[Boost-users] troubles with boost filtering streams

Subject: [Boost-users] troubles with boost filtering streams
From: Daniel Oberhoff (daniel_at_[hidden])
Date: 2011-01-23 09:24:27

Hi,

I am working on a matlab file reader/writer. Since matlab uses zip to 
compress variables I was thinking I could use the boost filtering 
streams with the zip filter to handle that. The use case is that there 
are zipped blocks inside the file, i.e. not the whole file is zipped 
but just parts. I am not sure how to handle that with boost, since I 
would need to start/stop zipping/unzipping at almost arbitrary points 
in the file.

Also I have trouble working with filtering streams at all. As a 
baseline test I started substituting the fstream I was reading from 
with a boost filtering istream onto which I pushed the fstream. Reading 
works fine for a while and then breaks. What I noted is that the 
fstream tellg always lags behind the actual number of bytes read. also 
using the fitlering streams tellg breaks the whole stream. also seeking 
does not seem to work with the filtering stream. I need to seek quite 
often. seeking only happens when not unzipping. I tried seeking on the 
fstream instead. that worked up to some point(as stated above). I fear 
the seeking on the fstream breaks the filtering stream, but seeking on 
the filtering stream doesn't work.

If anyone has pointers that would be great.

Best

Daniel