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From: richard@locus.com (Richard M. Mathews)
Newsgroups: comp.unix.wizards
Subject: Re: dup2() system call
Message-ID: <richard.672371046@werth.la.locus.com>
Date: 23 Apr 91 01:44:06 GMT
References: <85@morwyn.UUCP> <1991Apr20.174307.20637@NCoast.ORG>
Organization: Locus Computing Corporation, Los Angeles, California
Lines: 26

allbery@NCoast.ORG (Brandon S. Allbery KB8JRR/AA) writes:

>(Doug Gwyn's dup2() omitted)

>Reference's sake, yes --- but that was one that got some remarks about
>differing errno values.  (Which is why I had that remark in my comments.)

Actually, the problem with Gwyn's version is the behavior when, on entry
to the routine,
	newfd is a valid descriptor for an open file
	oldfd is not a valid descriptor for an open file
A real dup2 (as on V7) will return EBADF and leave newfd alone.
Gwyn's will return EBADF and close newfd.

>For almost every use of dup2() I've ever encountered, the macro does the job.
>If you absolutely NEED 100% V7 compatibility, use Doug's by all means.

I had problems with the super-simple-minded version of dup2 when porting
the BSD4.1 C Shell.  I don't remember if it was the above problem or the
problem with newfd==oldfd (I think it was the latter, and Gwyn's addresses
that).

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