6.18.13 ferror Function

Tests if error indicator is set.

Include

<stdio.h>

Prototype

int ferror(FILE * stream);

Argument

stream

pointer to FILE structure

Return Value

Returns a non-zero value if error indicator is set; otherwise, returns a zero.

Example

See the notes at the beginning of this chapter or section for information on using printf() or scanf() (and other functions reading and writing the stdin or stdout streams) in the example code.

/* This program tries to write to a file that is */
/* readonly. This causes the error indicator to  */
/* be set.  The function ferror is used to check */
/* the error indicator and find the error. The   */
/* function clearerr is used to reset the error  */
/* indicator so the next time ferror is called   */
/* it will not report an error.                  */

#include <stdio.h>

int main(void)
{
  FILE *myfile;

  if ((myfile = fopen("sampclearerr.c", "r")) == NULL)
    printf("Cannot open file\n");
  else
  {
    fprintf(myfile, "Write this line to the file.\n");
    if (ferror(myfile))
      printf("Error\n");
    else
      printf("No error\n");
    clearerr(myfile);
    if (ferror(myfile))
      printf("Still has Error\n");
    else
      printf("Error indicator reset\n");

    fclose(myfile);
  }
}

Example Output

Error
Error indicator reset