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.

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 POSIX.1‐2017 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 POSIX.1‐2017 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
       POSIX.1‐2017 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  POSIX.1‐2017,  Chapter  11,  General  Terminal  Interface,
       <termios.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any  typographical  or  formatting errors that appear in this page are most likely to have
       been introduced during the conversion of the source files to man page  format.  To  report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .