These functions perform miscellaneous control actions on terminal
devices. As regards terminal access, they are treated like doing
output: if any of these functions is used by a background process on its
controlling terminal, normally all processes in the process group are
sent a SIGTTOU signal. The exception is if the calling process
itself is ignoring or blocking SIGTTOU signals, in which case the
operation is performed and no signal is sent. See Job Control.
— Function: int tcsendbreak (int filedes, int duration)
This function generates a break condition by transmitting a stream of
zero bits on the terminal associated with the file descriptor
filedes. The duration of the break is controlled by the
duration argument. If zero, the duration is between 0.25 and 0.5
seconds. The meaning of a nonzero value depends on the operating system.
This function does nothing if the terminal is not an asynchronous serial
data port.
The return value is normally zero. In the event of an error, a value
of -1 is returned. The following errno error conditions
are defined for this function:
EBADF
The filedes is not a valid file descriptor.
ENOTTY
The filedes is not associated with a terminal device.
— Function: int tcdrain (int filedes)
The tcdrain function waits until all queued
output to the terminal filedes has been transmitted.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time tcdrain is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to tcdrain should be
protected using cancellation handlers.
The return value is normally zero. In the event of an error, a value
of -1 is returned. The following errno error conditions
are defined for this function:
EBADF
The filedes is not a valid file descriptor.
ENOTTY
The filedes is not associated with a terminal device.
The tcflush function is used to clear the input and/or output
queues associated with the terminal file filedes. The queue
argument specifies which queue(s) to clear, and can be one of the
following values:
TCIFLUSH
Clear any input data received, but not yet read.
TCOFLUSH
Clear any output data written, but not yet transmitted.
TCIOFLUSH
Clear both queued input and output.
The return value is normally zero. In the event of an error, a value
of -1 is returned. The following errno error conditions
are defined for this function:
EBADF
The filedes is not a valid file descriptor.
ENOTTY
The filedes is not associated with a terminal device.
EINVAL
A bad value was supplied as the queue argument.
It is unfortunate that this function is named tcflush, because
the term “flush” is normally used for quite another operation—waiting
until all output is transmitted—and using it for discarding input or
output would be confusing. Unfortunately, the name tcflush comes
from POSIX and we cannot change it.
— Function: int tcflow (int filedes, int action)
The tcflow function is used to perform operations relating to
XON/XOFF flow control on the terminal file specified by filedes.
The action argument specifies what operation to perform, and can
be one of the following values:
TCOOFF
Suspend transmission of output.
TCOON
Restart transmission of output.
TCIOFF
Transmit a STOP character.
TCION
Transmit a START character.
For more information about the STOP and START characters, see Special Characters.
The return value is normally zero. In the event of an error, a value
of -1 is returned. The following errno error conditions
are defined for this function:
EBADF
The filedes is not a valid file descriptor.
ENOTTY
The filedes is not associated with a terminal device.
EINVAL
A bad value was supplied as the action argument.
Published under the terms of the GNU General Public License
