Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: stdio on SYSV vrs BSD
Message-ID: <3290@auspex.auspex.com>
Date: 2 May 90 21:25:44 GMT
References: <558@venice.SEDD.TRW.COM> <1990May2.045800.25928@kfw.COM>
Organization: Auspex Systems, Santa Clara
Lines: 20

>>       What is the equivalent on SYSV machines?
>
>I hope to God there isn't one.

Uhh, System V's hack is worse; it sets the file descriptor number for a
"this is really a string" stream to _NFILE, and it *does* do some
special-casing in "_doscan".

The problem with this is that it *hard-codes* the idea that _NFILE is
the number of file descriptors into standard I/O, which sucks because
the maximum number of file descriptors is tunable in later S5 releases. 
Choosing some far out-of-range value such as 255 on unsigned-char
machines and -1 on signed-char machines would have been preferable....

(Yes, I know that S5's standard I/O has a fixed number of "_iob"
entries, and thus couldn't use the extra descriptors anyway.  This is
*not* a valid excuse; 4.3BSD's standard I/O dynamically allocates the
"_iob" stuff, and those techniques could be applied to S5's as well -
definitely so if binary compatibility isn't a concern, and it may be
possible even if it *is* a concern.)