TCGETATTR(P) POSIX Programmer's Manual TCGETATTR(P)
tcgetattr - get the parameters associated with the terminal
int tcgetattr(int fildes, struct termios *termios_p);
The tcgetattr() function shall get the parameters associated with the terminal referred to
by fildes and store them in the termios structure referenced by termios_p. The fildes
argument is an open file descriptor associated with a terminal.
The termios_p argument is a pointer to a termios structure.
The tcgetattr() operation is allowed from any process.
If the terminal device supports different input and output baud rates, the baud rates
stored in the termios structure returned by tcgetattr() shall reflect the actual baud
rates, even if they are equal. If differing baud rates are not supported, the rate
returned as the output baud rate shall be the actual baud rate. If the terminal device
does not support split baud rates, the input baud rate stored in the termios structure
shall be the output rate (as one of the symbolic values).
Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno
set to indicate the error.
The tcgetattr() function shall fail if:
EBADF The fildes argument is not a valid file descriptor.
ENOTTY The file associated with fildes is not a terminal.
The following sections are informative.
Care must be taken when changing the terminal attributes. Applications should always do a
tcgetattr(), save the termios structure values returned, and then do a tcsetattr(), chang-
ing only the necessary fields. The application should use the values saved from the tcge-
tattr() to reset the terminal state whenever it is done with the terminal. This is neces-
sary because terminal attributes apply to the underlying port and not to each individual
open instance; that is, all processes that have used the terminal see the latest attribute
A program that uses these functions should be written to catch all signals and take other
appropriate actions to ensure that when the program terminates, whether planned or not,
the terminal device's state is restored to its original state.
Existing practice dealing with error returns when only part of a request can be honored is
based on calls to the ioctl() function. In historical BSD and System V implementations,
the corresponding ioctl() returns zero if the requested actions were semantically correct,
even if some of the requested changes could not be made. Many existing applications assume
this behavior and would no longer work correctly if the return value were changed from
zero to -1 in this case.
Note that either specification has a problem. When zero is returned, it implies everything
succeeded even if some of the changes were not made. When -1 is returned, it implies
everything failed even though some of the changes were made.
Applications that need all of the requested changes made to work properly should follow
tcsetattr() with a call to tcgetattr() and compare the appropriate field values.
tcsetattr() , the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 11, General
Terminal Interface, <termios.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 TCGETATTR(P)