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36 * @(#)freopen.c 8.1 (Berkeley) 6/4/93
37 * $FreeBSD: src/lib/libc/stdio/freopen.c,v 1.5.2.1 2001/03/05 10:54:53 obrien Exp $
38 * $DragonFly: src/lib/libc/stdio/freopen.c,v 1.4 2004/06/08 00:45:00 hmp Exp $
41 #include <sys/types.h>
48 #include "libc_private.h"
52 * Re-direct an existing, open (probably) file to some other file.
53 * ANSI is written such that the original file gets closed if at
54 * all possible, no matter what.
57 freopen(const char *file, const char *mode, FILE *fp)
60 int dflags, flags, isopen, oflags, sverrno, wantfd;
62 if ((flags = __sflags(mode, &oflags)) == 0) {
75 * If the filename is a NULL pointer, the caller is asking us to
76 * re-open the same file with a different mode. We allow this only
77 * if the modes are compatible.
80 /* See comment below regarding freopen() of closed files. */
81 if (fp->_flags == 0) {
86 if ((dflags = fcntl(fp->_file, F_GETFL)) < 0) {
93 if ((dflags & O_ACCMODE) != O_RDWR && (dflags & O_ACCMODE) !=
94 (oflags & O_ACCMODE)) {
100 if ((oflags ^ dflags) & O_APPEND) {
102 dflags |= oflags & O_APPEND;
103 if (fcntl(fp->_file, F_SETFL, dflags) < 0) {
111 if (oflags & O_TRUNC)
112 ftruncate(fp->_file, 0);
113 if (fseeko(fp, 0, oflags & O_APPEND ? SEEK_END : SEEK_SET) < 0 &&
128 * There are actually programs that depend on being able to "freopen"
129 * descriptors that weren't originally open. Keep this from breaking.
130 * Remember whether the stream was open to begin with, and which file
131 * descriptor (if any) was associated with it. If it was attached to
132 * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
133 * should work. This is unnecessary if it was not a Unix file.
135 if (fp->_flags == 0) {
136 fp->_flags = __SEOF; /* hold on to it */
140 /* flush the stream; ANSI doesn't require this. */
141 if (fp->_flags & __SWR)
143 /* if close is NULL, closing is a no-op, hence pointless */
144 isopen = fp->_close != NULL;
145 if ((wantfd = fp->_file) < 0 && isopen) {
146 (void) (*fp->_close)(fp->_cookie);
151 /* Get a new descriptor to refer to the new file. */
152 f = _open(file, oflags, DEFFILEMODE);
153 if (f < 0 && isopen) {
154 /* If out of fd's close the old one and try again. */
155 if (errno == ENFILE || errno == EMFILE) {
156 (void) (*fp->_close)(fp->_cookie);
158 f = _open(file, oflags, DEFFILEMODE);
165 * Finish closing fp. Even if the open succeeded above, we cannot
166 * keep fp->_base: it may be the wrong size. This loses the effect
167 * of any setbuffer calls, but stdio has always done this before.
170 (void) (*fp->_close)(fp->_cookie);
171 if (fp->_flags & __SMBF)
172 free((char *)fp->_bf._base);
176 fp->_bf._base = NULL;
186 if (f < 0) { /* did not get it after all */
187 fp->_flags = 0; /* set it free */
188 errno = sverrno; /* restore in case _close clobbered */
194 * If reopening something that was open before on a real file, try
195 * to maintain the descriptor. Various C library routines (perror)
196 * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
198 if (wantfd >= 0 && f != wantfd) {
199 if (dup2(f, wantfd) >= 0) {
209 fp->_write = __swrite;
211 fp->_close = __sclose;