Both functions take a pointer to a termios structure and either return the current terminal attributes or set the terminal's attributes. Since these two functions operate only on terminal devices, errno is set to ENOTTY and 1 is returned if
filedes does not refer to a terminal device.
The argument
opt for tcsetattr lets us specify when we want the new terminal attributes to take effect. This argument is specified as one of the following constants.
TCSANOW | The change occurs immediately. |
TCSADRAIN | The change occurs after all output has been transmitted. This option should be used if we are changing the output parameters. |
TCSAFLUSH | The change occurs after all output has been transmitted. Furthermore, when the change takes place, all input data that has not been read is discarded (flushed). |
The return status of tcsetattr confuses the programming. This function returns OK if it was able to perform
any of the requested actions, even if it couldn't perform all the requested actions. If the function returns OK, it is our responsibility to see whether all the requested actions were performed. This means that after we call tcsetattr to set the desired attributes, we need to call tcgetattr and compare the actual terminal's attributes to the desired attributes to detect any differences.