Bug in isatty (BSD4.2)

[hamilton at uiucuxc.Uiuc.ARPA]

regarding the bug in isatty(): this problem has been around as long as
isatty() (since V7 at least).  my solution:

	/*
	 * isatty - determine whether a file is a tty
	 *
	 * isatty (file)
	 *     int file;
	 *
	 * returns 1 if file descriptor 'file' refers to a tty, 0 otherwise.
	 * differs from the standard version in preserving the value
	 * of "errno" across a potentially erroneous "gtty()".
	 *
	 * last modification:  7 aug 82, j w hamilton
	 *
	 */

	#include <sgtty.h>
	extern int errno;

	isatty (file)
		int file;
	{
		register int olderrno = errno;
		struct sgttyb ttyb;

		if (gtty (file, &ttyb) < 0) {
			errno = olderrno;
			return (0);
		}
		return (1);
	}

	wayne ({decvax,ucbvax}!pur-ee!uiucdcs!uiucuxc!)hamilton