trusty (3) tcgetattr.3posix.gz
NAME
tcgetattr - get the parameters associated with the terminal
SYNOPSIS
#include <termios.h> int tcgetattr(int fildes, struct termios *termios_p);
DESCRIPTION
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).
RETURN VALUE
Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno set to
indicate the error.
ERRORS
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.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
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(), changing only the necessary
fields. The application should use the values saved from the tcgetattr() to reset the terminal state
whenever it is done with the terminal. This is necessary 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 changes.
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.
FUTURE DIRECTIONS
None.
SEE ALSO
tcsetattr() , the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 11, General Terminal
Interface, <termios.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 .