TCSETATTR(3) BSD Library Functions Manual TCSETATTR(3)
cfgetispeed, cfsetispeed, cfgetospeed, cfsetospeed, cfsetspeed, cfmakeraw, tcgetattr, tcsetattr -- manipulating the termios structure
Standard C Library (libc, -lc)
cfgetispeed(const struct termios *t);
cfsetispeed(struct termios *t, speed_t speed);
cfgetospeed(const 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, const 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
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
#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 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.
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.
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.
May 1, 2004 BSD