Re: UNIX Compressed Files From A PC

["Marin D. Condic" <mcondic-nospam@acm.org>]

Don Yuniskis wrote:
> Are you looking for files that have been compress(1)-ed, freeze(1)-d,
> zip(1)-ed, gzip(1)-ed, bzip2(1)-ed, etc.?  The algorithms used differ.
> 
I am told the files were compressed via "compress" and that it uses the
LZW compression algorithm.

> I assume you *really* mean a "package" and not some other solution
> to your problem (i.e. unpacking them outside *your* application).
> If you want to be able to *write* to the packed files, then you obviously
> either want them to be unpacked before you access them or "wrap" the
> open/close with unpack/pack...  ?
> 
Let me clarify. I want a package, as in "Ada package", that I can
compile and link to which does Open/Read/Write/Seek/Close for compressed
files. I could use a C++ class - possibly an extension of the MFC
"CFile" class - that would do the same.

I think you're confused about the "write" thing. If you are familiar
with the Win32.LZExpand package in the Win32ada bindings (or the same
stuff in the Win32api) these OS routines do *exactly* what I need - but
refuse to do anything with Unix ".z" files. They will work with files
compressed under NT just fine. The "write" of which I speak is a matter
of wanting to open a file for output, write bytes to it, close it and
have a compressed file when I'm done. I don't think it would be very
easy to do both reads and writes to a sequential file of bytes even if
it wasn't compressed and I can't imagine trying to do that with a
compressed file. :-)

> Or, was the reference to "write" an overzealous typo?  :>
> 
Nope. See above.


> The sources to all of the compressors/decompressors in popular use
> are readily available (though almost always written in C)
> 
A URL or two may come in handy. I can cope with it being written in C. I
can even cope with it being extremely badly written in C, provided I get
two things: A) The Open/Read/Write/Seek/Close functions I need where I
send it a file handle and get back a buffer full of bytes (or the other
direction) and B) It functions reliably so I don't have to debug it and
hammer on it to get it to work.

My problem in this case is time. I've got a program that is accessing
files through a bunch of standard issue Windows calls where
Open/Read/Write/Seek/Close are the functions being used. I need to make
a change to the software so it can pick up files across a network from a
Unix box where the files are compressed. I can't change the requirements
and I don't have a lot of time to get a solution in place, so I thought
if I had either an Ada package or C++ class that did the same things, I
could "leverage software reuse" by simply plugging in the new package
with maybe a little glue software around it. If you know of something
that fits this description, please let me know. Thanks.

MDC
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Marin David Condic - Quadrus Corporation - http://www.quadruscorp.com/
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