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

NAME
       cfgetispeed - get input baud rate

SYNOPSIS
       #include <termios.h>

       speed_t cfgetispeed(const struct termios *termios_p);

DESCRIPTION
       The  cfgetispeed()  function shall extract the input baud rate from the
       termios structure to which the termios_p argument points.

       This function shall return exactly the value in the termios data struc‐
       ture, without interpretation.

RETURN VALUE
       Upon  successful completion, cfgetispeed() shall return a value of type
       speed_t representing the input baud rate.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       The term "baud" is used historically here, but is not technically  cor‐
       rect.  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.

       The  cfgetospeed(),  cfgetispeed(),  cfsetospeed(),  and	 cfsetispeed()
       functions do not take arguments as  numbers,  but  rather  as  symbolic
       names. There are two reasons for this:

	1. Historically, numbers were not used because of the way the rate was
	   stored in the data structure. This is retained even though a	 func‐
	   tion is now used.

	2. More	 importantly,  only  a limited set of possible rates is at all
	   portable, and this constrains the application to that set.

       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.

       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 con‐
       stant 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
       cfsetispeed() value is retained after a tcgetattr() as the actual value
       or  as  zero. Therefore, conforming applications should always set both
       the input speed and output speed when setting either.

       In historical implementations, the baud rate information is  tradition‐
       ally  kept  in  c_cflag. Applications should be written to presume that
       this might be the case (and thus not blindly copy c_cflag), but not  to
       rely  on it in case it is in some other field of the structure. Setting
       the c_cflag field absolutely after setting a baud rate is a  non-porta‐
       ble  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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       cfgetospeed()  , cfsetispeed() , cfsetospeed() , tcgetattr() , the Base
       Definitions volume of IEEE Std 1003.1-2001, Chapter 11, General	Termi‐
       nal 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 original Standard can be  obtained	online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group		     2003			CFGETISPEED(P)
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