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From: krause@uiucdcsm.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Truncating MS-DOS files
Message-ID: <8000001@uiucdcsm>
Date: Wed, 18-Feb-87 18:50:00 EST
Article-I.D.: uiucdcsm.8000001
Posted: Wed Feb 18 18:50:00 1987
Date-Received: Fri, 20-Feb-87 22:36:30 EST
References: <123004@<1987Feb15>
Lines: 33
Nf-ID: #R:<1987Feb15:123004:uiucdcsm:8000001:000:1479
Nf-From: uiucdcsm.cs.uiuc.edu!krause    Feb 18 17:50:00 1987


> Well, quite some time ago I also heard that CX=0 on a write would truncate
> the file.  When I became curious about it recently, I looked in the IBM
> PC-DOS Technical reference manuals for DOS 2.1 and 3.0 (the only ones I
> had available).  I looked in the function documentation distributed to
> OEM's by Microsoft for MS-DOS 2.0.  I also looked in the book
> "Advanced MS-DOS" by Ray Duncan.
> 
> None of these sources mentioned a thing about CX=0 being a legal value or
> not, much less saying that it allows you to truncate a file.
> ...
> Perhaps you could give us some clue about WHERE you saw it stated, instead
> of simply yelling at us for being so ignorant as to overlook the
> documentation.  Thanks for your time.
> -- 
> Roy J. Mongiovi
> ...!{akgua, allegra, amd, hplabs, ihnp4, masscomp, ut-ngp}!gatech!gitpyr!roy

I checked two of the three sources mentioned and found the CX=0 behavior
documented (Advanced MS-DOS, p. 320, and IBM DOS Tech. Ref. Ver. 2.10, p. 5-28)
under function call 28H, as specified in the posting to which you are
referring.  I didn't check the DOS 3.0 manual because I don't have one.

Perhaps you could give us some clue about WHERE you looked?? :-)

What I would like to know is, does this work with the handle file calls?
(i.e. function call 40H, Write to file or device, after a lseek)

				James Krause
				krause@uicsrd.CSRD.UIUC.EDU

P.S.  It took me a while to realize what "RTFM" meant and then I, too,
	was offended a bit....