Path: utzoo!utgpu!watserv1!ria!uwovax!7103_2622
From: 7103_2622@uwovax.uwo.ca (Eric Smith)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: MicroRTX patch and isatty() fix
Message-ID: <6680.26c75e67@uwovax.uwo.ca>
Date: 14 Aug 90 06:13:59 GMT
References: <4352@bdt.UUCP>
Lines: 36

In article <4352@bdt.UUCP>, david@bdt.UUCP (David Beckemeyer) writes:
> Recently it was brought to my attention that the isatty() code in
> the dLibs and GCC libraries doesn't work with programs run under
> Micro RTX because RTX handles the Fseek() GEMDOS call a little
> differently.
> 
> Basically the isatty() code tries to do Fseek() and if it gets a
> zero back, it assumes the thing isn't seekable and therefore must
> be a tty.  In RTX, Fseek() returns -37 (invalid handle) on non
> seekable files.  This confuses the isatty() code.   Below is a
> program (uuencoded) that will patch RTX V1.13 so that RTX Fseek()
> returns zero like normal GEMDOS Fseek().
> 
> This doesn't fix the whole problem, because the isatty() still
> doesn't understand what to do with pipes.  Basically all the isatty()
> routines that I've seen assume that if the handle is seekable, then
> it's a file, otherwise it's a tty.  Well in RTX, a handle could be
> a pipe, in which case it's not seekable, but it's not a tty either
> (it should be treated like a file).

The GCC isatty() code has a default return value of 0, i.e. if an
error occurs, it's assumed that the handle is not a tty. Thus, if
pipes give an error (e.g. -37, as they used to in RTX) and real ttys always
return 0 from an Fseek, then it can distinguish between them. This
might be a more robust scheme than doing the same thing for ttys and
pipes (it's the solution I chose for my multitasking system).

I presume the dLibs code does something similar, since there was a message
from someone (A. Pratt, perhaps?) describing this as the "official"
way to do isatty().
--
Eric R. Smith                     email:
Dept. of Mathematics            ersmith@uwovax.uwo.ca
University of Western Ontario   ersmith@uwovax.bitnet
London, Ont. Canada N6A 5B7
ph: (519) 661-3638