Date: Wed, 21 Jul 1999 10:59:20 +0300 (IDT)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: Alain Magloire <alainm AT rcsm DOT ece DOT mcgill DOT ca>
cc: djgpp-workers AT delorie DOT com
Subject: Re: ftruncate
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On Tue, 20 Jul 1999, Alain Magloire wrote:

> I'm not sure I follow, so you are saying if I want to shrink a file, 
> I can do that by lseek()ing back and write() 0 byte ?

Yes.  But it's not a 0 byte, it's zero bytes.  That is, you tell DOS
to write zero bytes to the file.  Instead of interpreting this as a
no-op, DOS shrinks the file's size to the current file pointer
position.  Amazingly enough, it's not a bug, it's a feature ;-).

> To do this on Un*x I got to use ftruncate();

I know.  But DOS doesn't have a special system call for that, so DJGPP
uses the seek/write-zero way to emulate it.  (Now it also seeks back
before returning.)