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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
.TH "TCGETATTR" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" tcgetattr
.SH 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.
.SH NAME
tcgetattr \- get the parameters associated with the terminal
.SH SYNOPSIS
.LP
\fB#include <termios.h>
.br
.sp
int tcgetattr(int\fP \fIfildes\fP\fB, struct termios *\fP\fItermios_p\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fItcgetattr\fP() function shall get the parameters associated
with the terminal referred to by \fIfildes\fP and store
them in the \fBtermios\fP structure referenced by \fItermios_p\fP.
The \fIfildes\fP argument is an open file descriptor
associated with a terminal.
.LP
The \fItermios_p\fP argument is a pointer to a \fBtermios\fP structure.
.LP
The \fItcgetattr\fP() operation is allowed from any process.
.LP
If the terminal device supports different input and output baud rates,
the baud rates stored in the \fBtermios\fP structure
returned by \fItcgetattr\fP() 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 \fBtermios\fP structure
shall be the output rate (as one of the symbolic
values).
.SH RETURN VALUE
.LP
Upon successful completion, 0 shall be returned. Otherwise, -1 shall
be returned and \fIerrno\fP set to indicate the error.
.SH ERRORS
.LP
The \fItcgetattr\fP() function shall fail if:
.TP 7
.B EBADF
The \fIfildes\fP argument is not a valid file descriptor.
.TP 7
.B ENOTTY
The file associated with \fIfildes\fP is not a terminal.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
Care must be taken when changing the terminal attributes. Applications
should always do a \fItcgetattr\fP(), save the
\fBtermios\fP structure values returned, and then do a \fItcsetattr\fP(),
changing only
the necessary fields. The application should use the values saved
from the \fItcgetattr\fP() 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.
.LP
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.
.LP
Existing practice dealing with error returns when only part of a request
can be honored is based on calls to the \fIioctl\fP() function. In
historical BSD and System V implementations, the corresponding \fIioctl\fP()
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.
.LP
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.
.LP
Applications that need all of the requested changes made to work properly
should follow \fItcsetattr\fP() with a call to \fItcgetattr\fP() and
compare the appropriate field
values.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fItcsetattr\fP(), the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
Chapter 11, General Terminal Interface, \fI<termios.h>\fP
.SH 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 .
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