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From: lai@math.sdsu.edu (Henry Lai )
Newsgroups: comp.os.msdos.programmer
Subject: Re: How to detect redirection?
Summary: use isatty()
Message-ID: <1990Aug8.012021.19429@ucselx.sdsu.edu>
Date: 8 Aug 90 01:20:21 GMT
References: <1426@wet.UUCP>
Sender: news@ucselx.sdsu.edu (News Admin)
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Organization: San Diego State University, Mathematical Sciences
Lines: 20

In article <1426@wet.UUCP> naga@wet.UUCP (Peter Davidson) writes:
> Let's say X.EXE is a program written in (Microsoft) C which
> calls printf() to output to the monitor.  Invoking X using
> X > PRN (or some file) redirects output to the printer (or file).
> Suppose that X does something (such as writing directly to video RAM)
> which it would not like to do if output has been redirected as above?
> How can it tell?  One solution is: Use printf() to output a charactr
> and then peek in the video RAM to see if the character went there
> (if so, no redirection).  The disadvantage is that, if redirection
> is in effect, a character (perhaps only a space) is sent to the
> printer (or file).  Is there a more elegant way to tell whether
> output has been redirected? 

	isatty (fileno (stdout))
will return zero if stdout has been redirected to a file. See the
reference to isatty in your run-time library reference.
--
Henry Lai
Internet: lai@math.sdsu.edu
    UUCP: {mcgill-vision,sobeco,uunet}!batcave!lai