1/* fflush.c -- allow flushing input streams 2 Copyright (C) 2007 Free Software Foundation, Inc. 3 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. 8 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. 13 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/>. */ 16 17/* Written by Eric Blake. */ 18 19#include <config.h> 20 21/* Specification. */ 22#include <stdio.h> 23 24#include <errno.h> 25#include <unistd.h> 26 27#include "freading.h" 28#include "fpurge.h" 29 30#undef fflush 31 32/* Flush all pending data on STREAM according to POSIX rules. Both 33 output and seekable input streams are supported. */ 34int 35rpl_fflush (FILE *stream) 36{ 37 int result; 38 off_t pos; 39 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. 43 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. 47 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 54 fflush in this case. 55 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); 61 62 /* POSIX does not specify fflush behavior for non-seekable input 63 streams. Some implementations purge unread data, some return 64 EBADF, some do nothing. */ 65 pos = ftello (stream); 66 if (pos == -1) 67 { 68 errno = EBADF; 69 return EOF; 70 } 71 72 /* To get here, we must be flushing a seekable input stream, so the 73 semantics of fpurge are now appropriate to clear the buffer. To 74 avoid losing data, the lseek is also necessary. */ 75 result = fpurge (stream); 76 if (result != 0) 77 return result; 78 79#if defined __sferror && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */ 80 81 { 82 /* Disable seek optimization for the next fseeko call. This tells the 83 following fseeko call to seek to the desired position directly, rather 84 than to seek to a block-aligned boundary. */ 85 int saved_flags = stream->_flags & (__SOPT | __SNPT); 86 stream->_flags = (stream->_flags & ~__SOPT) | __SNPT; 87 88 result = fseeko (stream, pos, SEEK_SET); 89 90 stream->_flags = (stream->_flags & ~(__SOPT | __SNPT)) | saved_flags; 91 } 92 return result; 93 94#else 95 96 pos = lseek (fileno (stream), pos, SEEK_SET); 97 if (pos == -1) 98 return EOF; 99 /* After a successful lseek, update the file descriptor's position cache 100 in the stream. */ 101# if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */ 102 stream->_offset = pos; 103 stream->_flags |= __SOFF; 104# endif 105 106 return 0; 107 108#endif 109} 110