How can I implement the isatty() in C language

**Garrick** · 11-02-2010

Hi, I am the student of the Programming Field. I had learned the C language. I can also have the knowledge of the functions. But I could not know about the isatty() function of C language. So that I would like to know about use of the isatty() function of C language. I also would like to know how can isatty() function can be implemented in the C program. If you have the answer for me then reply me.

**Modifier** · 11-02-2010

To determine that if the file descriptor fields can be associated with a terminal, the isatty() function can be used in the C language. The following can be the general syntax of the isatty() function :

Code:

#include <unistd.h>
int isatty( int fs );

**Praetor** · 11-02-2010

The following code of lines can demonstrates you about the working of the isatty() function in the C language :

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
void main()
  {
    exit( isatty( 3 ) ? EXIT_SUCCESS : EXIT_FAILURE );
  }

**Katty** · 11-02-2010

PROGRAM :

Code:

#if defined(LIBC_SCCS) && !defined(lint)
static char *rcid = "$Id: isatty.c,v 1.1.1.1 2000/02/10 01:00:58 sasha Exp $";
#endif 
#include <pthread.h>
#ifdef snos4
#include <sys/termio.h>
#else
#include <termios.h>
#endif
#include <unistd.h>
#ifndef TICGETA
#ifdef TGETATTR
#define TICGETA    TGETATTR
#else
#ifndef TGETA
#include <termio.h>
#endif 
#ifndef TICGETA
#define TICGETA    TGETA
#endif
#endif 
#endif
int isatty_basic(int f)
{
#ifdef snos4
	struct termi v;
#else 
	struct termo v;
#endif 
	return (machdep_sys_ioctl(f,
#ifdef snos4
				  TGETA,
#else 
				  TICGETA,
#endif 
				  &v) ? 0 : 1);
}
int isatty(int f)
{
	int rt;
	if ((rt = f_lock(f, FD_READ, NULL)) == OK) 
{
		rt = isatty_basic(f_table[f]->f.i);
		f_unlock(f, FD_READ);
	} else 
{
		rt = 0;
	}
	return(rt);
}

**kelfro** · 11-02-2010

The following program can states you the working of the isatty() function :

Code:

#define _POSIX_SOURCE
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
void checkfd(int d)
 {
  printf("fd %d is ", d);
  if (!isatty(d))
    printf("NOT ");
  puts("a tty");
}
main() 
{
  int q[2], d;
  char n[]="temp.file";
  if (pipe(q) != 0)
    perror("pipe() error");
  else 
{
    if ((d = creat(n, SIWUSR)) < 0)
      perror("creat() error");
    else 
{
      checkfd(0);
      checkfd(fileno(stderr));
      checkfd(q[1]);
      checkfd(d);
      close(d);
      unlink(n);
    }
    close(q[0]);
    close(q[1]);
  }
}

Output :

Code:

fd 0 is a tty
fd 2 is a tty
fd 4 is NOT a tty
fd 5 is NOT a tty

**Zecho** · 11-02-2010

The isatty() function can only be works in an environment where either a controlling terminal exists. The isatty() function can not work in a TSO environment. The isatty() function can returns zero if the given file descriptor can not be a terminal. The isatty() function can returns one if the given file descriptor can be a terminal.