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From: jap@convex.cl.msu.edu (Joe Porkka)
Newsgroups: comp.lang.c
Subject: Re: How do you truncate a file?
Message-ID: <1991May13.145521.8370@msuinfo.cl.msu.edu>
Date: 13 May 91 14:55:21 GMT
References: <1991May6.194614.9641@pensoft.uucp> <792@uswnvg.UUCP> <1991May9.130725.1@dev8j.mdcbbs.com> <1991May12.155309.7279@rushpc>
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jjr@rushpc (John J. Rushford Jr) writes:

>In article <1991May9.130725.1@dev8j.mdcbbs.com> campbell@dev8j.mdcbbs.com (Tim Campbell) writes:
>>In article <792@uswnvg.UUCP>, dfpedro@uswnvg.UUCP (Donn Pedro) writes:
>>> In article <1991May6.194614.9641@pensoft.uucp>, lwb@pensoft.uucp (Lance Bledsoe) writes:
>>IF you have DOS and want this to run real fast on any file of any size and
>>want it to truncate the file in place (not making a copy), then you could
>>
>>I just don't know unix well enough to know a clever way to handle this 
>>situation without actually copying the file.
>>

>In Unix the above method would wreak havoc with the filesystem if you
>could use it.  You would have to update the freelist and inode entry
>in the superblock or run fsck -y to fix the filesystem.  This would
>prove to be difficult unless you're 'root'.

It would not be a problem on UNIX, or any REAL os ( !msdos). Simply
call "ftruncate()" and let the filesystem do its business.