Thom DeCarlo (trdecarlo++at++tasc.com)
Wed, 23 Jun 1999 23:13:35 -0400
Don Hatch wrote:
> On Jun 23, 9:21pm, Thom DeCarlo wrote:
> > Subject: WOT: Testing stdin
> > Hi,
> > I apologize for this message being Way Off Topic, but I'm at a loss for
> > how to continue.
> >
> > The problem is, how do I test whether anything has been typed to stdin
> > without blocking the program if the input buffer is empty? Of course,
> > the simple things don't work. I've tried getc(), fgetc(), gets(),
> > scanf(), .... They all block until a '\n' is typed. I just want the test
> > to fail and continue if nothing is waiting in the buffer.
> >
> > Any ideas from you C++ gurus out there?
> >
> > TIA,
> > Thom
> >
> >
> > -----------------------------------------------------------------------
> > List Archives, FAQ, FTP: http://www.sgi.com/software/performer/
> > Submissions: info-performer++at++sgi.com
> > Admin. requests: info-performer-request++at++sgi.com
> >-- End of excerpt from Thom DeCarlo
>
> Not off topic at all! You need to know how to do this
> to get keyboard input in any Performer simulation loop.
>
> Use select() to query whether stdin (fileno = 0) has characters
> waiting to be read.
> If it says yes, then you should be able to call getc()
> or fgets() to get a line of input without it blocking.
>
> You'll have to experiment with the details of stdio buffering
> (e.g. what happens when there's more than one line of input waiting?
> I suspect the second line might get buffered and so you'll get fooled
> into thinking it's not there).
> You can probably avoid this issue by calling setbuf(stdin, NULL),
> or use read() directly instead of the buffered stdio calls.
>
> Don
>
> --
> Don Hatch hatch++at++sgi.com (650) 933-5150 Silicon Graphics, Inc.
Well, I guess I have to admit it. I'm not writing this on an SGI. I'm on WinNT
using VC++ 6.0 and VegaNT.
I can't find anything on this machine that defines the select() function. And
the read() function still blocks until '\n' is entered. I did find an
_filelength() function which I thought might work, but it just returns an
error whether anything is on the input buffer or not.
Thom
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