Date: Thu, 10 Jun 1999 10:46:24 +0300 (IDT)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: "Mark E." <snowball3 AT bigfoot DOT com>
cc: djgpp-workers AT delorie DOT com
Subject: Re: enhancements to fcntl.c
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On Mon, 7 Jun 1999, Mark E. wrote:

> From looking over the source and the interrupt list, I don't think even 
> O_APPEND can be set with F_SETFL since it's only used when the file 
> is open and it isn't stored in the SFT.

This actually means we have a bug in the library, as the attached two
test programs will demonstrate: `open' with O_APPEND and `fopen' with
"a" do NOT position the file pointer at EOF prior to every write,
contrary to what ANSI and Posix say.

I'm not sure whether this will be fixed in v2.03 or postponed till
2.04 (after all, this bug probably goes back to v2.0, and AFAIK nobody
complained until now), but in any case it *will* be solved before the
improved `fcntl' hits the street.

A simple way to fix it would be to record the O_APPEND bit in the
__file_handle_modes[] array, where currently we only record the
binary/text bit, and force lseek/fseek on every write.  So I think
`fcntl' can use __file_handle_modes[] for peeking at O_APPEND and
poking it.

-------------------------------------------------------------------
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

int main (void)
{
  static char line_1[] = "This is the first line\n";
  static char line_2[] = "And this is the second line\n";
  int fd = open ("open.dat", O_RDWR | O_APPEND, 0666);

  if (fd > 2)
    {
      write (fd, line_1, sizeof (line_1) - 1);
      lseek (fd, 0L, SEEK_SET);
      write (fd, line_2, sizeof (line_2) - 1);
      if (close (fd))
	perror ("closing file");
    }

  return 0;
}

#include <stdio.h>

int main (void)
{
  static char line_1[] = "This is the first line\n";
  static char line_2[] = "And this is the second line\n";
  FILE *fp = fopen ("fopen.dat", "a+");

  if (fp)
    {
      fwrite (line_1, 1, sizeof (line_1) - 1, fp);
      fseek (fp, 0L, SEEK_SET);
      fwrite (line_2, 1, sizeof (line_2) - 1, fp);
      if (fclose (fp))
	perror ("closing file");
    }

  return 0;
}