1 /* fflush.c -- allow flushing input streams
2 Copyright (C) 2007-2012 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"
31 #include "unused-parameter.h"
36 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
38 /* Clear the stream's ungetc buffer, preserving the value of ftello (fp). */
40 clear_ungetc_buffer_preserving_position (FILE *fp)
42 if (fp->_flags & _IO_IN_BACKUP)
43 /* _IO_free_backup_area is a bit complicated. Simply call fseek. */
44 fseeko (fp, 0, SEEK_CUR);
49 /* Clear the stream's ungetc buffer. May modify the value of ftello (fp). */
51 clear_ungetc_buffer (FILE *fp)
53 # if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
59 # elif defined __EMX__ /* emx+gcc */
60 if (fp->_ungetc_count > 0)
62 fp->_ungetc_count = 0;
63 fp->_rcount = - fp->_rcount;
65 # elif defined _IOERR /* Minix, AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, NonStop Kernel */
67 # else /* other implementations */
68 fseeko (fp, 0, SEEK_CUR);
74 #if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
77 disable_seek_optimization (FILE *fp)
79 int saved_flags = fp_->_flags & (__SOPT | __SNPT);
80 fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT;
85 restore_seek_optimization (FILE *fp, int saved_flags)
87 fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags;
93 update_fpos_cache (FILE *fp _GL_UNUSED_PARAMETER,
94 off_t pos _GL_UNUSED_PARAMETER)
96 #if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
97 # if defined __CYGWIN__
98 /* fp_->_offset is typed as an integer. */
101 /* fp_->_offset is an fpos_t. */
102 /* Use a union, since on NetBSD, the compilation flags determine
103 whether fpos_t is typedef'd to off_t or a struct containing a
104 single off_t member. */
113 fp_->_flags |= __SOFF;
117 /* Flush all pending data on STREAM according to POSIX rules. Both
118 output and seekable input streams are supported. */
120 rpl_fflush (FILE *stream)
122 /* When stream is NULL, POSIX and C99 only require flushing of "output
123 streams and update streams in which the most recent operation was not
124 input", and all implementations do this.
126 When stream is "an output stream or an update stream in which the most
127 recent operation was not input", POSIX and C99 requires that fflush
128 writes out any buffered data, and all implementations do this.
130 When stream is, however, an input stream or an update stream in
131 which the most recent operation was input, C99 specifies nothing,
132 and POSIX only specifies behavior if the stream is seekable.
133 mingw, in particular, drops the input buffer, leaving the file
134 descriptor positioned at the end of the input buffer. I.e. ftell
135 (stream) is lost. We don't want to call the implementation's
138 We test ! freading (stream) here, rather than fwriting (stream), because
139 what we need to know is whether the stream holds a "read buffer", and on
140 mingw this is indicated by _IOREAD, regardless of _IOWRT. */
141 if (stream == NULL || ! freading (stream))
142 return fflush (stream);
144 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
146 clear_ungetc_buffer_preserving_position (stream);
148 return fflush (stream);
152 /* Notes about the file-position indicator:
153 1) The file position indicator is incremented by fgetc() and decremented
155 <http://www.opengroup.org/susv3/functions/fgetc.html>
156 "... the fgetc() function shall ... advance the associated file
157 position indicator for the stream ..."
158 <http://www.opengroup.org/susv3/functions/ungetc.html>
159 "The file-position indicator is decremented by each successful
161 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says:
162 "The value of the file-position indicator for the stream after
163 reading or discarding all pushed-back bytes shall be the same
164 as it was before the bytes were pushed back."
165 Here we are discarding all pushed-back bytes. But more specifically,
166 3) <http://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> says:
167 "[After fflush(),] the file offset of the underlying open file
168 description shall be set to the file position of the stream, and
169 any characters pushed back onto the stream by ungetc() ... shall
172 /* POSIX does not specify fflush behavior for non-seekable input
173 streams. Some implementations purge unread data, some return
174 EBADF, some do nothing. */
175 off_t pos = ftello (stream);
182 /* Clear the ungetc buffer. */
183 clear_ungetc_buffer (stream);
185 /* To get here, we must be flushing a seekable input stream, so the
186 semantics of fpurge are now appropriate to clear the buffer. To
187 avoid losing data, the lseek is also necessary. */
189 int result = fpurge (stream);
194 # if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
197 /* Disable seek optimization for the next fseeko call. This tells the
198 following fseeko call to seek to the desired position directly, rather
199 than to seek to a block-aligned boundary. */
200 int saved_flags = disable_seek_optimization (stream);
201 int result = fseeko (stream, pos, SEEK_SET);
203 restore_seek_optimization (stream, saved_flags);
209 pos = lseek (fileno (stream), pos, SEEK_SET);
212 /* After a successful lseek, update the file descriptor's position cache
214 update_fpos_cache (stream, pos);