man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

tcsetattr(3C)

Name

tcsetattr - 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 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(7I)) referenced by termios_p as follows:

  • If optional_actions is TCSANOW, the change will occur immediately.

  • 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.

  • 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.

Usage

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

Return Values

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

Errors

The tcsetattr() function will fail if:

EBADF

The fildes argument is not a valid file descriptor.

EINTR

A signal interrupted tcsettattr().

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.

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
MT-Safe, and Async-Signal-Safe
Standard

See Also

cfgetispeed(3C), tcgetattr(3C), attributes(5), standards(5) , termio(7I)