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TCSETATTR(3) Library Functions Manual TCSETATTR(3)

cfgetispeed, cfsetispeed, cfgetospeed, cfsetospeed, cfsetspeed, cfmakeraw, tcgetattr, tcsetattr — manipulating the termios structure

#include <termios.h>

speed_t
cfgetispeed(const struct termios *tp);

int
cfsetispeed(struct termios *tp, speed_t speed);

speed_t
cfgetospeed(const struct termios *tp);

int
cfsetospeed(struct termios *tp, speed_t speed);

int
cfsetspeed(struct termios *tp, speed_t speed);

void
cfmakeraw(struct termios *tp);

int
tcgetattr(int fd, struct termios *tp);

int
tcsetattr(int fd, int action, const struct termios *tp);

The (), tcgetattr(), and tcsetattr() functions are provided for getting and setting the termios structure.

The (), 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.

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>. On OpenBSD, the value of the integer corresponds directly to the baud rate being represented. However, this is not true of all systems and new code should use the symbolic value for maximum portability.

#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 () function returns the input baud rate in the termios structure referenced by tp.

The () function sets the input baud rate in the termios structure referenced by tp to speed.

The () function returns the output baud rate in the termios structure referenced by tp.

The () function sets the output baud rate in the termios structure referenced by tp to speed.

The () function sets both the input and output baud rate in the termios structure referenced by tp to speed.

Upon successful completion, the functions (), 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.

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 () 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 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 () function copies the parameters associated with the terminal referenced by fd in the termios structure referenced by tp. This function is allowed from a background process, although the terminal attributes may be subsequently changed by a foreground process.

The () 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>.

The change occurs immediately.
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.
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.
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 (), modem control will no longer be asserted on the terminal, disconnecting the terminal.

If zero is specified as the input speed to the function (), 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:

[]
The fd argument to tcgetattr() or tcsetattr() was not a valid file descriptor.
[]
The tcsetattr() function was interrupted by a signal.
[]
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.
[]
The file associated with the fd argument to tcgetattr() or tcsetattr() is not a terminal.

tcsendbreak(3), termios(4)

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.

September 11, 2022 OpenBSD-7.2