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 typdef'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_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 structure 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 functions 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 (initialized by
tcgetattr) 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 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
fd to 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.
RETURN VALUES
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
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 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 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.