lib/fseterr.c

/* Set the error indicator of a stream.
   Copyright (C) 2007-2026 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include "fseterr.h"

#include <errno.h>

#include "stdio-impl.h"

/* This file is not used on systems that have the __fseterr function,
   namely OpenBSD >= 7.6, musl libc, Haiku >= hrev58760.  */

void
fseterr (FILE *fp)
{
  /* Most systems provide FILE as a struct and the necessary bitmask in
     <stdio.h>, because they need it for implementing getc() and putc() as
     fast macros.  */
#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
  /* GNU libc, BeOS, Haiku, Linux libc5 */
  fp->_flags |= _IO_ERR_SEEN;
#elif defined __sferror || defined __DragonFly__ || defined __ANDROID__
  /* FreeBSD, NetBSD, OpenBSD < 7.6, DragonFly, Mac OS X, Cygwin, Minix 3, Android */
  fp_->_flags |= __SERR;
#elif defined __EMX__               /* emx+gcc */
  fp->_flags |= _IOERR;
#elif defined __minix               /* Minix */
  fp->_flags |= _IOERR;
#elif defined _IOERR                /* AIX, HP-UX, Solaris, OpenServer, UnixWare, mingw, MSVC, NonStop Kernel, OpenVMS */
  fp_->_flag |= _IOERR;
#elif defined __UCLIBC__            /* uClibc */
  fp->__modeflags |= __FLAG_ERROR;
#elif defined __QNX__               /* QNX */
  fp->_Mode |= 0x200 /* _MERR */;
#elif defined __MINT__              /* Atari FreeMiNT */
  fp->__error = 1;
#elif defined EPLAN9                /* Plan9 */
  if (fp->state != 0 /* CLOSED */)
    fp->state = 5 /* ERR */;
#elif 0                             /* unknown  */
  /* Portable fallback, based on an idea by Rich Felker.
     Wow! 6 system calls for something that is just a bit operation!
     Not activated on any system, because there is no way to repair FP when
     the sequence of system calls fails, and library code should not call
     abort().  */
  int saved_errno = errno;
  fflush (fp);
  int fd = fileno (fp);
  int fd2 = dup (fd);
  if (fd2 >= 0)
    {
      close (fd);
      fputc ('\0', fp); /* This should set the error indicator.  */
      fflush (fp);      /* Or this.  */
      if (dup2 (fd2, fd) < 0)
        /* Whee... we botched the stream and now cannot restore it!  */
        abort ();
      close (fd2);
    }
  errno = saved_errno;
#else
 #error "Please port gnulib fseterr.c to your platform! Look at the definitions of ferror and clearerr on your system, then report this to bug-gnulib."
#endif
}