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From: Josh MacDonald <jmacd@CS.Berkeley.EDU>
Message-Id: <199605022220.PAA17967@paris.CS.Berkeley.EDU>
To: joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch)
Cc: freebsd-hackers@freebsd.org
Subject: Re: stdio problem 
In-reply-to: Your message of "Thu, 02 May 1996 23:04:38 +0200."
             <199605022104.XAA15002@uriah.heep.sax.de> 
Date: Thu, 02 May 1996 15:20:21 -0700
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> As Poul-Henning Kamp wrote:
> 
> > >   close(0);
> > >   if(!freopen(argv[1], "r", stdin)) {
> > 
> > doing a "close(0)" is bound to confuse the stdio library.
> > don't do that.
> 
> More generally spoken, mixing any kind of stdio function (fopen(),
> fclose(), fread(), fwrite(), printf() etc.) with low-level functions
> (syscalls in Unix: open(), close(), read(), write()) is error-prone.
> 
> -- 
> cheers, J"org
> 
> joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE
> Never trust an operating system you don't have sources for. ;-)

Unfortunatly, I don't have control over this condition.  I am closing
the standard input and exec-ing GNU diff3.  Diff3 calls freopen. 
The comments in stdio/freopen.c say this should work.  It works everywhere
else.

Your answers are not very helpful.

Why couldn't you all just answer my questions instead of telling me
it is wrong.  Obviously, I already know that
it doesn't work on FreeBSD or NetBSD, and that it works on every other
operating system I've tried it on.

a)  Why does freopen fail *even though the comments in freopen.c say
    it should not*?

b)  Should GNU diff3 be responsible for checking that stdin is open
    before tring to freopen?

c)  Should I not exec a program without an opened stdin?  Programs
    which assume they have an open stdin are bad, I think.  

-josh