Advanced Programming in the UNIX® Environment

ptg10805159

Section 18.9 Te rminal Identification 695

Note that we can’t protect against overrunning the caller’s buffer,because we have

no way to determine its size.

Twofunctions that aremoreinteresting for a UNIX system areisatty,which

returns true if a file descriptor refers to a terminal device, andttyname,which returns

the pathname of the terminal device that is open on a file descriptor.

#include <unistd.h>

int isatty(intfd);

Returns: 1 (true) if terminal device, 0 (false) otherwise

char *ttyname(intfd);

Returns: pointer to pathname of terminal,NULLon error

Example —isattyFunction

Theisattyfunction is trivial to implement, as we show in Figure18.13. Wesimply try

one of the terminal-specific functions (that doesn’t change anything if it succeeds) and

look at the return value.

#include <termios.h>

int

isatty(int fd)

{

struct termios ts;

return(tcgetattr(fd, &ts) != -1); /* true if no error (is a tty) */

}

Figure 18.13Implementation of POSIX.1isattyfunction

We test ourisattyfunction with the program in Figure18.14.

#include "apue.h"

int

main(void)

{

printf("fd 0: %s\n", isatty(0)? "tty" : "not a tty");

printf("fd 1: %s\n", isatty(1)? "tty" : "not a tty");

printf("fd 2: %s\n", isatty(2)? "tty" : "not a tty");

exit(0);

}

Figure 18.14Te st theisattyfunction