1 /* fflush.c -- allow flushing input streams
2 Copyright (C) 2007-2009 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 3 of the License, or
7 (at your option) any later version.
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, see <http://www.gnu.org/licenses/>. */
17 /* Written by Eric Blake. */
30 #include "stdio-impl.h"
35 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
37 /* Clear the stream's ungetc buffer, preserving the value of ftello (fp). */
39 clear_ungetc_buffer_preserving_position (FILE *fp)
41 if (fp->_flags & _IO_IN_BACKUP)
42 /* _IO_free_backup_area is a bit complicated. Simply call fseek. */
43 fseek (fp, 0, SEEK_CUR);
48 /* Clear the stream's ungetc buffer. May modify the value of ftello (fp). */
50 clear_ungetc_buffer (FILE *fp)
52 # if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
58 # elif defined __EMX__ /* emx+gcc */
59 if (fp->_ungetc_count > 0)
61 fp->_ungetc_count = 0;
62 fp->_rcount = - fp->_rcount;
64 # elif defined _IOERR /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw */
66 # elif defined __MINT__ /* Atari FreeMiNT */
67 if (fp->__pushed_back)
69 fp->__bufp = fp->__pushback_bufp;
70 fp->__pushed_back = 0;
72 # else /* other implementations */
73 fseek (fp, 0, SEEK_CUR);
79 #if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
82 disable_seek_optimization (FILE *fp)
84 int saved_flags = fp_->_flags & (__SOPT | __SNPT);
85 fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT;
90 restore_seek_optimization (FILE *fp, int saved_flags)
92 fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags;
98 update_fpos_cache (FILE *fp, off_t pos)
100 #if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
102 fp_->_flags |= __SOFF;
106 /* Flush all pending data on STREAM according to POSIX rules. Both
107 output and seekable input streams are supported. */
109 rpl_fflush (FILE *stream)
111 /* When stream is NULL, POSIX and C99 only require flushing of "output
112 streams and update streams in which the most recent operation was not
113 input", and all implementations do this.
115 When stream is "an output stream or an update stream in which the most
116 recent operation was not input", POSIX and C99 requires that fflush
117 writes out any buffered data, and all implementations do this.
119 When stream is, however, an input stream or an update stream in
120 which the most recent operation was input, C99 specifies nothing,
121 and POSIX only specifies behavior if the stream is seekable.
122 mingw, in particular, drops the input buffer, leaving the file
123 descriptor positioned at the end of the input buffer. I.e. ftell
124 (stream) is lost. We don't want to call the implementation's
127 We test ! freading (stream) here, rather than fwriting (stream), because
128 what we need to know is whether the stream holds a "read buffer", and on
129 mingw this is indicated by _IOREAD, regardless of _IOWRT. */
130 if (stream == NULL || ! freading (stream))
131 return fflush (stream);
133 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
135 clear_ungetc_buffer_preserving_position (stream);
137 return fflush (stream);
141 /* Notes about the file-position indicator:
142 1) The file position indicator is incremented by fgetc() and decremented
144 <http://www.opengroup.org/susv3/functions/fgetc.html>
145 "... the fgetc() function shall ... advance the associated file
146 position indicator for the stream ..."
147 <http://www.opengroup.org/susv3/functions/ungetc.html>
148 "The file-position indicator is decremented by each successful
150 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says:
151 "The value of the file-position indicator for the stream after
152 reading or discarding all pushed-back bytes shall be the same
153 as it was before the bytes were pushed back."
154 Here we are discarding all pushed-back bytes. But more specifically,
155 3) <http://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> says:
156 "[After fflush(),] the file offset of the underlying open file
157 description shall be set to the file position of the stream, and
158 any characters pushed back onto the stream by ungetc() ... shall
161 /* POSIX does not specify fflush behavior for non-seekable input
162 streams. Some implementations purge unread data, some return
163 EBADF, some do nothing. */
164 off_t pos = ftello (stream);
171 /* Clear the ungetc buffer. */
172 clear_ungetc_buffer (stream);
174 /* To get here, we must be flushing a seekable input stream, so the
175 semantics of fpurge are now appropriate to clear the buffer. To
176 avoid losing data, the lseek is also necessary. */
178 int result = fpurge (stream);
183 # if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
186 /* Disable seek optimization for the next fseeko call. This tells the
187 following fseeko call to seek to the desired position directly, rather
188 than to seek to a block-aligned boundary. */
189 int saved_flags = disable_seek_optimization (stream);
190 int result = fseeko (stream, pos, SEEK_SET);
192 restore_seek_optimization (stream, saved_flags);
198 pos = lseek (fileno (stream), pos, SEEK_SET);
201 /* After a successful lseek, update the file descriptor's position cache
203 update_fpos_cache (stream, pos);