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



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

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  termi-
       nal.

       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 sup-
       ported,  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  tcge-
       tattr() 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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                 TCGETATTR(3P)