TCGETATTR(P) POSIX Programmer's Manual TCGETATTR(P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAMEtcgetattr - 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 descrip‐
tor 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 differ‐
ing 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 tcge‐
tattr() to reset the terminal state whenever it is done with the termi‐
nal. This is necessary because terminal attributes apply to the under‐
lying port and not to each individual open instance; that is, all pro‐
cesses that have used the terminal see the latest attribute changes.
A program that uses these functions should be written to catch all sig‐
nals 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 prop‐
erly should follow tcsetattr() with a call to tcgetattr() and compare
the appropriate field values.
FUTURE DIRECTIONS
None.
SEE ALSOtcsetattr() , 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 .
IEEE/The Open Group 2003 TCGETATTR(P)
