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 .