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 clear_ungetc_buffer (FILE *fp)
37 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
38 if (fp->_flags & _IO_IN_BACKUP)
39 /* _IO_free_backup_area is a bit complicated. Simply call fseek. */
40 fseek (fp, 0, SEEK_CUR);
41 #elif defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
50 #if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
53 disable_seek_optimization (FILE *fp)
55 int saved_flags = fp_->_flags & (__SOPT | __SNPT);
56 fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT;
61 restore_seek_optimization (FILE *fp, int saved_flags)
63 fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags;
69 update_fpos_cache (FILE *fp, off_t pos)
71 #if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
73 fp_->_flags |= __SOFF;
77 /* Flush all pending data on STREAM according to POSIX rules. Both
78 output and seekable input streams are supported. */
80 rpl_fflush (FILE *stream)
85 /* When stream is NULL, POSIX and C99 only require flushing of "output
86 streams and update streams in which the most recent operation was not
87 input", and all implementations do this.
89 When stream is "an output stream or an update stream in which the most
90 recent operation was not input", POSIX and C99 requires that fflush
91 writes out any buffered data, and all implementations do this.
93 When stream is, however, an input stream or an update stream in
94 which the most recent operation was input, C99 specifies nothing,
95 and POSIX only specifies behavior if the stream is seekable.
96 mingw, in particular, drops the input buffer, leaving the file
97 descriptor positioned at the end of the input buffer. I.e. ftell
98 (stream) is lost. We don't want to call the implementation's
101 We test ! freading (stream) here, rather than fwriting (stream), because
102 what we need to know is whether the stream holds a "read buffer", and on
103 mingw this is indicated by _IOREAD, regardless of _IOWRT. */
104 if (stream == NULL || ! freading (stream))
105 return fflush (stream);
107 /* Clear the ungetc buffer.
109 This is needed before fetching the file-position indicator, because
110 1) The file position indicator is incremented by fgetc() and decremented
112 <http://www.opengroup.org/susv3/functions/fgetc.html>
113 "... the fgetc() function shall ... advance the associated file
114 position indicator for the stream ..."
115 <http://www.opengroup.org/susv3/functions/ungetc.html>
116 "The file-position indicator is decremented by each successful
118 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says:
119 "The value of the file-position indicator for the stream after
120 reading or discarding all pushed-back bytes shall be the same
121 as it was before the bytes were pushed back."
122 3) Here we are discarding all pushed-back bytes.
124 Unfortunately it is impossible to implement this on platforms with
125 _IOERR, because an ungetc() on this platform prepends the pushed-back
126 bytes to the buffer without an indication of the limit between the
127 pushed-back bytes and the read-ahead bytes. */
128 clear_ungetc_buffer (stream);
130 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
132 return fflush (stream);
136 /* POSIX does not specify fflush behavior for non-seekable input
137 streams. Some implementations purge unread data, some return
138 EBADF, some do nothing. */
139 pos = ftello (stream);
146 /* To get here, we must be flushing a seekable input stream, so the
147 semantics of fpurge are now appropriate to clear the buffer. To
148 avoid losing data, the lseek is also necessary. */
149 result = fpurge (stream);
153 # if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
156 /* Disable seek optimization for the next fseeko call. This tells the
157 following fseeko call to seek to the desired position directly, rather
158 than to seek to a block-aligned boundary. */
159 int saved_flags = disable_seek_optimization (stream);
161 result = fseeko (stream, pos, SEEK_SET);
163 restore_seek_optimization (stream, saved_flags);
169 pos = lseek (fileno (stream), pos, SEEK_SET);
172 /* After a successful lseek, update the file descriptor's position cache
174 update_fpos_cache (stream, pos);