Advanced Programming in the UNIX® Environment

ptg10805159

708 Te rminal I/O Chapter 18

void

tty_atexit(void) /* can be set up by atexit(tty_atexit) */

{

if (ttysavefd >= 0)

tty_reset(ttysavefd);

}

struct termios *

tty_termios(void) /* let caller see original tty state */

{

return(&save_termios);

}

Figure 18.20Set terminal mode to cbreak or raw

Our definition of cbreak mode is the following:

•Noncanonical mode. As we mentioned at the beginning of this section, this

mode turns offsome input character processing. It does not turn offsignal

handling, so the user can always type one of the characters that triggers a

terminal-generated signal. Be awarethat the caller should catch these signals;

otherwise, there’s a chance that the signal will terminate the program, and the

terminal will be left in cbreak mode.

As a general rule, whenever we write a program that changes the terminal

mode, we should catch most signals. This allows us to reset the terminal mode

beforeterminating.

•Echo off.

•One byte at a time input.To dothis, we set MIN to 1 and TIME to 0. This is case

BfromFigure18.19. Areadwon’t return until at least one byte is available.

We define raw mode as follows:

•Noncanonical mode. We also turn offprocessing of the signal-generating

characters (ISIG)and the extended input character processing (IEXTEN).

Additionally, we disable a BREAK character from generating a signal, by turning

offBRKINT.

•Echo off.

•Wedisable the CR-to-NL mapping on input (ICRNL), input parity detection

(INPCK), the stripping of the eighth bit on input (ISTRIP), and output flow

control (IXON).

•Eight-bit characters (CS8), and parity checking is disabled (PARENB).

•All output processing is disabled (OPOST).

•One byte at a time input (MIN = 1, TIME = 0).

The program in Figure18.21 tests raw and cbreak modes.