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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.
Preliminary: | MT-Unsafe race:tcattr(filedes)/bsd | AS-Unsafe | AC-Unsafe corrupt/bsd | See POSIX Safety Concepts.
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:
EBADFThe filedes is not a valid file descriptor.
ENOTTYThe filedes is not associated with a terminal device.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
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:
EBADFThe filedes is not a valid file descriptor.
ENOTTYThe filedes is not associated with a terminal device.
EINTRThe operation was interrupted by delivery of a signal. See Primitives Interrupted by Signals.
Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
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:
EBADFThe filedes is not a valid file descriptor.
ENOTTYThe filedes is not associated with a terminal device.
EINVALA 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.
Preliminary: | MT-Unsafe race:tcattr(filedes)/bsd | AS-Unsafe | AC-Safe | See POSIX Safety Concepts.
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:
EBADFThe filedes is not a valid file descriptor.
ENOTTYThe filedes is not associated with a terminal device.
EINVALA bad value was supplied as the action argument.
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