp)){
         perror (str);
         printf ("error ");
   }
   fclose (fp);
   getch ( );
}

Output

When the above program is executed, it produces the following result −

Error is: Error1 compiler generated.
Error.

feof ( )

It is used for checking whether an end of the file has been reached or not.

The syntax is as follows −

int feof ( file pointer);

For example,

FILE *fp;
if (feof (fp))
printf ("reached end of the file");

If it returns a non-zero then, it is success. Otherwise, it is zero.

Example

Following is the C program for usage of feof ( ) function −

#include<stdio.h>
main ( ){
   FILE *fp;
   int i,n;
   clrscr ( );
   fp = fopen ("number. txt", "w");
   for (i=0; i<=100;i= i+10){
      putw (i, fp);
   }
   fclose (fp);
   fp = fopen ("number. txt", "r");
   printf ("file content is”);
   for (i=0; i<=100; i++){
      n = getw (fp);
      if (feof (fp)){
         printf ("reached end of file");
         break;
      }
      else{
         printf ("%d", n);
      }
   }
   fclose (fp);
   getch ( );
}

Output

When the above program is executed, it produces the following result −

File content is
10 20 30 40 50
60 70 80 90 100
Reached end of the file.