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From: dougs@videovax.tv.tek.com (Doug Stevens)
Newsgroups: comp.lang.c
Subject: Re: How do I SHORTEN a file without rewriting it?
Summary: Use chsize() or write 0 bytes.
Keywords: truncation
Message-ID: <6126@videovax.tv.tek.com>
Date: 5 Nov 90 17:52:16 GMT
References: <1162@bilver.UUCP> <747@csource.oz.au> <9505@jarthur.Claremont.EDU>
Organization: Tektronix TV Measurement Systems, Beaverton OR
Lines: 16

> In <1162@bilver.UUCP> alex@bilver.UUCP (Alex Matulich) writes:
> 	Is there a way to shorten a file ... ?

Turbo-C does indeed include chsize() in the library. Examining their
implementation, they use exactly the same trick, ie, a seek to the desired
point of truncation, and then a write of 0 bytes.

Look at page 1308 of the MS-DOS Encyclopedia (under Interrupt 21H, Function
40H, 'Write File or Device'):

	'If CX=0, the file is truncated or extended to the current 
	file pointer location'.

(CX is the number of bytes to write).