TCSETATTR(3) BSD Library Functions Manual TCSETATTR(3)
NAME
cfgetispeed, cfgetospeed, cfmakeraw, cfsetispeed, cfsetospeed, cfsetspeed, tcgetattr, tcsetattr --manipulating -manipulating
manipulating the termios structure
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <termios.h>
speed_t
cfgetispeed(const struct termios *termios_p);
speed_t
cfgetospeed(const struct termios *termios_p);
void
cfmakeraw(struct termios *termios_p);
int
cfsetispeed(struct termios *termios_p, speed_t speed);
int
cfsetospeed(struct termios *termios_p, speed_t speed);
int
cfsetspeed(struct termios *termios_p, speed_t speed);
int
tcgetattr(int fildes, struct termios *termios_p);
int
tcsetattr(int fildes, int optional_actions, const struct termios *termios_p);
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. As described below, the effects
of the functions on the terminal 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 represented; 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_C_SOURCE
#define EXTA 19200
#define EXTB 38400
#endif /*_POSIX_C_SOURCE */
The cfgetispeed() function returns the input baud rate in the termios structure referenced by
termios_p.
The cfsetispeed() function sets the input baud rate in the termios structure referenced by termios_p to
speed.
The cfgetospeed() function returns the output baud rate in the termios structure referenced by
termios_p.
The cfsetospeed() function sets the output baud rate in the termios structure referenced by termios_p
to speed.
The cfsetspeed() function sets both the input and output baud rate in the termios structure referenced
by termios_p 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 pro-cesses. processes.
cesses. Attempts to perform these operations shall cause the process group to be sent a SIGTTOU sig-nal. signal.
nal. 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 of the functions, although fildes is an open file descriptor, the functions affect the underly-ing underlying
ing terminal file, not just the open file description that is 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. Because a variety of processing options could be re-enabled, the correct method
is for an application to snapshot 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 fildes in the
termios structure referenced by termios_p. This function is allowed from a background process; how-ever, however,
ever, 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 termios_p. The optional_actions 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 fildes has been transmitted to the terminal.
This value of optional_actions should be used when changing parameters that affect output.
TCSAFLUSH The change occurs after all output written to fildes 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 optional_actions 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 ter-minal. terminal.
minal.
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. Other-wise, Otherwise,
wise, it makes all of the requested changes it can. If the specified input and output baud rates dif-fer differ
fer and are a combination 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 fildes argument to tcgetattr() or tcsetattr() was not a valid file descriptor.
[EINTR] The tcsetattr() function was interrupted by a signal.
[EINVAL] The optional_actions 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 fildes argument to tcgetattr() or tcsetattr() is not a
terminal.
SEE ALSO
tcsendbreak(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 January 2, 1994 BSD
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