tcflush - phpMan

TERMIOS(3) Linux Programmer’s Manual TERMIOS(3)

NAME
termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfmakeraw,
cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed - get and set terminal
attributes, line control, get and set baud rate

SYNOPSIS
#include <termios.h>
#include <unistd.h>

int tcgetattr(int fd, struct termios *termios_p);

int tcsetattr(int fd, int optional_actions, struct termios *termios_p);

int tcsendbreak(int fd, int duration);

int tcdrain(int fd);

int tcflush(int fd, int queue_selector);

int tcflow(int fd, int action);

int cfmakeraw(struct termios *termios_p);

speed_t cfgetispeed(struct termios *termios_p);

speed_t cfgetospeed(struct termios *termios_p);

int cfsetispeed(struct termios *termios_p, speed_t speed);

int cfsetospeed(struct termios *termios_p, speed_t speed);

DESCRIPTION
The termios functions describe a general terminal interface that is provided to
control asynchronous communications ports.

Many of the functions described here have a termios_p argument that is a pointer to
a termios structure. This structure contains 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 chars */

c_iflag flag constants:

IGNBRK Ignore BREAK condition on input.

BRKINT If IGNBRK is set, a BREAK is ignored. If it is not set but BRKINT is set,
then a BREAK causes the input and output queues to be flushed, and if the
terminal is the controlling terminal of a foreground process group, it will
cause a SIGINT to be sent to this foreground process group. When neither
IGNBRK nor BRKINT are set, a BREAK reads as a NUL character, except when
PARMRK is set, in which case it reads as the sequence \377 \0 \0.

IGNPAR Ignore framing errors and parity errors.

PARMRK If IGNPAR is not set, prefix a character with a parity error or framing
error with \377 \0. If neither IGNPAR nor PARMRK is set, read a character
with a parity error or framing error as \0.

INPCK Enable input parity checking.

ISTRIP Strip off eighth bit.

INLCR Translate NL to CR on input.

IGNCR Ignore carriage return on input.

ICRNL Translate carriage return to newline on input (unless IGNCR is set).

IUCLC (not in POSIX) Map uppercase characters to lowercase on input.

IXON Enable XON/XOFF flow control on output.

IXANY (not in POSIX.1; XSI) Enable any character to restart output.

IXOFF Enable XON/XOFF flow control on input.

IMAXBEL
(not in POSIX) Ring bell when input queue is full. Linux does not implement
this bit, and acts as if it is always set.

c_oflag flag constants defined in POSIX.1:

OPOST Enable implementation-defined output processing.

The remaining c_oflag flag constants are defined in POSIX 1003.1-2001, unless
marked otherwise.

OLCUC (not in POSIX) Map lowercase characters to uppercase on output.

ONLCR (XSI) Map NL to CR-NL on output.

OCRNL Map CR to NL on output.

ONOCR Don’t output CR at column 0.

ONLRET Don’t output CR.

OFILL Send fill characters for a delay, rather than using a timed delay.

OFDEL (not in POSIX) Fill character is ASCII DEL (0177). If unset, fill character
is ASCII NUL.

NLDLY Newline delay mask. Values are NL0 and NL1.

CRDLY Carriage return delay mask. Values are CR0, CR1, CR2, or CR3.

TABDLY Horizontal tab delay mask. Values are TAB0, TAB1, TAB2, TAB3 (or XTABS). A
value of TAB3, that is, XTABS, expands tabs to spaces (with tab stops every
eight columns).

BSDLY Backspace delay mask. Values are BS0 or BS1. (Has never been implemented.)

VTDLY Vertical tab delay mask. Values are VT0 or VT1.

FFDLY Form feed delay mask. Values are FF0 or FF1.

c_cflag flag constants:

CBAUD (not in POSIX) Baud speed mask (4+1 bits).

CBAUDEX
(not in POSIX) Extra baud speed mask (1 bit), included in CBAUD.

(POSIX says that the baud speed is stored in the termios structure without specify-
ing where precisely, and provides cfgetispeed() and cfsetispeed() for getting at
it. Some systems use bits selected by CBAUD in c_cflag, other systems use separate
fields, e.g. sg_ispeed and sg_ospeed.)

CSIZE Character size mask. Values are CS5, CS6, CS7, or CS8.

CSTOPB Set two stop bits, rather than one.

CREAD Enable receiver.

PARENB Enable parity generation on output and parity checking for input.

PARODD Parity for input and output is odd.

HUPCL Lower modem control lines after last process closes the device (hang up).

CLOCAL Ignore modem control lines.

LOBLK (not in POSIX) Block output from a noncurrent shell layer. (For use by
shl.)

CIBAUD (not in POSIX) Mask for input speeds. The values for the CIBAUD bits are the
same as the values for the CBAUD bits, shifted left IBSHIFT bits.

CRTSCTS
(not in POSIX) Enable RTS/CTS (hardware) flow control.

c_lflag flag constants:

ISIG When any of the characters INTR, QUIT, SUSP, or DSUSP are received, generate
the corresponding signal.

