Re: OT: Checking if any chars available on stdin under Windows

Well, if eof(0) returns -1, it means there was an error with file descriptor 0 (stdin) indicating that the stdin is not open. This tells us whether the program is being piped to or not. This is a simple non-blocking way to determine if the program can read from stdin or not.

You can verify this in MSVC help :)

Mark Webster

On Fri, Apr 23, 2004 at 04:33:38PM -0400, tweety wrote:
> Just a shot in the dark here, but on windows wouldn't eof return true only
> then it encounters ^Z? 
> 
> ----------------------------------
> Peace and love,
> Tweety
> [email protected] - [email protected]
> YahooID: tweety_04_01
> 
> 
> 
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Mark
> Webster
> Sent: April 23, 2004 11:26 AM
> To: [email protected]
> Subject: Re: [GD-General] OT: Checking if any chars available on stdin under
> Windows
> 
> Ok, the solution appears to be to check _eof(0); - If it returns -1, there's
> nothing on stdin.
> 
> I *think* that's the answer you're looking for.
> 
> Mark Webster
> 
> > ----- Original Message ----- 
> > From: "Colin Fahey" <[email protected]>
> > To: <[email protected]>
> > Sent: Friday, April 23, 2004 3:31 PM
> > Subject: [GD-General] OT: Checking if any chars available on stdin under
> > Windows
> >
> >
> > >
> > > 2004 April 22nd
> > > Friday
> > >
> > > Off-Topic question here...but I just spent an hour doing Google
> > > searching and reading other online documentation, and I'm not
> > > finding any answers to the following:
> > >
> > > QUESTION:  How can I check if stdin (standard input) has any
> > > characters available for reading under WINDOWS (not Linux)?
> > >
> > > I thought (cin.rdbuf()->in_avail()) would be the cool hacked
> > > solution -- but even after doing Sleep(1000), cin.sync_with_stdio(),
> > > and wackier and wackier things to try to make "cin" up-to-date,
> > > so to speak, the expression above ALWAYS yields zero, whether or
> > > not there are characters available on the input stream.
> > > (Compiled using Visual C++ 6.0 under Windows 2000)
> > >
> > > If I have a command line like the following:
> > >
> > >         testapp
> > >
> > > then the following code blocks indefinitely:
> > >
> > >         int c = cin.peek();
> > >
> > > but if the command line is as follows:
> > >
> > >         more textfile.txt | testapp
> > >
> > > then the application does not block.  But in both
> > > cases (cin.rdbuf()->in_avail()) is zero.
> > >
> > > How can "testapp" in the two command line examples
> > > above DETECT which scenario (piped input or not) is
> > > involved?  That, I guess, is my real goal.  I want to
> > > know if the command line lacks the piping from
> > > another app, since this means I shouldn't wait
> > > forever for stdin data.
> > >
> > > I'd be willing to use a Win32 function to solve this
> > > problem, but if it is really tricky, like creating a
> > > thread, or something nutty, then it's probably not
> > > worth it.  Bleah, under Linux one can actually use
> > > fnctl() to change stdin to non-blocking mode (but,
> > > I assume, still buffered), which makes this problem
> > > go away -- but no fnctl() under Windows.
> > >
> > > Anyhow, probably avoiding piping data through stdin
> > > is the REAL solution to all of this mess, but that
> > > decision is not mine to make.
> > >
> > > --- Colin
> > >
> > >
> > >
> > >
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> 
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