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From: mlandau@Diamond.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Truncating MS-DOS files
Message-ID: <4141@diamond.Diamond.BBN.COM>
Date: Mon, 16-Feb-87 00:50:57 EST
Article-I.D.: diamond.4141
Posted: Mon Feb 16 00:50:57 1987
Date-Received: Mon, 16-Feb-87 19:53:28 EST
References: <1987Feb15.123004.21019@gpu.utcs.toronto.edu>
Reply-To: mlandau@Diamond.BBN.COM (Matt Landau)
Organization: BBN Laboratories, Inc., Cambridge, MA
Lines: 20
Summary: write zero bytes and close the file

In comp.sys.ibm.pc (<1987Feb15.123004.21019@gpu.utcs.toronto.edu>), 
lewan@gpu.utcs.toronto.edu (S. Lewandowsky) writes:
>
>How can I truncate a file using DOS?  

Once upon a time about a year ago, I spent several days with a debugger
tracing what I thought was an errant program which seemed to shorten its own
data files inexplicably.  In so doing, I discovered an interesting thing:

If you seek to a file position, write zero bytes, and close the file, the
file is truncated at the seek position.  This behavior is consistent in all
versions of PC- and MS-DOS from 2.0 to 3.2, but since it is not documented,
there's no guarantee it won't go away sometime in the future.

Does make it easy to implement truncate() and ftruncate() for the PC,
though.
-- 
 Matt Landau      	 		BBN Laboratories, Inc.
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