tell Function

The tell function is used to find the current position of a file pointer.

Handle

Selector (file descriptor) of an open file.

>=0

Current number of bytes by which the file pointer is positioned from the origin..

-1

The seek failed.

errno

Iff the tell fails, the global variable errno is set to one of:

EBADF

Handle not open

#include <stdio.h>
#include <io.h> 
#include <fcntl.h>
#include <errno.h>

int main () {
  int Account_Master;
  char Buffer [100]; 
  int Maximum; 
  int Actual;
  /* Other declarations */
  Maximum = 100;
  Account_Master = open ("accounts.dat", O_RDWR);
  if (Account_Master >0) {
    printf ("Open succeeded.\n");
  } else {
    printf ("Open failed.\n")
    switch (errno) {
      case EACCES:  printf ("Permission denied.\n"); break;
      case EINVACC: printf ("Invalid access mode.\n"); break;
      case EMFILE:  printf ("No file handle available.\n"); break;
      case ENOENT:  printf ("File or path not found.\n"); break;
      default:      printf ("Unknown error.\n"); break;
    }
  /* File processing */
  while (!eof (Account_Master)) {
    Pos = tell (Account_Master);
    Actual = read (Account_Master, Buffer, Maximum);
    /* MODIFY THE RECORD */
    /* rewrite the record */
    lseek (Account_Master, Pos, SEEK_SET);
    Actual = write (Account_Master, Buffer, Maximum);
  }
  if (close (Account_Master) == 0) {
    printf ("Close succeeded.\n");
  } else {
    printf ("Close failed.\n")
    switch (errno) {
      case EBADF:  printf ("File not open.\n"); break;
      default:     printf ("Unknown error.\n"); break;
    }
  }
  return 0;
}