new stdio

[unix-history] / usr / src / lib / libc / stdio / freopen.c

/*-
* Copyright (c) 1990 The Regents of the University of California.
* All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Chris Torek.
*
* %sccs.include.redist.c%
*/

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)freopen.c   5.3 (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include "local.h"

/* 
* Re-direct an existing, open (probably) file to some other file. 
* ANSI is written such that the original file gets closed if at
* all possible, no matter what.
*/
FILE *
freopen(file, mode, fp)
       char *file, *mode;
       register FILE *fp;
{
       register int f;
       int flags, isopen, oflags, sverrno, wantfd;

       if ((flags = __sflags(mode, &oflags)) == 0) {
               (void) fclose(fp);
               return (NULL);
       }

       if (!__sdidinit)
               __sinit();

       /*
        * There are actually programs that depend on being able to "freopen"
        * descriptors that weren't originally open.  Keep this from breaking.
        * Remember whether the stream was open to begin with, and which file
        * descriptor (if any) was associated with it.  If it was attached to
        * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
        * should work.  This is unnecessary if it was not a Unix file.
        */
       if (fp->_flags == 0) {
               fp->_flags = __SEOF;    /* hold on to it */
               isopen = 0;
               wantfd = -1;
       } else {
               /* flush the stream; ANSI doesn't require this. */
               if (fp->_flags & __SWR)
                       (void) fflush(fp);
               /* if close is NULL, closing is a no-op, hence pointless */
               isopen = fp->_close != NULL;
               if ((wantfd = fp->_file) < 0 && isopen) {
                       (void) (*fp->_close)(fp->_cookie);
                       isopen = 0;
               }
       }

       /* Get a new descriptor to refer to the new file. */
       f = open(file, oflags, DEFFILEMODE);
       if (f < 0 && isopen) {
               /* If out of fd's close the old one and try again. */
               if (errno == ENFILE || errno == EMFILE) {
                       (void) (*fp->_close)(fp->_cookie);
                       isopen = 0;
                       f = open(file, oflags, DEFFILEMODE);
               }
       }
       sverrno = errno;

       /*
        * Finish closing fp.  Even if the open succeeded above, we cannot
        * keep fp->_base: it may be the wrong size.  This loses the effect
        * of any setbuffer calls, but stdio has always done this before.
        */
       if (isopen)
               (void) (*fp->_close)(fp->_cookie);
       if (fp->_flags & __SMBF)
               free((char *)fp->_bf._base);
       fp->_w = 0;
       fp->_r = 0;
       fp->_p = NULL;
       fp->_bf._base = NULL;
       fp->_bf._size = 0;
       fp->_lbfsize = 0;
       if (HASUB(fp))
               FREEUB(fp);
       fp->_ub._size = 0;
       if (HASLB(fp))
               FREELB(fp);
       fp->_lb._size = 0;

       if (f < 0) {                    /* did not get it after all */
               fp->_flags = 0;         /* set it free */
               errno = sverrno;        /* restore in case _close clobbered */
               return (NULL);
       }

       /*
        * If reopening something that was open before on a real file, try
        * to maintain the descriptor.  Various C library routines (perror)
        * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
        */
       if (wantfd >= 0 && f != wantfd) {
               if (dup2(f, wantfd) >= 0) {
                       (void) close(f);
                       f = wantfd;
               }
       }

       fp->_flags = flags;
       fp->_file = f;
       fp->_cookie = fp;
       fp->_read = __sread;
       fp->_write = __swrite;
       fp->_seek = __sseek;
       fp->_close = __sclose;
       return (fp);
}