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 structure, 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 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.

       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 function 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 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 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 traditionally 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-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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       cfgetospeed()  ,  cfsetispeed()  ,  cfsetospeed()  ,  tcgetattr()  ,  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
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                        CFGETISPEED(P)