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Linux 2.6 - man page for tcgetattr (linux section 3posix)

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

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(), chang-
       ing  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 terminal. This is  neces-
       sary  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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				     TCGETATTR(P)


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