Path: utzoo!attcan!uunet!mailrus!uflorida!travis!brad
From: brad@SSD.CSD.HARRIS.COM (Brad Appleton)
Newsgroups: comp.lang.c
Subject: Re: How do you tell if stdin/stdout is a terminal?
Summary: use isatty() (assuming you are on a UNIX system)
Keywords: stdin/stdout, unix, C, redirected I/O
Message-ID: <613@travis.csd.harris.com>
Date: 6 Aug 90 15:32:20 GMT
References: <12210@hydra.gatech.EDU> <2072@bimacs.BITNET>
Sender: news@travis.csd.harris.com
Organization: Harris Computers Systems Division, Fort Lauderdale,FL
Lines: 36

In article <2072@bimacs.BITNET> kfir@bimacs.biu.ac.il.UUCP (Yuval Kfir) writes:

(stuff deleted)

>I seem to remember a function called isatty(stdin). I am not sure it is
>standard. I hope this helps.                ^^^^^
>

Thats almost correct, the usage should be:

	isatty(STDIN);

where you have the following #defines

	#define STDIN  0
	#define STDOUT 1
	#define STDERR 2

You need to give it the file-descriptor number, not the file pointer!

Some compilers have the above #defines in their standard header files,
some dont! Also, On some Unix implementations (you will have to check yours),
calling isatty() can set errno to a non-zero value if isatty() returns FALSE.
This is due to the fact that some implementations of isatty() use ioctl()
to make a terminal-specific setting, if ioctl() fails, the file-descriptor
is NOT connected to a terminal.

Anyway, if you are on UNIX, isatty() is the way to go. If you are on another
system - look through your C-Compiler manual! Hope this helps!!

Just for the record - Peter Da Silva helped me figure out why errno
was being set!
______________________ "And miles to go before I sleep." ______________________
 Brad Appleton        brad@travis.ssd.csd.harris.com   Harris Computer Systems
                          ...!uunet!hcx1!brad          Fort Lauderdale, FL USA
~~~~~~~~~~~~~~~~~~~~ Disclaimer: I said it, not my company! ~~~~~~~~~~~~~~~~~~~