jit@slic.cellbio.duke.edu (06/08/91)
Hi, I am trying to find out if a keyboard buffer is empty but not reading it because I don't want to get stuck if there isn't any buffered. (on ATT SVR3) Is there a 'standard' way on unix to do this ? (I am currently reading using non-canonical mode with vmin=0, then ungetc if there is any. Hopefully there is an easier way.) Thanks in advance. -- -------------------------------------------------------- Jit Keong Tan | internet: jit@slic.cellbio.duke.edu (919) 684-8098 | bitnet : tan00001@dukemc.bitnet
mycroft@kropotki.gnu.ai.mit.edu (Charles Hannum) (06/08/91)
In article <22368@duke.cs.duke.edu> jit@slic.cellbio.duke.edu writes:
Hi, I am trying to find out if a keyboard buffer is empty but not reading
it because I don't want to get stuck if there isn't any buffered.
(on ATT SVR3)
Is there a 'standard' way on unix to do this ?
You can use select(2) under BSD, or set the terminal to non-blocking I/O
(using the FIONBIO ioctl), try to read, and see if you get EWOULDBLOCK.
Details available upon request. B-)guy@auspex.auspex.com (Guy Harris) (06/10/91)
> Hi, I am trying to find out if a keyboard buffer is empty but not reading > it because I don't want to get stuck if there isn't any buffered. > (on ATT SVR3) > > Is there a 'standard' way on unix to do this ? > >You can use select(2) under BSD, Unfortunately, he's not *using* BSD; he's using System V Release 3, as he said. No, SVR3 doesn't necessarily have "select()", nor the FIONBIO "ioctl", nor EWOULDBLOCK. Answer: it does have non-blocking I/O on ttys; check out the F_GETFL and F_SETFL "fcntl" calls. WARNING: unlike various things in BSD, non-streams ttys return 0, not -1, if no data is available to be read and they're in non-blocking mode. The program must make absolutely positively sure that it doesn't leave the terminal in non-blocking mode; otherwise, if it exits and leaves the terminal in that mode, the shell may see a zero-byte return if the user doesn't type a command fast enough, will think that's an end-of-file, and exit.