This section describes the terminal attribute flags that control fairly low-level aspects of input processing: handling of parity errors, break signals, flow control, and RET and LFD characters.
All of these flags are bits in the
c_iflag member of the
struct termios structure. The member is an integer, and you
change flags using the operators
try to specify the entire value for
only specific flags and leave the rest untouched (see Setting Terminal Modes Properly).
If this bit is set, input parity checking is enabled. If it is not set, no checking at all is done for parity errors on input; the characters are simply passed through to the application.
Parity checking on input processing is independent of whether parity
detection and generation on the underlying terminal hardware is enabled;
see Control Modes. For example, you could clear the
input mode flag and set the
PARENB control mode flag to ignore
parity errors on input, but still generate parity on output.
If this bit is set, what happens when a parity error is detected depends
on whether the
PARMRK bits are set. If neither
of these bits are set, a byte with a parity error is passed to the
application as a
If this bit is set, any byte with a framing or parity error is ignored.
This is only useful if
INPCK is also set.
If this bit is set, input bytes with parity or framing errors are marked
when passed to the program. This bit is meaningful only when
INPCK is set and
IGNPAR is not set.
The way erroneous bytes are marked is with two preceding bytes,
0. Thus, the program actually reads three bytes
for one erroneous byte received from the terminal.
If a valid byte has the value
ISTRIP (see below)
is not set, the program might confuse it with the prefix that marks a
parity error. So a valid byte
0377 is passed to the program as
0377, in this case.
If this bit is set, valid input bytes are stripped to seven bits; otherwise, all eight bits are available for programs to read.
If this bit is set, break conditions are ignored.
A break condition is defined in the context of asynchronous serial data transmission as a series of zero-value bits longer than a single byte.
If this bit is set and
IGNBRK is not set, a break condition
clears the terminal input and output queues and raises a
signal for the foreground process group associated with the terminal.
IGNBRK are set, a break condition is
passed to the application as a single
'\0' character if
PARMRK is not set, or otherwise as a three-character sequence
If this bit is set, carriage return characters (
discarded on input. Discarding carriage return may be useful on
terminals that send both carriage return and linefeed when you type the
If this bit is set and
IGNCR is not set, carriage return characters
'\r') received as input are passed to the application as newline
If this bit is set, newline characters (
'\n') received as input
are passed to the application as carriage return characters (
If this bit is set, start/stop control on input is enabled. In other words, the computer sends STOP and START characters as necessary to prevent input from coming in faster than programs are reading it. The idea is that the actual terminal hardware that is generating the input data responds to a STOP character by suspending transmission, and to a START character by resuming transmission. See Special Characters for Flow Control.
If this bit is set, start/stop control on output is enabled. In other words, if the computer receives a STOP character, it suspends output until a START character is received. In this case, the STOP and START characters are never passed to the application program. If this bit is not set, then START and STOP can be read as ordinary characters. See Special Characters for Flow Control.
If this bit is set, any input character restarts output when output has been suspended with the STOP character. Otherwise, only the START character restarts output.
This is a BSD extension; it exists only on BSD systems and GNU/Linux and GNU/Hurd systems.
If this bit is set, then filling up the terminal input buffer sends a
BEL character (code
007) to the terminal to ring the bell.
This is a BSD extension.