TCGETATTR(3)               POSIX Programmer's Manual              TCGETATTR(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 POSIX.1-2017, Chapter 11, General
       Terminal Interface, <termios.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                         TCGETATTR(3)
