tcgetattr(3p) — Linux manual page


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

PROLOG         top

       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.

NAME         top

       tcgetattr — get the parameters associated with the terminal

SYNOPSIS         top

       #include <termios.h>

       int tcgetattr(int fildes, struct termios *termios_p);

DESCRIPTION         top

       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         top

       Upon successful completion, 0 shall be returned. Otherwise, -1
       shall be returned and errno set to indicate the error.

ERRORS         top

       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         top




RATIONALE         top

       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.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2017, Chapter 11, General
       Terminal Interface, termios.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017                     TCGETATTR(3P)

Pages that refer to this page: termios.h(0p)cfgetispeed(3p)cfgetospeed(3p)tcsetattr(3p)