TCSETATTR(P) POSIX Programmer's Manual TCSETATTR(P)NAMEtcsetattr - set the parameters associated with the terminal
SYNOPSIS
#include <termios.h>
int tcsetattr(int fildes, int optional_actions,
const struct termios *termios_p);
DESCRIPTION
The tcsetattr() function shall set the parameters associated with the
terminal referred to by the open file descriptor fildes (an open file
descriptor associated with a terminal) from the termios structure ref‐
erenced by termios_p as follows:
* If optional_actions is TCSANOW, the change shall occur immediately.
* If optional_actions is TCSADRAIN, the change shall occur after all
output written to fildes is transmitted. This function should be
used when changing parameters that affect output.
* If optional_actions is TCSAFLUSH, the change shall occur after all
output written to fildes is transmitted, and all input so far
received but not read shall be discarded before the change is made.
If the output baud rate stored in the termios structure pointed to by
termios_p is the zero baud rate, B0, the modem control lines shall no
longer be asserted. Normally, this shall disconnect the line.
If the input baud rate stored in the termios structure pointed to by
termios_p is 0, the input baud rate given to the hardware is the same
as the output baud rate stored in the termios structure.
The tcsetattr() function shall return successfully if it was able to
perform any of the requested actions, even if some of the requested
actions could not be performed. It shall set all the attributes that
the implementation supports as requested and leave all the attributes
not supported by the implementation unchanged. If no part of the
request can be honored, it shall return -1 and set errno to [EINVAL].
If the input and output baud rates differ and are a combination that is
not supported, neither baud rate shall be changed. A subsequent call to
tcgetattr() shall return the actual state of the terminal device
(reflecting both the changes made and not made in the previous tcse‐
tattr() call). The tcsetattr() function shall not change the values
found in the termios structure under any circumstances.
The effect of tcsetattr() is undefined if the value of the termios
structure pointed to by termios_p was not derived from the result of a
call to tcgetattr() on fildes; an application should modify only fields
and flags defined by this volume of IEEE Std 1003.1-2001 between the
call to tcgetattr() and tcsetattr(), leaving all other fields and flags
unmodified.
No actions defined by this volume of IEEE Std 1003.1-2001, other than a
call to tcsetattr() or a close of the last file descriptor in the sys‐
tem associated with this terminal device, shall cause any of the termi‐
nal attributes defined by this volume of IEEE Std 1003.1-2001 to
change.
If tcsetattr() is called from a process which is a member of a back‐
ground process group on a fildes associated with its controlling termi‐
nal:
* If the calling process is blocking or ignoring SIGTTOU signals, the
operation completes normally and no signal is sent.
* Otherwise, a SIGTTOU signal shall be sent to the process group.
RETURN VALUE
Upon successful completion, 0 shall be returned. Otherwise, -1 shall be
returned and errno set to indicate the error.
ERRORS
The tcsetattr() function shall fail if:
EBADF The fildes argument is not a valid file descriptor.
EINTR A signal interrupted tcsetattr().
EINVAL The optional_actions argument is not a supported value, or an
attempt was made to change an attribute represented in the
termios structure to an unsupported value.
ENOTTY The file associated with fildes is not a terminal.
The tcsetattr() function may fail if:
EIO The process group of the writing process is orphaned, and the
writing process is not ignoring or blocking SIGTTOU.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
If trying to change baud rates, applications should call tcsetattr()
then call tcgetattr() in order to determine what baud rates were actu‐
ally selected.
RATIONALE
The tcsetattr() function can be interrupted in the following situa‐
tions:
* It is interrupted while waiting for output to drain.
* It is called from a process in a background process group and SIGT‐
TOU is caught.
See also the RATIONALE section in tcgetattr() .
FUTURE DIRECTIONS
Using an input baud rate of 0 to set the input rate equal to the output
rate may not necessarily be supported in a future version of this vol‐
ume of IEEE Std 1003.1-2001.
SEE ALSOcfgetispeed() , tcgetattr() , the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 11, General Terminal Interface,
<termios.h>, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 TCSETATTR(P)
