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From: chet@odin.INS.CWRU.Edu (Chet Ramey)
Newsgroups: comp.unix.wizards
Subject: Re: dup2
Message-ID: <1991Feb12.205149.22245@usenet.ins.cwru.edu>
Date: 12 Feb 91 20:51:49 GMT
References: <27B1CA1C.22559@ics.uci.edu> <15136@smoke.brl.mil> <richard.666334818@fafnir.la.locus.com>
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In article <richard.666334818@fafnir.la.locus.com> richard@locus.com (Richard M. Mathews) writes:

>I would post what I consider to be the right answer, but I have licensing
>problems.  I can recommend taking ideas from both Gwyn and Ramey; perhaps
>one of them would be willing to post the result of such a merge.

How about this (apologies for the Gnu coding style)?  (As an aside, I do not
think that the second fcntl will ever return EINVAL, since it only returns
that error for out-of-range values (< 0 or >= getdtablesize()), and that
case is already handled explicitly.)

dup2 (fd1, fd2)
     int fd1, fd2;
{
  int saved_errno, r;

  if (fcntl (fd1, F_GETFL, 0) == -1)    /* fd1 is an invalid fd */
    return (-1);

  if (fd2 < 0 || fd2 >= getdtablesize ())	/* This could be removed. */
    {
      errno = EBADF;
      return (-1);
    }

  if (fd1 == fd2)
    return (0);

  saved_errno = errno;
  (void) close (fd2);
  r = fcntl (fd1, F_DUPFD, fd2);

  if (r >= 0)
    errno = saved_errno;
  else
    {
      if (errno == EINVAL)
	errno = EBADF;
    }

  return (r);
}

Chet
-- 
Chet Ramey				``There's just no surf in
Network Services Group			  Cleveland, U.S.A. ...''
Case Western Reserve University
chet@ins.CWRU.Edu		My opinions are just those, and mine alone.