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Path: utzoo!linus!decvax!harpo!floyd!cmcl2!philabs!seismo!rochester!jay
From: jay@rochester.UUCP (Jay Weber)
Newsgroups: net.micro.pc
Subject: Re: DOS 2.0 Problems
Message-ID: <3305@rochester.UUCP>
Date: Fri, 7-Oct-83 20:24:23 EDT
Article-I.D.: rocheste.3305
Posted: Fri Oct  7 20:24:23 1983
Date-Received: Sun, 9-Oct-83 19:03:52 EDT
References: <118@shell.UUCP>
Organization: U. of Rochester, CS Dept.
Lines: 33

In reference to the complaint about CiC86 programs hanging when
you redirect the input:  That is due to the C library interacting
with DOS 2.0.  The function call used in ascii mode is "buffered
keyboard input with echo".  The echo part is why you see the file
printing on the screen whether you printed it or not.  The system
call gets the redirected character from the file, thinking it is 
from the keyboard, and through ignorance, echoes it.  Aha!  You say,
why not use the "no echo" call(s)?  Well, then it won't work
correctly when typing from the keyboard.  You could do an ioctl
function call to find if the input is the console and act accordingly,
but it is probably better and possibly easier to just rewrite
the library routines to do the new 2.0 calls.  I have done some of
this.  When I come up with a universally usable set of new routines,
I'll post them.

The reason why it hangs is because the keyboard input system call
reads until a newline character is fetched; when you redirect the
input, the last character sent is a ^Z -- what you see on the
screen is the ^Z echoed, and it is waiting for a newline that
you cannot give.  Frustrating, since it is inside a system call
"never to return", so you cannot BREAK it.  Rebooting is the only
thing to do.  A quick fix might be to change the library routines to
not use the buffered system calls.

By the way, I wrote a very tiny but handy c routine, called safe().
All it does is check to see if there is a character on the input,
discard the result, and return.  What it does is allow you to
BREAK out of infinite loops if a call to safe() is inside the
loop.  Helps out alot in debugging, becasue I hate rebooting
when. I screw something up.

-Jay Weber
{jay@rochester, ..!seismo!rochester!jay}