Re: Shortening an IFS file

[MichaelQuigley@xxxxxxxxxx]

Tim,

Thanks. ftruncate is what I was looking for. I didn't find it by my 
obviously lame search of the Infoma... uh, Knowledge center. (It's right 
there under the category of IFS APIs. Searching for truncate or even trunc 
finds it.) 

Thanks again,
Michael



From:   Tim Bronski <tim.bronski@xxxxxxxxx>
To:     Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Date:   03/12/2015 12:07 PM
Subject:        Re: Shortening an IFS file
Sent by:        "MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxx>



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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