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Manual page for TERMIOS(3V)

termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed - get and set terminal attributes, line control, get and set baud rate, get and set terminal foreground process group ID

SYNOPSIS

#include <termios.h>
#include <unistd.h>

int tcgetattr(fd, termios_p)
int fd;
struct termios *termios_p;

int tcsetattr(fd, optional_actions, termios_p)
int fd;
int optional_actions;
struct termios *termios_p;

int tcsendbreak(fd, duration)
int fd;
int duration;

int tcdrain(fd)
int fd;

int tcflush(fd, queue_selector)
int fd;
int queue_selector;

int tcflow(fd, action)
int fd;
int action;

speed_t cfgetospeed(termios_p)
struct termios *termios_p;

int cfsetospeed(termios_p, speed)
struct termios *termios_p;
speed_t speed;

speed_t cfgetispeed(termios_p)
struct termios *termios_p;

int cfsetispeed(termios_p, speed)
struct termios *termios_p;
speed_t speed;

#include <sys/types.h>
#include <termios.h>

DESCRIPTION

The termios functions describe a general terminal interface that is provided to control asynchronous communications ports. A more detailed overview of the terminal interface can be found in termio.4 That section also describes an ioctl() interface that can be used to access the same functionality. However, the function interface described here is the preferred user interface.

Many of the functions described here have a termios_p argument that is a pointer to a termios structure. This structure contains the following members:

		tcflag_t	c_iflag;		/* input modes */
		tcflag_t	c_oflag;		/* output modes */
		tcflag_t	c_cflag;		/* control modes */
 		tcflag_t	c_lflag;		/* local modes */
		cc_t	c_cc[NCCS];	/* control chars */

These structure members are described in detail in termio.4

tcgetattr() gets the parameters associated with the object referred by fd and stores them in the termios structure referenced by termios_p. This function may be invoked from a background process; however, the terminal attributes may be subsequently changed by a foreground process.

tcsetattr() sets the parameters associated with the terminal (unless support is required from the underlying hardware that is not available) from the termios structure referred to by termios_p as follows:

The symbolic constants for the values of optional_actions are defined in <sys/termios.h>.

If the terminal is using asynchronous serial data transmission, tcsendbreak() transmits a continuous stream of zero-valued bits for a specific duration. If duration is zero, it transmits zero-valued bits for at least 0.25 seconds, and not more that 0.5 seconds. If duration is not zero, it sends zero-valued bits for duration*N seconds, where N is at least 0.25, and not more than 0.5.

If the terminal is not using asynchronous serial data transmission, tcsendbreak() returns without taking any action.

tcdrain() waits until all output written to the object referred to by fd has been transmitted.

tcflush() discards data written to the object referred to by fd but not transmitted, or data received but not read, depending on the value of queue_selector:

The symbolic constants for the values of queue_selector and action are defined in termios.h.

The default on open of a terminal file is that neither its input nor its output is suspended.

tcflow() suspends transmission or reception of data on the object referred to by fd, depending on the value of actions:

The baud rate functions are provided for getting and setting the values of the input and output baud rates in the termios structure. The effects on the terminal device described below do not become effective until tcsetattr() is successfully called.

The input and output baud rates are stored in the termios structure. The values shown in the table are supported. The names in this table are defined in termios.h

          Name   Description        Name    Description
          ----------------------------------------------
          B0         Hang up       B600        600 baud
          B50        50 baud       B1200      1200 baud
          B75        75 baud       B1800      1800 baud
          B110      110 baud       B2400      2400 baud
          B134    134.5 baud       B4800      4800 baud
          B150      150 baud       B9600      9600 baud
          B200      200 baud       B19200    19200 baud
          B300      300 baud       B38400    38400 baud

cfgetospeed() returns the output baud rate stored in the termios structure pointed to by termios_p.

cfsetospeed() sets the output baud rate stored in the termios structure pointed to by termios_p to speed. The zero baud rate, B0, is used to terminate the connection. If B0 is specified, the modem control lines shall no longer be asserted. Normally, this will disconnect the line.

If the input baud rate is set to zero, the input baud rate will be specified by the value of the output baud rate.

cfgetispeed() returns the input baud rate stored in the termios structure.

cfsetispeed() sets the input baud rate stored in the termios structure to speed.

RETURN VALUES

cfgetispeed() returns the input baud rate stored in the termios structure.

cfgetospeed() returns the output baud rate stored in the termios structure.

cfsetispeed() and cfsetospeed() return:

0
on success.
-1
on failure and sets errno to indicate the error.

All other functions return:

0
on success.
-1
on failure and set errno to indicate the error.

ERRORS

EBADF
The fd argument is not a valid file descriptor.
ENOTTY
The file associated with fd is not a terminal.

tcsetattr() may set errno to:

EINVAL
The optional_actions argument is not a proper value.

An attempt was made to change an attribute represented in the termios structure to an unsupported value.

tcsendbreak() may set errno to:

EINVAL
The device does not support tcsendbreak().

tcdrain() may set errno to:

EINTR
A signal interrupted tcdrain().
EINVAL
The device does not support tcdrain().

tcflush() may set errno to:

EINVAL
The device does not support tcflush().

The queue_selector argument is not a proper value.

tcflow() may set errno to:

EINVAL
The device does not support tcflow().

The action argument is not a proper value.

tcsetattr() may set errno to:

EAGAIN
There is insufficient memory available to copy in the arguments.
EBADF
fd is not a valid descriptor.
EFAULT
Some part of the structure pointed to by termios_p is outside the process's allocated address space.
EINVAL
optional_actions is not valid.
EIO
The calling process is a background process.
ENOTTY
fd does not refer to a terminal device.
ENXIO
The terminal referred to by fd is hung up.

cfsetispeed() and cfsetospeed() may set errno to:

EINVAL
speed is greater than B38400 or less than 0.

SEE ALSO

setpgid.2v setsid.2v termio.4


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Created by unroff & hp-tools. © by Hans-Peter Bischof. All Rights Reserved (1997).

Last modified 21/April/97