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Path: utzoo!linus!philabs!cmcl2!floyd!harpo!seismo!hao!hplabs!hp-pcd!hpfcla!hp-dcde!jack
From: jack@hp-dcde.UUCP
Newsgroups: net.jokes.d
Subject: Not a typewriter - (nf)
Message-ID: <2509@hp-pcd.UUCP>
Date: Tue, 22-Nov-83 03:57:49 EST
Article-I.D.: hp-pcd.2509
Posted: Tue Nov 22 03:57:49 1983
Date-Received: Fri, 25-Nov-83 09:27:07 EST
Sender: notes_gateway@hp-pcd.UUCP
Organization: Hewlett-Packard, Fort Collins, CO
Lines: 31

#N:hp-dcde:19600002:000:813
hp-dcde!jack    Nov 17 12:21:00 1983

In response to the "Not a typewriter" error message:

Apparently, the printf stuff calls isatty(3) to find out if a stream
is going to a tty.  If so, it buffers the stream.
However, isatty sets errno (yoiks!) if the stream isn't a tty.
Consider the following sequence:

main()
{
	<try thing that might set errno>;

	if (errno!=0) {
		printf("*** Horrible thing has occured!\n");
		perror("fatal error");
	}
}

The first printf will set errno IF stdout isn't an interactive device,
and hence the perror will print the "Not a typewriter" message.

However, IF stdout is an interactive device, it will work just fine.

Now, I realize that I can save errno right after the error occured,
but I shouldn't have to!  WHY does isatty (and hence printf) set errno???

					-Confused Jack Applin
					 (hplabs!hp-dcd!jack)