TCSETATTR(3) BSD Library Functions Manual TCSETATTR(3)NAME
cfgetispeed, cfsetispeed, cfgetospeed, cfsetospeed, cfsetspeed,
cfmakeraw, tcgetattr, tcsetattr — manipulating the termios structure
cfgetispeed(struct termios *t);
cfsetispeed(struct termios *t, speed_t speed);
cfgetospeed(struct termios *t);
cfsetospeed(struct termios *t, speed_t speed);
cfsetspeed(struct termios *t, speed_t speed);
cfmakeraw(struct termios *t);
tcgetattr(int fd, struct termios *t);
tcsetattr(int fd, int action, struct termios *t);
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 mean‐
ings. 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 typdef'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
#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 struc‐
ture 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 SIGT‐
TOU signal. If the calling process is blocking or ignoring SIGTTOU sig‐
nals, 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 terminal state.
The tcgetattr function copies the parameters associated with the terminal
referenced by fd in the termios structure referenced by tp. This func‐
tion 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
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
[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”) specification.
BSD November 17, 2018 BSD