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. */
32 /* Flush all pending data on STREAM according to POSIX rules. Both
33 output and seekable input streams are supported. */
35 rpl_fflush (FILE *stream)
40 /* When stream is NULL, POSIX and C99 only require flushing of "output
41 streams and update streams in which the most recent operation was not
42 input", and all implementations do this.
44 When stream is "an output stream or an update stream in which the most
45 recent operation was not input", POSIX and C99 requires that fflush
46 writes out any buffered data, and all implementations do this.
48 When stream is, however, an input stream or an update stream in
49 which the most recent operation was input, C99 specifies nothing,
50 and POSIX only specifies behavior if the stream is seekable.
51 mingw, in particular, drops the input buffer, leaving the file
52 descriptor positioned at the end of the input buffer. I.e. ftell
53 (stream) is lost. We don't want to call the implementation's
56 We test ! freading (stream) here, rather than fwriting (stream), because
57 what we need to know is whether the stream holds a "read buffer", and on
58 mingw this is indicated by _IOREAD, regardless of _IOWRT. */
59 if (stream == NULL || ! freading (stream))
60 return fflush (stream);
62 /* Clear the ungetc buffer.
64 This is needed before fetching the file-position indicator, because
65 1) The file position indicator is incremented by fgetc() and decremented
67 <http://www.opengroup.org/susv3/functions/fgetc.html>
68 "... the fgetc() function shall ... advance the associated file
69 position indicator for the stream ..."
70 <http://www.opengroup.org/susv3/functions/ungetc.html>
71 "The file-position indicator is decremented by each successful
73 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says:
74 "The value of the file-position indicator for the stream after
75 reading or discarding all pushed-back bytes shall be the same
76 as it was before the bytes were pushed back."
77 3) Here we are discarding all pushed-back bytes.
79 Unfortunately it is impossible to implement this on platforms with
80 _IOERR, because an ungetc() on this platform prepends the pushed-back
81 bytes to the buffer without an indication of the limit between the
82 pushed-back bytes and the read-ahead bytes. */
83 #if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
85 # if defined __NetBSD__ || defined __OpenBSD__
88 struct __sbuf _ub; /* ungetc buffer */
89 /* More fields, not relevant here. */
91 if (((struct __sfileext *) stream->_ext._base)->_ub._base != NULL)
93 if (stream->_ub._base != NULL)
96 stream->_p += stream->_r;
102 /* POSIX does not specify fflush behavior for non-seekable input
103 streams. Some implementations purge unread data, some return
104 EBADF, some do nothing. */
105 pos = ftello (stream);
112 /* To get here, we must be flushing a seekable input stream, so the
113 semantics of fpurge are now appropriate to clear the buffer. To
114 avoid losing data, the lseek is also necessary. */
115 result = fpurge (stream);
119 #if defined __sferror && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
122 /* Disable seek optimization for the next fseeko call. This tells the
123 following fseeko call to seek to the desired position directly, rather
124 than to seek to a block-aligned boundary. */
125 int saved_flags = stream->_flags & (__SOPT | __SNPT);
126 stream->_flags = (stream->_flags & ~__SOPT) | __SNPT;
128 result = fseeko (stream, pos, SEEK_SET);
130 stream->_flags = (stream->_flags & ~(__SOPT | __SNPT)) | saved_flags;
136 pos = lseek (fileno (stream), pos, SEEK_SET);
139 /* After a successful lseek, update the file descriptor's position cache
141 # if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
142 stream->_offset = pos;
143 stream->_flags |= __SOFF;