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. */
29 #include "stdio-impl.h"
34 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
36 /* Clear the stream's ungetc buffer, preserving the value of ftello (fp). */
38 clear_ungetc_buffer_preserving_position (FILE *fp)
40 if (fp->_flags & _IO_IN_BACKUP)
41 /* _IO_free_backup_area is a bit complicated. Simply call fseek. */
42 fseek (fp, 0, SEEK_CUR);
47 /* Clear the stream's ungetc buffer. May modify the value of ftello (fp). */
49 clear_ungetc_buffer (FILE *fp)
51 # if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
57 # elif defined __EMX__ /* emx+gcc */
58 if (fp->_ungetc_count > 0)
60 fp->_ungetc_count = 0;
61 fp->_rcount = - fp->_rcount;
63 # elif defined _IOERR /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw */
65 # else /* other implementations */
66 fseek (fp, 0, SEEK_CUR);
72 #if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
75 disable_seek_optimization (FILE *fp)
77 int saved_flags = fp_->_flags & (__SOPT | __SNPT);
78 fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT;
83 restore_seek_optimization (FILE *fp, int saved_flags)
85 fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags;
91 update_fpos_cache (FILE *fp, off_t pos)
93 #if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
95 fp_->_flags |= __SOFF;
99 /* Flush all pending data on STREAM according to POSIX rules. Both
100 output and seekable input streams are supported. */
102 rpl_fflush (FILE *stream)
104 /* When stream is NULL, POSIX and C99 only require flushing of "output
105 streams and update streams in which the most recent operation was not
106 input", and all implementations do this.
108 When stream is "an output stream or an update stream in which the most
109 recent operation was not input", POSIX and C99 requires that fflush
110 writes out any buffered data, and all implementations do this.
112 When stream is, however, an input stream or an update stream in
113 which the most recent operation was input, C99 specifies nothing,
114 and POSIX only specifies behavior if the stream is seekable.
115 mingw, in particular, drops the input buffer, leaving the file
116 descriptor positioned at the end of the input buffer. I.e. ftell
117 (stream) is lost. We don't want to call the implementation's
120 We test ! freading (stream) here, rather than fwriting (stream), because
121 what we need to know is whether the stream holds a "read buffer", and on
122 mingw this is indicated by _IOREAD, regardless of _IOWRT. */
123 if (stream == NULL || ! freading (stream))
124 return fflush (stream);
126 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
128 clear_ungetc_buffer_preserving_position (stream);
130 return fflush (stream);
134 /* Notes about the file-position indicator:
135 1) The file position indicator is incremented by fgetc() and decremented
137 <http://www.opengroup.org/susv3/functions/fgetc.html>
138 "... the fgetc() function shall ... advance the associated file
139 position indicator for the stream ..."
140 <http://www.opengroup.org/susv3/functions/ungetc.html>
141 "The file-position indicator is decremented by each successful
143 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says:
144 "The value of the file-position indicator for the stream after
145 reading or discarding all pushed-back bytes shall be the same
146 as it was before the bytes were pushed back."
147 Here we are discarding all pushed-back bytes. But more specifically,
148 3) <http://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> says:
149 "[After fflush(),] the file offset of the underlying open file
150 description shall be set to the file position of the stream, and
151 any characters pushed back onto the stream by ungetc() ... shall
154 /* POSIX does not specify fflush behavior for non-seekable input
155 streams. Some implementations purge unread data, some return
156 EBADF, some do nothing. */
157 off_t pos = ftello (stream);
164 /* Clear the ungetc buffer. */
165 clear_ungetc_buffer (stream);
167 /* To get here, we must be flushing a seekable input stream, so the
168 semantics of fpurge are now appropriate to clear the buffer. To
169 avoid losing data, the lseek is also necessary. */
171 int result = fpurge (stream);
176 # if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
179 /* Disable seek optimization for the next fseeko call. This tells the
180 following fseeko call to seek to the desired position directly, rather
181 than to seek to a block-aligned boundary. */
182 int saved_flags = disable_seek_optimization (stream);
183 int result = fseeko (stream, pos, SEEK_SET);
185 restore_seek_optimization (stream, saved_flags);
191 pos = lseek (fileno (stream), pos, SEEK_SET);
194 /* After a successful lseek, update the file descriptor's position cache
196 update_fpos_cache (stream, pos);