The termios Structure¶

The <termios.h> header shall define the following data types through typedef:

cc_t

Used for terminal special characters.

speed_t

Used for terminal baud rates.

tcflag_t

Used for terminal modes.

The above types shall be all unsigned integer types.

The implementation shall support one or more programming environments in which the widths of cc_t, speed_t, and tcflag_t are no greater than the width of type long. The names of these programming environments can be obtained using the confstr() function or the getconf utility.

The <termios.h> header shall define the termios structure, which shall include at least the following members:

tcflag_t  c_iflag     Input modes.
tcflag_t  c_oflag     Output modes.
tcflag_t  c_cflag     Control modes.
tcflag_t  c_lflag     Local modes.
cc_t      c_cc[NCCS]  Control characters.

The <termios.h> header shall define the following symbolic constant:

NCCS

Size of the array c_cc for control characters.

The <termios.h> header shall define the following symbolic constants for use as subscripts for the array c_cc:

The subscript values shall be suitable for use in #if preprocessing directives and shall be distinct, except that the VMIN and VTIME subscripts may have the same values as the VEOF and VEOL subscripts, respectively.

Input Modes¶

The <termios.h> header shall define the following symbolic constants for use as flags in the c_iflag field. The c_iflag field describes the basic terminal input control.

BRKINT

Signal interrupt on break.

ICRNL

Map CR to NL on input.

IGNBRK

Ignore break condition.

IGNCR

Ignore CR.

IGNPAR

Ignore characters with parity errors.

INLCR

Map NL to CR on input.

INPCK

Enable input parity check.

ISTRIP

Strip character.

IXANY

Enable any character to restart output.

IXOFF

Enable start/stop input control.

IXON

Enable start/stop output control.

PARMRK

Mark parity errors.

Output Modes¶

The <termios.h> header shall define the following symbolic constants for use as flags in the c_oflag field. The c_oflag field specifies the system treatment of output.

OPOST

Post-process output.

ONLCR

Map NL to CR-NL on output.

OCRNL

Map CR to NL on output.

ONOCR

No CR output at column 0.

ONLRET

NL performs CR function.

OFDEL

Fill is DEL.

OFILL

Use fill characters for delay.

NLDLY

Select newline delays:

CRDLY

Select carriage-return delays:

TABDLY

Select horizontal-tab delays:

BSDLY

Select backspace delays:

VTDLY

Select vertical-tab delays:

FFDLY

Select form-feed delays:

Baud Rate Selection¶

The <termios.h> header shall define the following symbolic constants for use as values of objects of type speed_t.

The input and output baud rates are stored in the termios structure. These are the valid values for objects of type speed_t. Not all baud rates need be supported by the underlying hardware.

B0

Hang up

B50

50 baud

B75

75 baud

B110

110 baud

B134

134.5 baud

B150

150 baud

B200

200 baud

B300

300 baud

B600

600 baud

B1200

1200 baud

B1800

1800 baud

B2400

2400 baud

B4800

4800 baud

B9600

9600 baud

B19200

19200 baud

B38400

38400 baud

Control Modes¶

The <termios.h> header shall define the following symbolic constants for use as flags in the c_cflag field. The c_cflag field describes the hardware control of the terminal; not all values specified are required to be supported by the underlying hardware.

CSIZE

Character size:

CSTOPB

Send two stop bits, else one.

CREAD

Enable receiver.

PARENB

Parity enable.

PARODD

Odd parity, else even.

HUPCL

Hang up on last close.

CLOCAL

Ignore modem status lines.

The implementation shall support the functionality associated with the symbols CS7, CS8, CSTOPB, PARODD, and PARENB.

Local Modes¶

The <termios.h> header shall define the following symbolic constants for use as flags in the c_lflag field. The c_lflag field of the argument structure is used to control various terminal functions.

ECHO

Enable echo.

ECHOE

Echo erase character as error-correcting backspace.

ECHOK

Echo KILL.

ECHONL

Echo NL.

ICANON

Canonical input (erase and kill processing).

IEXTEN

Enable extended input character processing.

ISIG

Enable signals.

NOFLSH

Disable flush after interrupt or quit.

TOSTOP

Send SIGTTOU for background output.

Attribute Selection¶

The <termios.h> header shall define the following symbolic constants for use with tcsetattr():

TCSANOW

Change attributes immediately.

TCSADRAIN

Change attributes when output has drained.

TCSAFLUSH

Change attributes when output has drained; also flush pending input.

Line Control¶

The <termios.h> header shall define the following symbolic constants for use with tcflush():

TCIFLUSH

Flush pending input.

TCIOFLUSH

Flush both pending input and untransmitted output.

TCOFLUSH

Flush untransmitted output.

The <termios.h> header shall define the following symbolic constants for use with tcflow():

TCIOFF

Transmit a STOP character, intended to suspend input data.

TCION

Transmit a START character, intended to restart input data.

TCOOFF

Suspend output.

TCOON

Restart output.

The <termios.h> header shall define the pid_t type as described in <sys/types.h>.

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

speed_t cfgetispeed(const struct termios *);
speed_t cfgetospeed(const struct termios *);
int     cfsetispeed(struct termios *, speed_t);
int     cfsetospeed(struct termios *, speed_t);
int     tcdrain(int);
int     tcflow(int, int);
int     tcflush(int, int);
int     tcgetattr(int, struct termios *);
pid_t   tcgetsid(int);
int     tcsendbreak(int, int);
int     tcsetattr(int, int, const struct termios *);

The following sections are informative.