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From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Perror complication
Message-ID: <1019@haddock.ISC.COM>
Date: Mon, 31-Aug-87 10:51:17 EDT
Article-I.D.: haddock.1019
Posted: Mon Aug 31 10:51:17 1987
Date-Received: Fri, 4-Sep-87 05:23:45 EDT
References: <8913@brl-adm.ARPA> <8048@mimsy.UUCP> <18005@amdcad.AMD.COM> <301@ncrcan.UUCP> <18082@amdcad.AMD.COM>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 45
Summary: Fix isatty()

In article <18082@amdcad.AMD.COM> rpw3@amdcad.UUCP (Rob Warnock) writes:
[explanation of the "Not a typewriter" syndrome]

I avoid this problem by using my own copy of isatty(); one which does not have
the side effect of setting errno.  Lately I've noticed some official versions
of isatty() have also fixed this.  If yours doesn't, help yourself to the PD
implementation below.  (Actually, the one I keep in my libhack.a is from an
assembler version.)

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint
---- cut here ----
#!/bin/sh
cat <<\! >bool.h
typedef int bool;
#define YES     1
#define NO      0
!
cat <<\! >isatty.c
/* Test whether a file descriptor is a terminal; preserve errno */
#include "bool.h"
#ifdef USG
#include <sys/termio.h>
#define	ioarg	struct termio
#define	ISATTY	TCGETA
#else
#include <sgtty.h>
#define	ioarg	struct sgttyb
#define	ISATTY	TIOCGETP
#endif

extern int ioctl();

bool isatty(f) int f; {
    extern int errno;
    ioarg dummy;
    register int saverrno = errno;
    if (ioctl(f, ISATTY, &dummy) < 0) {
	errno = saverrno;
	return (NO);
    } else {
	return (YES);
    }
}
!
exit 0