TCSETATTR(3C) Standard C Library Functions TCSETATTR(3C)


tcsetattr - set the parameters associated with the terminal


#include <termios.h>

int tcsetattr(int fildes, int optional_actions,
const struct termios *termios_p);


The tcsetattr() function sets 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 (see termio(4I))
referenced by termios_p as follows:

o If optional_actions is TCSANOW, the change will occur

o If optional_actions is TCSADRAIN, the change will occur after
all output written to fildes is transmitted. This function
should be used when changing parameters that affect output.

o If optional_actions is TCSAFLUSH, the change will occur after
all output written to fildes is transmitted, and all input so
far received but not read will 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 will no
longer be asserted. Normally, this will 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 will be the
same as the output baud rate stored in the termios structure.

The tcsetattr() function will 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 will set all the attributes that
implementation supports as requested and leave all the attributes not
supported by the implementation unchanged. If no part of the request can
be honoured, it will 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 is changed. A subsequent call to tcgetattr(3C) will
return the actual state of the terminal device (reflecting both the
changes made and not made in the previous tcsetattr() call). The
tcsetattr() function will not change the values in the termios structure
whether or not it actually accepts them.

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(3C) on fildes; an application should modify only fields
and flags defined by this document between the call to tcgetattr(3C) and
tcsetattr(), leaving all other fields and flags unmodified.

No actions defined by this document, other than a call to tcsetattr() or
a close of the last file descriptor in the system associated with this
terminal device, will cause any of the terminal attributes defined by
this document to change.

Attempts to use tcsetattr() from a process which is a member of a
background process group on a fildes associated with its controlling
terminal, will 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 no signal is sent.


If trying to change baud rates, applications should call tcsetattr() then
call tcgetattr(3C) in order to determine what baud rates were actually


Upon successful completion, 0 is returned. Otherwise, -1 is returned and
errno is set to indicate the error.


The tcsetattr() function will fail if:

The fildes argument is not a valid file descriptor.

A signal interrupted tcsettattr().

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.

The file associated with fildes is not a terminal.

The tcsetattr() function may fail if:

The process group of the writing process is orphaned, and the
writing process is not ignoring or blocking SIGTTOU.


See attributes(7) for descriptions of the following attributes:

|Interface Stability | Standard |
|MT-Level | MT-Safe, and Async-Signal-Safe |


cfgetispeed(3C), tcgetattr(3C), termio(4I), attributes(7), standards(7)

August 14, 2002 TCSETATTR(3C)