TCSETATTR(3) BSD Library Functions Manual TCSETATTR(3)NAME
cfgetispeed, cfsetispeed, cfgetospeed, cfsetospeed, cfsetspeed,
cfmakeraw, tcgetattr, tcsetattr — manipulating the termios structure
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <termios.h>
speed_t
cfgetispeed(const struct termios *t);
int
cfsetispeed(struct termios *t, speed_t speed);
speed_t
cfgetospeed(const struct termios *t);
int
cfsetospeed(struct termios *t, speed_t speed);
int
cfsetspeed(struct termios *t, speed_t speed);
void
cfmakeraw(struct termios *t);
int
tcgetattr(int fd, struct termios *t);
int
tcsetattr(int fd, int action, const struct termios *t);
DESCRIPTION
The cfmakeraw(), tcgetattr() and tcsetattr() functions are provided for
getting and setting the termios structure.
The cfgetispeed(), cfsetispeed(), cfgetospeed(), cfsetospeed() and
cfsetspeed() functions are provided for getting and setting the baud rate
values in the termios structure. The effects of the functions on the
terminal as described below do not become effective, nor are all errors
detected, until the tcsetattr() function is called. Certain values for
baud rates set in the termios structure and passed to tcsetattr() have
special meanings. These are discussed in the portion of the manual page
that describes the tcsetattr() function.
GETTING AND SETTING THE BAUD RATE
The input and output baud rates are found in the termios structure. The
unsigned integer speed_t is typedef'd in the include file <termios.h>.
The value of the integer corresponds directly to the baud rate being rep‐
resented, however, the following symbolic values are defined.
#define B0 0
#define B50 50
#define B75 75
#define B110 110
#define B134 134
#define B150 150
#define B200 200
#define B300 300
#define B600 600
#define B1200 1200
#define B1800 1800
#define B2400 2400
#define B4800 4800
#define B9600 9600
#define B19200 19200
#define B38400 38400
#ifndef _POSIX_SOURCE
#define EXTA 19200
#define EXTB 38400
#endif /*_POSIX_SOURCE */
The cfgetispeed() function returns the input baud rate in the termios
structure referenced by tp.
The cfsetispeed() function sets the input baud rate in the termios struc‐
ture referenced by tp to speed.
The cfgetospeed() function returns the output baud rate in the termios
structure referenced by tp.
The cfsetospeed() function sets the output baud rate in the termios
structure referenced by tp to speed.
The cfsetspeed() function sets both the input and output baud rate in the
termios structure referenced by tp to speed.
Upon successful completion, the functions cfsetispeed(), cfsetospeed(),
and cfsetspeed() return a value of 0. Otherwise, a value of -1 is
returned and the global variable errno is set to indicate the error.
GETTING AND SETTING THE TERMIOS STATE
This section describes the functions that are used to control the general
terminal interface. Unless otherwise noted for a specific command, these
functions are restricted from use by background processes. Attempts to
perform these operations shall cause the process group to be sent a
SIGTTOU signal. If the calling process is blocking or ignoring SIGTTOU
signals, the process is allowed to perform the operation and the SIGTTOU
signal is not sent.
In all the functions, although fd is an open file descriptor, the func‐
tions affect the underlying terminal file, not just the open file
description associated with the particular file descriptor.
The cfmakeraw() function sets the flags stored in the termios structure
to a state disabling all input and output processing, giving a “raw I/O
path”. It should be noted that there is no function to reverse this
effect. This is because there are a variety of processing options that
could be re-enabled and the correct method is for an application to snap‐
shot the current terminal state using the function tcgetattr(), setting
raw mode with cfmakeraw() and the subsequent tcsetattr(), and then using
another tcsetattr() with the saved state to revert to the previous termi‐
nal state.
The tcgetattr() function copies the parameters associated with the termi‐
nal referenced by fd in the termios structure referenced by tp. This
function is allowed from a background process, however, the terminal
attributes may be subsequently changed by a foreground process.
The tcsetattr() function sets the parameters associated with the terminal
from the termios structure referenced by tp. The action field is created
by or'ing the following values, as specified in the include file
<termios.h>.
TCSANOW The change occurs immediately.
TCSADRAIN The change occurs after all output written to fd has been
transmitted to the terminal. This value of action should be
used when changing parameters that affect output.
TCSAFLUSH The change occurs after all output written to fd has been
transmitted to the terminal. Additionally, any input that has
been received but not read is discarded.
TCSASOFT If this value is or'ed into the action value, the values of
the c_cflag, c_ispeed, and c_ospeed fields are ignored.
The 0 baud rate is used to terminate the connection. If 0 is specified
as the output speed to the function tcsetattr(), modem control will no
longer be asserted on the terminal, disconnecting the terminal.
If zero is specified as the input speed to the function tcsetattr(), the
input baud rate will be set to the same value as that specified by the
output baud rate.
If tcsetattr() is unable to make any of the requested changes, it returns
-1 and sets errno. Otherwise, it makes all of the requested changes it
can. If the specified input and output baud rates differ and are a com‐
bination that is not supported, neither baud rate is changed.
Upon successful completion, the functions tcgetattr() and tcsetattr()
return a value of 0. Otherwise, they return -1 and the global variable
errno is set to indicate the error, as follows:
[EBADF] The fd argument to tcgetattr() or tcsetattr() was not
a valid file descriptor.
[EINTR] The tcsetattr() function was interrupted by a signal.
[EINVAL] The action argument to the tcsetattr() function was
not valid, or an attempt was made to change an
attribute represented in the termios structure to an
unsupported value.
[ENOTTY] The file associated with the fd argument to
tcgetattr() or tcsetattr() is not a terminal.
SEE ALSOtcsendbreak(3), termios(4)STANDARDS
The cfgetispeed(), cfsetispeed(), cfgetospeed(), cfsetospeed(),
tcgetattr() and tcsetattr() functions are expected to be compliant with
the IEEE Std 1003.1-1988 (“POSIX.1”) specification. The cfmakeraw() and
cfsetspeed() functions, as well as the TCSASOFT option to the tcsetattr()
function are extensions to the IEEE Std 1003.1-1988 (“POSIX.1”) specifi‐
cation.
BSD January 2, 1994 BSD
