lib/fwritable.c

   1 /* Retrieve information about a FILE stream.
   2    Copyright (C) 2007-2025 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation, either version 3 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 /* Specification.  */
  20 #include "fwritable.h"
  21
  22 #include "stdio-impl.h"
  23
  24 #if defined EPLAN9                  /* Plan9 */
  25 # include <fcntl.h>
  26 #endif
  27
  28 /* This file is not used on systems that have the __fwritable function,
  29    namely glibc >= 2.2, Solaris >= 7, UnixWare >= 7.1.4.MP4, Cygwin >= 1.7.34,
  30    Android API >= 23, musl libc.  */
  31
  32 bool
  33 fwritable (FILE *fp)
  34 {
  35   /* Most systems provide FILE as a struct and the necessary bitmask in
  36      <stdio.h>, because they need it for implementing getc() and putc() as
  37      fast macros.  */
  38 #if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
  39   /* GNU libc, BeOS, Haiku, Linux libc5 */
  40   return (fp->_flags & _IO_NO_WRITES) == 0;
  41 #elif defined __sferror || defined __DragonFly__ || defined __ANDROID__
  42   /* FreeBSD, NetBSD, OpenBSD, DragonFly, Mac OS X, Cygwin < 1.7.34, Minix 3, Android */
  43   return (fp_->_flags & (__SRW | __SWR)) != 0;
  44 #elif defined __EMX__               /* emx+gcc */
  45   return (fp->_flags & (_IORW | _IOWRT)) != 0;
  46 #elif defined __minix               /* Minix */
  47   return (fp->_flags & _IOWRITE) != 0;
  48 #elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, UnixWare, mingw, MSVC, NonStop Kernel, OpenVMS */
  49   return (fp_->_flag & (_IORW | _IOWRT)) != 0;
  50 #elif defined __QNX__               /* QNX */
  51   return (fp->_Mode & 0x2 /* _MOPENW */) != 0;
  52 #elif defined __MINT__              /* Atari FreeMiNT */
  53   return fp->__mode.__write;
  54 #elif defined EPLAN9                /* Plan9 */
  55   int fd = fp->fd;
  56   if (fd >= 0)
  57     {
  58       int flags = fcntl (fd, F_GETFL, NULL);
  59       if (flags >= 0)
  60         {
  61           flags &= O_ACCMODE;
  62           return (flags == O_WRONLY || flags == O_RDWR);
  63         }
  64     }
  65   return 0;
  66 #else
  67 # error "Please port gnulib fwritable.c to your platform! Look at the definition of fopen, fdopen on your system, then report this to bug-gnulib."
  68 #endif
  69 }