TCSETATTR

Section: C Library Functions (3)
Index Return to Main Contents

BSD mandoc

NAME

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

SYNOPSIS

Fd #include <termios.h> Ft speed_t Fn cfgetispeed const struct termios *t Ft int Fn cfsetispeed struct termios *t speed_t speed Ft speed_t Fn cfgetospeed const struct termios *t Ft int Fn cfsetospeed struct termios *t speed_t speed Ft void Fn cfsetspeed struct termios *t speed_t speed Ft void Fn cfmakeraw struct termios *t Ft int Fn tcgetattr int fd struct termios *t Ft int Fn 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 Aq Pa 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 Fa tp .

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

The cfgetospeed function returns the output baud rate in the termios structure referenced by Fa tp .

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

The cfsetspeed function sets both the input and output baud rate in the termios structure referenced by Fa tp to Fa 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 Fa 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 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 Fa fd in the termios structure referenced by Fa 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 Fa tp . The Fa action field is created by or 'ing the following values, as specified in the include file Aq Pa termios.h .

Fa TCSANOW: The change occurs immediately.
Fa TCSADRAIN: The change occurs after all output written to Fa fd has been transmitted to the terminal. This value of Fa action should be used when changing parameters that affect output.
Fa TCSAFLUSH: The change occurs after all output written to Fa fd has been transmitted to the terminal Additionally, any input that has been received but not read is discarded.
Fa TCSASOFT: If this value is or 'ed into the Fa 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 able 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:

Bq Er EBADF: The Fa fd argument to tcgetattr or tcsetattr was not a valid file descriptor.
Bq Er EINTR: The tcsetattr function was interrupted by a signal.
Bq Er EINVAL: The Fa 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.
Bq Er ENOTTY: The file associated with the Fa fd argument to tcgetattr or tcsetattr is not a terminal.

STANDARDS

The cfgetispeed cfsetispeed cfgetospeed cfsetospeed tcgetattr and tcsetattr functions are expected to be compliant with the St -p1003.1-88 specification. The cfmakeraw and cfsetspeed functions, as well as the TCSASOFT option to the tcsetattr function are extensions to the St -p1003.1-88 specification.

Index

NAME
SYNOPSIS
DESCRIPTION
GETTING AND SETTING THE BAUD RATE
GETTING AND SETTING THE TERMIOS STATE
SEE ALSO
STANDARDS

This document was created by man2html, using the manual pages.
Time: 16:28:56 GMT, April 18, 2022