Reading "leftover" chunks from files

Reading "leftover" chunks from files

[Matthew]

Greetings,

This is a "what's the best way of doing this" question.

I want to read in a file so that I can get fixed-length chunks of data
backwards, and also read in whatever data (smaller than the chunk size)
is left behind at the end of the file.

EG
If the file I'm reading is:

[ABC|DEF|GHI|JK] (where | represents a chunk border, not an actual byte)

I want to be able to read:
JK, then
GHI, then
DEF, then
ABC

I'd say Direct_IO comes into it, and the full-sized chunks (eg ABC) are
easy to get, but how do I pick up the JK without scanning through the
whole file?

MB
Email: ua.ten.qu@olokom (backwards)
-- 
How am I supposed to hallucinate with all of these coloured lights
distracting me?

Re: Reading "leftover" chunks from files

[Matthew]

Greetings,

Ooops, wrong email address: ua.ten.qu@okolom
-- 
How am I supposed to hallucinate with all of these coloured lights
distracting me?

Re: Reading "leftover" chunks from files

[Robert Dewar]

In article <37BCD2F1.E0AECF04@Think.So>,
  Matthew <I.Dont@Think.So> wrote:
> Greetings,
>
> This is a "what's the best way of doing this" question.
>
> I want to read in a file so that I can get fixed-length chunks
of data
> backwards, and also read in whatever data (smaller than the
chunk size)
> is left behind at the end of the file.

Direct_IO and Sequential_IO are NEVER appropriate for this kind
of job, since they output data in implementation dependent form.
Always use stream_io for a task like this, and then you have
complete control over what you read, and from where you read
it in the file.


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Re: Reading "leftover" chunks from files

[tmoran]

>Direct_IO and Sequential_IO are NEVER appropriate for this kind
>of job, since they output data in implementation dependent form.
>Always use stream_io for a task like this, and then you have
>complete control over what you read, and from where you read
>it in the file.
  Don't forget that for streams "complete control" also means
"responsibility", since the default 'Read and 'Write are
implementation dependent and may or may not do what you
want or expect.

Re: Reading "leftover" chunks from files

[Jean-Pierre Rosen]

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Matthew <I.Dont@Think.So> a �crit dans le message :
37BCD2F1.E0AECF04@Think.So...
.
>
> I want to read in a file so that I can get fixed-length chunks of data
> backwards, and also read in whatever data (smaller than the chunk size)
> is left behind at the end of the file.

I have written a package called Direct_Text_IO. It is a mixture of Direct_IO
and Text_IO, i.e. it allows random access in a text file.
It provides usual operations on Character and strings, and deals properly
with end of lines and end of pages.
It is not finalized (i.e. I didn't yet write the documentation); once it is
done, I will put it on Adalog's components page.
In the mean time, send me a note if you want to try it (my ISP refuses
attachments in this newsgroup).
Feel free to use it and report any problem you may encounter !

--
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           J-P. Rosen (Rosen.Adalog@wanadoo.fr)
Visit Adalog's web site at http://perso.wanadoo.fr/adalog