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From: bob@cald80.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Need help with MS-DOS 3.1 and COM1 device
Message-ID: <784@cald80.UUCP>
Date: Thu, 5-Feb-87 12:38:49 EST
Article-I.D.: cald80.784
Posted: Thu Feb  5 12:38:49 1987
Date-Received: Sun, 8-Feb-87 05:56:17 EST
References: <3281@hplabs.hplabs.UUCP>
Reply-To: bob@cald80.UUCP (bob)
Organization: Calspan Advanced Technology Center
Lines: 34

In article <3281@hplabs.hplabs.UUCP> drichard@hplabs.UUCP (Dave Richards) writes:
>
>I have written a DVI to HP LaserJet+ Driver that runs under both Unix
>and MS/PC-DOS.  Unfortunately, I have discovered a problem either in the
>Aztec C Run-time support, (which they deny), or a problem with MS-DOS,
>(a misunderstanding, no doubt).  I am running MS-DOS V3.1 and am
>putc()ing characters to a stream that was successfully opened via
>fopen() for "w" access to "COM1".  I check the returned pointer for NULL
>and guaranteed fopen()s success.  However, after writing BUFSIZ
>characters, putc() returns EOF.
>
>...much deleted for Pnews
>	Dave Richards at Hewlett-Packard Labs (drichard@hplabs)

I have found that fopen()ing a file causes the system to assume that
you are going to send text to it.  It usually turns on ^Z mapping to
end of file.  It also does \n to \r\n mapping.  Needless to say, you
can't pump binary to it.

In the Desmet C compiler, there is a different call for opening the
file for binary out.  I have found that instead of fopen() one should
use open() when using write() to stuff things out to a file.  This
probably goes back to my experience in programming on UNIX.  Files
opened with fopen() are streams which one usually sends output to with
things like fprintf and putc. And open is for unbuffered read()s and
write()s.

Try to use open() on COM1 and see if that has any better success.

-- 
					Bob Meyer
					Calspan ATC
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