Re: [Boost-users] Read/write with gzip

Subject: Re: [Boost-users] Read/write with gzip
From: Anders Knudby (knudby_at_[hidden])
Date: 2011-04-27 14:05:47

On Wed, Apr 27, 2011 at 12:27 PM, Ted Byers <r.ted.byers_at_[hidden]> wrote:

>
>
> On Tue, Apr 26, 2011 at 8:54 PM, Anders Knudby <knudby_at_[hidden]> wrote:
>
>> Hello, I previously managed to write data to a gzipped file using the
>> following code structure (it's an example of course, the "memblock" is
>> actually filled with real data and the real filename is specified
>> elsewhere).
>>
>> #include <boost/iostreams/filtering_streambuf.hpp>
>> #include <boost/iostreams/filtering_stream.hpp>
>> #include <boost/iostreams/copy.hpp>
>> #include <boost/iostreams/filter/gzip.hpp>
>> #include <boost/iostreams/device/file_descriptor.hpp>
>> #include <boost/filesystem.hpp>
>>
>> namespace io = boost::iostreams;
>>
>> int size = 1000;
>> char* memblock = new char [size];
>>
>> io::filtering_ostream out;
>> out.push(io::gzip_compressor());
>> out.push(io::file_descriptor_sink("c:/outfile.gz"));
>> out.write (memblock, size);
>>
>>
>> Is there a reason not to invoke the stream's member function 'close' at
> this point?  You are, after all, reopening the same file later in your
> program.
>
> Cheers
>
> Ted
>
>
Thanks for the help. The problem of writing the file and then trying to read
it later in the same process is an artefact of my example, in reality I have
one program to write the files, and another to read them again. But the
reason I'm not specifically closing the filtering_stream is that I don't
know how! I thought I could treat it as a normal iostream (e.g. using read,
write etc.), but the normal closing of an iostream - in.close() - doesn't
compile. Instead it gives me the following error: "error C2039: 'close' : is
not a member of 'boost::iostreams::filtering_stream<Mode>". I have found a
mention somewhere that I need to make the filtering_stream 'closeable', but
I haven't found out how to do that. Any help would be appreciated, I do like
to close my streams...

In the meantime, I have somehow managed to get my code to work. I'm not sure
how, but it is definitely related to the closing or not of the
filtering_stream. If someone has a simple example of how to create and then
close/destroy a filtering_streambuf that would be great. I can't find a
single example in the Boost documentation, but maybe I'm just not looking in
the right place or sufficiently code-literate.

Anders