.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "CFGETISPEED" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" cfgetispeed 
.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
cfgetispeed \- get input baud rate
.SH SYNOPSIS
.LP
\fB#include <termios.h>
.br
.sp
speed_t cfgetispeed(const struct termios *\fP\fItermios_p\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fIcfgetispeed\fP() function shall extract the input baud rate
from the \fBtermios\fP structure to which the
\fItermios_p\fP argument points.
.LP
This function shall return exactly the value in the \fBtermios\fP
data structure, without interpretation.
.SH RETURN VALUE
.LP
Upon successful completion, \fIcfgetispeed\fP() shall return a value
of type \fBspeed_t\fP representing the input baud
rate.
.SH ERRORS
.LP
No errors are defined.
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
The term "baud" is used historically here, but is not technically
correct. This is properly "bits per second", which may not
be the same as baud. However, the term is used because of the historical
usage and understanding.
.LP
The \fIcfgetospeed\fP(), \fIcfgetispeed\fP(), \fIcfsetospeed\fP(),
and \fIcfsetispeed\fP()
functions do not take arguments as numbers, but rather as symbolic
names. There are two reasons for this:
.IP " 1." 4
Historically, numbers were not used because of the way the rate was
stored in the data structure. This is retained even though a
function is now used.
.LP
.IP " 2." 4
More importantly, only a limited set of possible rates is at all portable,
and this constrains the application to that set.
.LP
.LP
There is nothing to prevent an implementation accepting as an extension
a number (such as 126), and since the encoding of the
Bxxx symbols is not specified, this can be done to avoid introducing
ambiguity.
.LP
Setting the input baud rate to zero was a mechanism to allow for split
baud rates. Clarifications in this volume of
IEEE\ Std\ 1003.1-2001 have made it possible to determine whether
split rates are supported and to support them without
having to treat zero as a special case. Since this functionality is
also confusing, it has been declared obsolescent. The 0
argument referred to is the literal constant 0, not the symbolic constant
B0. This volume of IEEE\ Std\ 1003.1-2001 does
not preclude B0 from being defined as the value 0; in fact, implementations
would likely benefit from the two being equivalent.
This volume of IEEE\ Std\ 1003.1-2001 does not fully specify whether
the previous \fIcfsetispeed\fP() value is retained after a \fItcgetattr\fP()
as the actual value or as zero. Therefore, conforming applications
should
always set both the input speed and output speed when setting either.
.LP
In historical implementations, the baud rate information is traditionally
kept in \fBc_cflag\fP. Applications should be written
to presume that this might be the case (and thus not blindly copy
\fBc_cflag\fP), but not to rely on it in case it is in some
other field of the structure. Setting the \fBc_cflag\fP field absolutely
after setting a baud rate is a non-portable action
because of this. In general, the unused parts of the flag fields might
be used by the implementation and should not be blindly
copied from the descriptions of one terminal device to another.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIcfgetospeed\fP(), \fIcfsetispeed\fP(), \fIcfsetospeed\fP(),
\fItcgetattr\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 .