1 /* fflush.c -- allow flushing input streams
2 Copyright (C) 2007 Free Software Foundation, Inc.
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 2, or (at your option)
9 This program 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 General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program; if not, write to the Free Software Foundation,
16 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
18 /* Written by Eric Blake. */
33 /* Flush all pending data on STREAM according to POSIX rules. Both
34 output and seekable input streams are supported. */
36 rpl_fflush (FILE *stream)
41 /* When stream is NULL, POSIX and C99 only require flushing of "output
42 streams and update streams in which the most recent operation was not
43 input", and all implementations do this.
45 When stream is "an output stream or an update stream in which the most
46 recent operation was not input", POSIX and C99 requires that fflush
47 writes out any buffered data, and all implementations do this.
49 When stream is, however, an input stream or an update stream in
50 which the most recent operation was input, C99 specifies nothing,
51 and POSIX only specifies behavior if the stream is seekable.
52 mingw, in particular, drops the input buffer, leaving the file
53 descriptor positioned at the end of the input buffer. I.e. ftell
54 (stream) is lost. We don't want to call the implementation's
57 We test ! freading (stream) here, rather than fwriting (stream), because
58 what we need to know is whether the stream holds a "read buffer", and on
59 mingw this is indicated by _IOREAD, regardless of _IOWRT. */
60 if (stream == NULL || ! freading (stream))
61 return fflush (stream);
63 /* POSIX does not specify fflush behavior for non-seekable input
64 streams. Some implementations purge unread data, some return
65 EBADF, some do nothing. */
66 pos = ftello (stream);
73 /* To get here, we must be flushing a seekable input stream, so the
74 semantics of fpurge are now appropriate to clear the buffer. To
75 avoid losing data, the lseek is also necessary. */
76 result = fpurge (stream);
80 pos = lseek (fileno (stream), pos, SEEK_SET);
83 /* After a successful lseek, update the file descriptor's position cache
85 #if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
86 stream->_offset = pos;
87 stream->_flags |= __SOFF;