— Function: int tcgetattr (int filedes, struct termios *termios-p)
This function is used to examine the attributes of the terminal
device with file descriptor filedes. The attributes are returned
in the structure that termios-p points to.
If successful, tcgetattr returns 0. A return value of -1
indicates an error. The following errno error conditions are
defined for this function:
EBADF
The filedes argument is not a valid file descriptor.
ENOTTY
The filedes is not associated with a terminal.
— Function: int tcsetattr (int filedes, int when, const struct termios *termios-p)
This function sets the attributes of the terminal device with file
descriptor filedes. The new attributes are taken from the
structure that termios-p points to.
The when argument specifies how to deal with input and output
already queued. It can be one of the following values:
TCSANOW
Make the change immediately.
TCSADRAIN
Make the change after waiting until all queued output has been written.
You should usually use this option when changing parameters that affect
output.
TCSAFLUSH
This is like TCSADRAIN, but also discards any queued input.
TCSASOFT
This is a flag bit that you can add to any of the above alternatives.
Its meaning is to inhibit alteration of the state of the terminal
hardware. It is a BSD extension; it is only supported on BSD systems
and the GNU system.
Using TCSASOFT is exactly the same as setting the CIGNORE
bit in the c_cflag member of the structure termios-p points
to. See Control Modes, for a description of CIGNORE.
If this function is called from a background process on its controlling
terminal, normally all processes in the process group are sent a
SIGTTOU signal, in the same way as if the process were trying to
write to the terminal. 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.
If successful, tcsetattr returns 0. A return value of
-1 indicates an error. The following errno error
conditions are defined for this function:
EBADF
The filedes argument is not a valid file descriptor.
ENOTTY
The filedes is not associated with a terminal.
EINVAL
Either the value of the when argument is not valid, or there is
something wrong with the data in the termios-p argument.
Although tcgetattr and tcsetattr specify the terminal
device with a file descriptor, the attributes are those of the terminal
device itself and not of the file descriptor. This means that the
effects of changing terminal attributes are persistent; if another
process opens the terminal file later on, it will see the changed
attributes even though it doesn't have anything to do with the open file
descriptor you originally specified in changing the attributes.
Similarly, if a single process has multiple or duplicated file
descriptors for the same terminal device, changing the terminal
attributes affects input and output to all of these file
descriptors. This means, for example, that you can't open one file
descriptor or stream to read from a terminal in the normal
line-buffered, echoed mode; and simultaneously have another file
descriptor for the same terminal that you use to read from it in
single-character, non-echoed mode. Instead, you have to explicitly
switch the terminal back and forth between the two modes.
Published under the terms of the GNU General Public License