ICANON Enable canonical mode. This enables the special characters EOF, EOL, EOL2,
ERASE, KILL, LNEXT, REPRINT, STATUS, and WERASE, and buffers by lines.

XCASE (not in POSIX; not supported under Linux) If ICANON is also set, terminal is
uppercase only. Input is converted to lowercase, except for characters pre-
ceded by \. On output, uppercase characters are preceded by \ and lowercase
characters are converted to uppercase.

ECHO Echo input characters.

ECHOE If ICANON is also set, the ERASE character erases the preceding input char-
acter, and WERASE erases the preceding word.

ECHOK If ICANON is also set, the KILL character erases the current line.

ECHONL If ICANON is also set, echo the NL character even if ECHO is not set.

ECHOCTL
(not in POSIX) If ECHO is also set, ASCII control signals other than TAB,
NL, START, and STOP are echoed as ^X, where X is the character with ASCII
code 0x40 greater than the control signal. For example, character 0x08 (BS)
is echoed as ^H.

ECHOPRT
(not in POSIX) If ICANON and IECHO are also set, characters are printed as
they are being erased.

ECHOKE (not in POSIX) If ICANON is also set, KILL is echoed by erasing each charac-
ter on the line, as specified by ECHOE and ECHOPRT.

DEFECHO
(not in POSIX) Echo only when a process is reading.

FLUSHO (not in POSIX; not supported under Linux) Output is being flushed. This
flag is toggled by typing the DISCARD character.

NOFLSH Disable flushing the input and output queues when generating the SIGINT,
SIGQUIT and SIGSUSP signals.

TOSTOP Send the SIGTTOU signal to the process group of a background process which
tries to write to its controlling terminal.

PENDIN (not in POSIX; not supported under Linux) All characters in the input queue
are reprinted when the next character is read. (bash handles typeahead this
way.)

IEXTEN Enable implementation-defined input processing. This flag, as well as
ICANON must be enabled for the special characters EOL2, LNEXT, REPRINT,
WERASE to be interpreted, and for the IUCLC flag to be effective.

The c_cc array defines the special control characters. The symbolic indices (ini-
tial values) and meaning are:

VINTR (003, ETX, Ctrl-C, or also 0177, DEL, rubout) Interrupt character. Send a
SIGINT signal. Recognized when ISIG is set, and then not passed as input.

VQUIT (034, FS, Ctrl-\) Quit character. Send SIGQUIT signal. Recognized when ISIG
is set, and then not passed as input.

VERASE (0177, DEL, rubout, or 010, BS, Ctrl-H, or also #) Erase character. This
erases the previous not-yet-erased character, but does not erase past EOF or
beginning-of-line. Recognized when ICANON is set, and then not passed as
input.

VKILL (025, NAK, Ctrl-U, or Ctrl-X, or also @) Kill character. This erases the
input since the last EOF or beginning-of-line. Recognized when ICANON is
set, and then not passed as input.

VEOF (004, EOT, Ctrl-D) End-of-file character. More precisely: this character
causes the pending tty buffer to be sent to the waiting user program without
waiting for end-of-line. If it is the first character of the line, the
read() in the user program returns 0, which signifies end-of-file. Recog-
nized when ICANON is set, and then not passed as input.

VMIN Minimum number of characters for non-canonical read.

VEOL (0, NUL) Additional end-of-line character. Recognized when ICANON is set.

VTIME Timeout in deciseconds for non-canonical read.

VEOL2 (not in POSIX; 0, NUL) Yet another end-of-line character. Recognized when
ICANON is set.

VSWTCH (not in POSIX; not supported under Linux; 0, NUL) Switch character. (Used by
shl only.)

VSTART (021, DC1, Ctrl-Q) Start character. Restarts output stopped by the Stop
character. Recognized when IXON is set, and then not passed as input.

VSTOP (023, DC3, Ctrl-S) Stop character. Stop output until Start character typed.
Recognized when IXON is set, and then not passed as input.

VSUSP (032, SUB, Ctrl-Z) Suspend character. Send SIGTSTP signal. Recognized when
ISIG is set, and then not passed as input.

VDSUSP (not in POSIX; not supported under Linux; 031, EM, Ctrl-Y) Delayed suspend
character: send SIGTSTP signal when the character is read by the user pro-
gram. Recognized when IEXTEN and ISIG are set, and the system supports job
control, and then not passed as input.

VLNEXT (not in POSIX; 026, SYN, Ctrl-V) Literal next. Quotes the next input charac-
ter, depriving it of a possible special meaning. Recognized when IEXTEN is
set, and then not passed as input.

VWERASE
(not in POSIX; 027, ETB, Ctrl-W) Word erase. Recognized when ICANON and
IEXTEN are set, and then not passed as input.

VREPRINT
(not in POSIX; 022, DC2, Ctrl-R) Reprint unread characters. Recognized when
ICANON and IEXTEN are set, and then not passed as input.

VDISCARD
(not in POSIX; not supported under Linux; 017, SI, Ctrl-O) Toggle:
start/stop discarding pending output. Recognized when IEXTEN is set, and
then not passed as input.

