Re: Shortening an IFS file

[Tim Bronski <tim.bronski@xxxxxxxxx>]

If you open the file with O_TRUNC then the data will be cleared and the 
size will be set to 0.
If you want to read in the data, change it and write back a different 
size then open the file for O_RDWR, read your data, write your new data 
back where you want it and then use ftruncate(fd, newsize); with the new 
length and then close. Is that what you're looking to do?

Tim

On 3/12/2015 4:19 PM, MichaelQuigley@xxxxxxxxxx wrote:
> So do you open the file without o_Trunc, read the data in, close the file,
> open it with o_Trunc, process the data already read, and write the
> modified data back out? When the file is opened with o_Trunc, it wipes out
> the existing data before it can be read. (Unless I've done something wrong
> or simply don't understand.)
>
> "MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxx> wrote on 03/12/2015
> 10:14:08 AM:
>
> > From: Tim Brown <tim.bronski@xxxxxxxxx>
> > To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
> > Date: 03/12/2015 10:14 AM
> > Subject: Re: Shortening an IFS file
> > Sent by: "MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxx>
> >
> > I might have read your email too quickly. If you want to clear the
> contents
> > of a file before writing back to it then use the open option i
> suggested.
> > If you want to keep the contents up to a particular size then use
> ftruncate.
> > On Mar 12, 2015 2:40 PM, "Tim Bronski" <tim.bronski@xxxxxxxxx> wrote:
> >
> > > If you're using open() then you should have O_TRUNC or'ed as a flag.
> > >
> > > On 3/12/2015 2:32 PM, MichaelQuigley@xxxxxxxxxx wrote:
> > >
> > > > I'm writing a utility to remove some filler data from an IFS file.
> I'm
> > > > using the  The utility works great except that when I write the data
> back
> > > > to the IFS, there is original data past where I want the new EOF to
> be. I
> > > > can't for the life of me figure out how to shorten the file and set a
> new
> > > > (shorter) end of file.
> > > >
> > > > Any help would be greatly appreciated.
> > > >
> > > > Thanks,
> > > > Michael Quigley
> > > > Computer Services
> > > > The Way International
> > > > www.TheWay.org
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