nather@utastro.UUCP (Ed Nather) (08/13/84)
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In moving small C programs between an IBM PC and a Vax running 4.2bsd Unix,
I have been struck by the very different way in which console I/O must be
handled. These programs are interactive and expect single-character
commands (not echoed) from the keyboard.
Under 4.2bsd Unix I must put the tty driver into "cbreak" mode, or "raw"
mode if I want no input processing at all, then find out if the user has
typed anything, interpret it, and respond. If I want to return to "normal"
console I/O I must discuss the matter with the tty driver again.
Using DeSmet C (an example -- other compilers for the PC have equivalent
features) I can switch between processed character input (getc() or
getchar()) and raw input by simply using a different character call;
in DeSmet C the function ci() gets an unprocessed, unechoed character
from the keyboard, co() writes one on the console screen. I can go back
and forth between processed or unprocessed i/o very simply. There is also
a function that tells you if a character has been typed, without waiting
for one -- *very* useful in many programs to check for "pseudo-interrupts"
during a lengthy procedure, or to provide console feedback about what the
program is doing.
I suspect these extra, "non-standard" funtion calls violate some general
religious principle about treating all devices alike, but they are *very*
useful, and I would trade Purity any day to have them available on the
Vax Unix system.
Comments?
--
Ed Nather
{allegra,ihnp4}!{ut-sally,noao}!utastro!nather
Astronomy Dept., U. of Texas, Austinjpm@bnl.ARPA (09/10/84)
> To do unbuffered I/O on Unix systems without playing with the tty driver >you can use the lowest level I/O commands (short of asm), read and write. But that wont get the same thing as turning CBREAK on. The read() call still wont return until a full line has been typed. There is no call in Unix like ci() in DeSmet C. ci() can be simulated by going into CBREAK mode, reading one character, and then going back to normal. A better idea might be to rework the program to use CBREAK mode at all times. -- John McNamee ..!decvax!philabs!sbcs!bnl!jpm jpm@Bnl.Arpa "Use a modem, Go to jail"