---
name: "tcsendbreak"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/tcsendbreak"
---

# tcsendbreak(3)

line control functions

## NAME

**tcdrain**, **tcflow**, **tcflush**, **tcsendbreak** – line control functions

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<termios.h\>**

*int*\

**tcdrain**(*int fildes*);

*int*\

**tcflow**(*int fildes*, *int action*);

*int*\

**tcflush**(*int fildes*, *int action*);

*int*\

**tcsendbreak**(*int fildes*, *int duration*);

## DESCRIPTION

The **tcdrain**() function waits until all output written to the terminal referenced by *fildes* has been transmitted to the terminal.

The **tcflow**() function suspends transmission of data to, or the reception of data from, the terminal referenced by *fildes*, depending on the value of *action*. The value of *action* must be one of the following:

- *TCOOFF*

  Suspend output.

- *TCOON*

  Restart suspended output.

- *TCIOFF*

  Transmit a STOP character, which is intended to cause the terminal to stop transmitting data to the system. (See the description of IXOFF in the ‘Input Modes’ section of [termios(4)](/termios/4.md)).

- *TCION*

  Transmit a START character, which is intended to cause the terminal to start transmitting data to the system. (See the description of IXOFF in the ‘Input Modes’ section of [termios(4)](/termios/4.md)).

The **tcflush**() function discards any data written to the terminal referenced by *fildes* which has not been transmitted to the terminal, or any data received from the terminal but not yet read, depending on the value of *action*. The value of *action* must be one of the following:

- *TCIFLUSH*

  Flush data received but not read.

- *TCOFLUSH*

  Flush data written but not transmitted.

- *TCIOFLUSH*

  Flush both data received but not read and data written but not transmitted.

The **tcsendbreak**() function transmits a continuous stream of zero-valued bits for four-tenths of a second to the terminal referenced by *fildes*. The *duration* parameter is ignored in this implementation.

## RETURN VALUES

Upon successful completion, all of these functions return a value of zero.

## ERRORS

If any error occurs, a value of -1 is returned and the global variable *errno* is set to indicate the error, as follows:

- \[EBADF\]

  The *fildes* argument is not a valid file descriptor.

- \[EINTR\]

  A signal interrupted the **tcdrain**() function.

- \[EINVAL\]

  The *action* argument is not a proper value.

- \[ENOTTY\]

  The file associated with *fildes* is not a terminal.

## SEE ALSO

[tcsetattr(3)](/tcsetattr/3.md), [termios(4)](/termios/4.md)

## STANDARDS

The **tcsendbreak**(), **tcdrain**(), **tcflush**() and **tcflow**() functions are expected to be compliant with the IEEE Std 1003.1-1988 (“POSIX.1”) specification.