Advanced Programming in the UNIX® Environment

ptg10805159

710 Te rminal I/O Chapter 18

Running the program in Figure18.21, we can see what happens with these two

terminal modes:

$./a.out

Enter raw mode characters, terminate with DELETE

4

33

133

61

70

176

type DELETE

Enter cbreak mode characters, terminate with SIGINT

1 type Control-A

10 type backspace

signal caught type interrupt key

In raw mode, the characters entered wereControl-D( 04 )and the special function key

F7. On the terminal being used, this function key generated five characters:ESC( 033 ),[

( 0133 ), 1 ( 061 ), 8 ( 070 ),and ̃( 0176 ).Note that with the output processing turned offin

raw mode ( ̃OPOST), we do not get a carriage return output after each character.Also

note that special-character processing is disabled in cbreak mode (so, for example,

Control-D, the end-of-file character,and backspace aren’t handled specially), whereas

the terminal-generated signals arestill processed.

18.12 Terminal WindowSiz e

Most UNIX systems provide a way to keep track of the current terminal window size

and to have the kernel notify the foreground process group when the size changes. The

kernel maintains awinsizestructurefor every terminal and pseudo terminal:

struct winsize {

unsigned short ws_row; /* rows, in characters */

unsigned short ws_col; /* columns, in characters */

unsigned short ws_xpixel; /* horizontal size, pixels (unused) */

unsigned short ws_ypixel; /* vertical size, pixels (unused) */

};

The rules for this structureare asfollows:

•Wecan fetch the current value of this structureusing anioctl(Section 3.15) of

TIOCGWINSZ.

•Wecan storeanew value of this structure in the kernel using anioctlof

TIOCSWINSZ.Ifthis new value differs from the current value stored in the

kernel, aSIGWINCHsignal is sent to the foreground process group. (Note from

Figure10.1 that the default action for this signal is to be ignored.)