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(libc.info)Control Modes

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Control Modes
-------------

   This section describes the terminal flags and fields that control
parameters usually associated with asynchronous serial data
transmission.  These flags may not make sense for other kinds of
terminal ports (such as a network connection pseudo-terminal).  All of
these are contained in the `c_cflag' member of the `struct termios'
structure.

   The `c_cflag' member itself is an integer, and you change the flags
and fields using the operators `&', `|', and `^'.  Don't try to specify
the entire value for `c_cflag'--instead, change only specific flags and
leave the rest untouched (Note: Setting Modes).

 - Macro: tcflag_t CLOCAL
     If this bit is set, it indicates that the terminal is connected
     "locally" and that the modem status lines (such as carrier detect)
     should be ignored.

     On many systems if this bit is not set and you call `open' without
     the `O_NONBLOCK' flag set, `open' blocks until a modem connection
     is established.

     If this bit is not set and a modem disconnect is detected, a
     `SIGHUP' signal is sent to the controlling process group for the
     terminal (if it has one).  Normally, this causes the process to
     exit; see Note: Signal Handling.  Reading from the terminal
     after a disconnect causes an end-of-file condition, and writing
     causes an `EIO' error to be returned.  The terminal device must be
     closed and reopened to clear the condition.

 - Macro: tcflag_t HUPCL
     If this bit is set, a modem disconnect is generated when all
     processes that have the terminal device open have either closed
     the file or exited.

 - Macro: tcflag_t CREAD
     If this bit is set, input can be read from the terminal.
     Otherwise, input is discarded when it arrives.

 - Macro: tcflag_t CSTOPB
     If this bit is set, two stop bits are used.  Otherwise, only one
     stop bit is used.

 - Macro: tcflag_t PARENB
     If this bit is set, generation and detection of a parity bit are
     enabled.  Note: Input Modes, for information on how input parity
     errors are handled.

     If this bit is not set, no parity bit is added to output
     characters, and input characters are not checked for correct
     parity.

 - Macro: tcflag_t PARODD
     This bit is only useful if `PARENB' is set.  If `PARODD' is set,
     odd parity is used, otherwise even parity is used.

   The control mode flags also includes a field for the number of bits
per character.  You can use the `CSIZE' macro as a mask to extract the
value, like this: `settings.c_cflag & CSIZE'.

 - Macro: tcflag_t CSIZE
     This is a mask for the number of bits per character.

 - Macro: tcflag_t CS5
     This specifies five bits per byte.

 - Macro: tcflag_t CS6
     This specifies six bits per byte.

 - Macro: tcflag_t CS7
     This specifies seven bits per byte.

 - Macro: tcflag_t CS8
     This specifies eight bits per byte.

   The following four bits are BSD extensions; this exist only on BSD
systems and the GNU system.

 - Macro: tcflag_t CCTS_OFLOW
     If this bit is set, enable flow control of output based on the CTS
     wire (RS232 protocol).

 - Macro: tcflag_t CRTS_IFLOW
     If this bit is set, enable flow control of input based on the RTS
     wire (RS232 protocol).

 - Macro: tcflag_t MDMBUF
     If this bit is set, enable carrier-based flow control of output.

 - Macro: tcflag_t CIGNORE
     If this bit is set, it says to ignore the control modes and line
     speed values entirely.  This is only meaningful in a call to
     `tcsetattr'.

     The `c_cflag' member and the line speed values returned by
     `cfgetispeed' and `cfgetospeed' will be unaffected by the call.
     `CIGNORE' is useful if you want to set all the software modes in
     the other members, but leave the hardware details in `c_cflag'
     unchanged.  (This is how the `TCSASOFT' flag to `tcsettattr'
     works.)

     This bit is never set in the structure filled in by `tcgetattr'.