1 /* fflush.c -- allow flushing input streams
2 Copyright (C) 2007-2008 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. */
33 clear_ungetc_buffer (FILE *fp)
35 #if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
36 # if defined __NetBSD__ || defined __OpenBSD__
39 struct __sbuf _ub; /* ungetc buffer */
40 /* More fields, not relevant here. */
42 # define HASUB(fp) (((struct __sfileext *) (fp)->_ext._base)->_ub._base != NULL)
44 # define HASUB(fp) ((fp)->_ub._base != NULL)
54 #if defined __sferror && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
57 disable_seek_optimization (FILE *fp)
59 int saved_flags = fp->_flags & (__SOPT | __SNPT);
60 fp->_flags = (fp->_flags & ~__SOPT) | __SNPT;
65 restore_seek_optimization (FILE *fp, int saved_flags)
67 fp->_flags = (fp->_flags & ~(__SOPT | __SNPT)) | saved_flags;
73 update_fpos_cache (FILE *fp)
75 #if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
81 /* Flush all pending data on STREAM according to POSIX rules. Both
82 output and seekable input streams are supported. */
84 rpl_fflush (FILE *stream)
89 /* When stream is NULL, POSIX and C99 only require flushing of "output
90 streams and update streams in which the most recent operation was not
91 input", and all implementations do this.
93 When stream is "an output stream or an update stream in which the most
94 recent operation was not input", POSIX and C99 requires that fflush
95 writes out any buffered data, and all implementations do this.
97 When stream is, however, an input stream or an update stream in
98 which the most recent operation was input, C99 specifies nothing,
99 and POSIX only specifies behavior if the stream is seekable.
100 mingw, in particular, drops the input buffer, leaving the file
101 descriptor positioned at the end of the input buffer. I.e. ftell
102 (stream) is lost. We don't want to call the implementation's
105 We test ! freading (stream) here, rather than fwriting (stream), because
106 what we need to know is whether the stream holds a "read buffer", and on
107 mingw this is indicated by _IOREAD, regardless of _IOWRT. */
108 if (stream == NULL || ! freading (stream))
109 return fflush (stream);
111 /* Clear the ungetc buffer.
113 This is needed before fetching the file-position indicator, because
114 1) The file position indicator is incremented by fgetc() and decremented
116 <http://www.opengroup.org/susv3/functions/fgetc.html>
117 "... the fgetc() function shall ... advance the associated file
118 position indicator for the stream ..."
119 <http://www.opengroup.org/susv3/functions/ungetc.html>
120 "The file-position indicator is decremented by each successful
122 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says:
123 "The value of the file-position indicator for the stream after
124 reading or discarding all pushed-back bytes shall be the same
125 as it was before the bytes were pushed back."
126 3) Here we are discarding all pushed-back bytes.
128 Unfortunately it is impossible to implement this on platforms with
129 _IOERR, because an ungetc() on this platform prepends the pushed-back
130 bytes to the buffer without an indication of the limit between the
131 pushed-back bytes and the read-ahead bytes. */
132 clear_ungetc_buffer (stream);
134 /* POSIX does not specify fflush behavior for non-seekable input
135 streams. Some implementations purge unread data, some return
136 EBADF, some do nothing. */
137 pos = ftello (stream);
144 /* To get here, we must be flushing a seekable input stream, so the
145 semantics of fpurge are now appropriate to clear the buffer. To
146 avoid losing data, the lseek is also necessary. */
147 result = fpurge (stream);
151 #if defined __sferror && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
154 /* Disable seek optimization for the next fseeko call. This tells the
155 following fseeko call to seek to the desired position directly, rather
156 than to seek to a block-aligned boundary. */
157 int saved_flags = disable_seek_optimization (stream);
159 result = fseeko (stream, pos, SEEK_SET);
161 restore_seek_optimization (stream, saved_flags);
167 pos = lseek (fileno (stream), pos, SEEK_SET);
170 /* After a successful lseek, update the file descriptor's position cache
172 update_fpos_cache (stream);