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
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 (see 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 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
— Macro: tcflag_t PARENB
If this bit is set, generation and detection of a parity bit are enabled.
See 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
— Macro: tcflag_t CRTS_IFLOW
If this bit is set, enable flow control of input based on the RTS wire
— 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
This bit is never set in the structure filled in by tcgetattr.
Published under the terms of the GNU General Public License