VSTATUS
(not in POSIX; not supported under Linux; status request: 024, DC4, Ctrl-T).

These symbolic subscript values are all different, except that VTIME, VMIN may have
the same value as VEOL, VEOF, respectively. (In non-canonical mode the special
character meaning is replaced by the timeout meaning. MIN represents the minimum
number of characters that should be received to satisfy the read. TIME is a
decisecond-valued timer. When both are set, a read will wait until at least one
character has been received, and then return as soon as either MIN characters have
been received or time TIME has passed since the last character was received. If
only MIN is set, the read will not return before MIN characters have been received.
If only TIME is set, the read will return as soon as either at least one character
has been received, or the timer times out. If neither is set, the read will return
immediately, only giving the currently already available characters.)

tcgetattr() gets the parameters associated with the object referred by fd and
stores them in the termios structure referenced by termios_p. This function may be
invoked from a background process; however, the terminal attributes may be subse-
quently changed by a foreground process.

tcsetattr() sets the parameters associated with the terminal (unless support is
required from the underlying hardware that is not available) from the termios
structure referred to by termios_p. optional_actions specifies when the changes
take effect:

TCSANOW
the change occurs immediately.

TCSADRAIN
the change occurs after all output written to fd has been transmitted. This
function should be used when changing parameters that affect output.

TCSAFLUSH
the change occurs after all output written to the object referred by fd has
been transmitted, and all input that has been received but not read will be
discarded before the change is made.

tcsendbreak() transmits a continuous stream of zero-valued bits for a specific
duration, if the terminal is using asynchronous serial data transmission. If dura-
tion is zero, it transmits zero-valued bits for at least 0.25 seconds, and not more
that 0.5 seconds. If duration is not zero, it sends zero-valued bits for some
implementation-defined length of time.

If the terminal is not using asynchronous serial data transmission, tcsendbreak()
returns without taking any action.

tcdrain() waits until all output written to the object referred to by fd has been
transmitted.

tcflush() discards data written to the object referred to by fd but not transmit-
ted, or data received but not read, depending on the value of queue_selector:

TCIFLUSH
flushes data received but not read.

TCOFLUSH
flushes data written but not transmitted.

TCIOFLUSH
flushes both data received but not read, and data written but not transmit-
ted.

tcflow() suspends transmission or reception of data on the object referred to by
fd, depending on the value of action:

TCOOFF suspends output.

TCOON restarts suspended output.

TCIOFF transmits a STOP character, which stops the terminal device from transmit-
ting data to the system.

TCION transmits a START character, which starts the terminal device transmitting
data to the system.

The default on open of a terminal file is that neither its input nor its output is
suspended.

The baud rate functions are provided for getting and setting the values of the
input and output baud rates in the termios structure. The new values do not take
effect until tcsetattr() is successfully called.

Setting the speed to B0 instructs the modem to "hang up". The actual bit rate cor-
responding to B38400 may be altered with setserial(8).

The input and output baud rates are stored in the termios structure.

cfgetospeed() returns the output baud rate stored in the termios structure pointed
to by termios_p.

cfsetospeed() sets the output baud rate stored in the termios structure pointed to
by termios_p to speed, which must be one of these constants:
B0
B50
B75
B110
B134
B150
B200
B300
B600
B1200
B1800
B2400
B4800
B9600
B19200
B38400
B57600
B115200
B230400
The zero baud rate, B0, is used to terminate the connection. If B0 is specified,
the modem control lines shall no longer be asserted. Normally, this will discon-
nect the line. CBAUDEX is a mask for the speeds beyond those defined in POSIX.1
(57600 and above). Thus, B57600 & CBAUDEX is nonzero.

cfgetispeed() returns the input baud rate stored in the termios structure.

cfsetispeed() sets the input baud rate stored in the termios structure to speed.
If the input baud rate is set to zero, the input baud rate will be equal to the
output baud rate.

RETURN VALUE
cfgetispeed() returns the input baud rate stored in the termios structure.

cfgetospeed() returns the output baud rate stored in the termios structure.

All other functions return:

0 on success.

-1 on failure and set errno to indicate the error.

Note that tcsetattr() returns success if any of the requested changes could be suc-
cessfully carried out. Therefore, when making multiple changes it may be necessary
to follow this call with a further call to tcgetattr() to check that all changes
have been performed successfully.

NOTES
Unix V7 and several later systems have a list of baud rates where after the four-
teen values B0, ..., B9600 one finds the two constants EXTA, EXTB ("External A" and
"External B"). Many systems extend the list with much higher baud rates.

The effect of a nonzero duration with tcsendbreak varies. SunOS specifies a break
of duration*N seconds, where N is at least 0.25, and not more than 0.5. Linux,
AIX, DU, Tru64 send a break of duration milliseconds. FreeBSD and NetBSD and HP-UX
and MacOS ignore the value of duration. Under Solaris and Unixware, tcsendbreak
with nonzero duration behaves like tcdrain.