Input modes

The c_iflag field describes the basic terminal input control:

Mask name	Definition
BRKINT	Send SIGINT signal on break
ICRNL	Map CR to NL on input
IGNBRK	Ignore break
IGNCR	Ignore CR
IGNPAR	Ignore characters with parity errors
INLCR	Map NL to CR on input
INPCK	Enable input parity check
ISTRIP	Strip 8th bit of input character
IXOFF	Enable START/STOP input control
IXON	Enable START/STOP output control
PARMRK	Mark parity errors
IUCLC Will no longer be supported by the X/Open-Standard in future.	Map uppercase to lowercase on input
IXANY	Enable any input character to restart output

In the context of asynchronous serial transmission via a serial interface, a break is defined as a sequence of zero-valued bits that continues for more than the time required to send one byte. The entire sequence of zero-valued bits is interpreted as a single break, even if the sequence comprises more than one byte. In contexts other than asynchronous serial data transmission, the meaning of a break condition is not defined.

If IGNBRK is set, any break that occurs on input will be ignored, i.e. not placed in the input queue and therefore not read by any process. On the other hand, if BRKINT is set, the break condition generates a single interrupt signal SIGINT and flushes both the input and output queues. If neither IGNBRK nor BRKINT is set, a break condition is read as a single \0 character, or if PARMRK is set, as \377, \0, \0.

If IGNPAR is set, any byte with a character or parity error (other than break) is ignored.

If PARMRK is set, and IGNPAR is not set, any byte with a framing or parity error (other than break) is passed to the application as the three-character sequence \377, \0 and X, where \377 and \0 constitute a two-byte flag preceding each sequence and X corresponds to the character received in error. To avoid ambiguity in this case, if ISTRIP is not set, a valid character of \377 is passed to the application as \377, \377. If neither PARMRK nor IGNPAR is set, a framing or parity error (other than break) is passed to the application as a single

If INPCK is set, input parity checking is enabled. If INPCK is not set, input parity checking is disabled, allowing generation of the output parity bit without heeding any input parity errors that may have occurred.

Note

The enabling or disabling of input parity checking is independent of whether parity detection is enabled or disabled (see section “Control modes”). If parity detection is enabled but input parity checking is disabled, the hardware to which the terminal is connected will recognize the parity bit, but the terminal special file will not check whether or not this bit is correctly set.

If INLCR is set, a received NL character (newline) is translated into a CR character (carriage return). If IGNCR is set, a received CR character is ignored (not read). However, if IGNCR is not set and ICRNL is set, a received CR character is converted into an NL character.

If IUCLC is set, a received uppercase letter is mapped to the corresponding lowercase letter (Will no longer be supported by the X/Open-Standard in future.).

If IXON is set, START/STOP output control is enabled. A received STOP character suspends output, and a received START character restarts output. The control characters for START and STOP are not read during a read operation, however, they perform flow control functions when IXON is set. When IXON is not set, the START and STOP characters are read. If IXANY is set, the suspended output is resumed as soon as any character is entered.

If IXOFF is set, START/STOP input flow control is enabled. The system transmits STOP characters in order to cause the terminal device to stop transmitting data as needed to prevent an overflow in the input queue (no more than {MAX_INPUT} bytes are permitted). It transmits START characters to cause the terminal device to resume transmitting data, as soon as the device can continue doing so without any risk of overflowing the input queue.

The initial value for all input modes after an open() is that no flag is set.