eg wrote:

Milan Svoboda wrote:

...

Hi All,

I'm using boost::iostreams and its filters to compress and decompress data. However I'm not able to retrieve number of bytes really written (number of bytes after a compression).

Does anybody know how to do that?

I'm currently using following code:

coffset if offset to where start with writing of compressed data and after call it shall contain the length of the file. This works good to get length of the compressed block unless block of data is written somewhere in the middle of the file thus end of file is not the same as the last offset where compressed data has been written to.

io::file_descriptor file(fd); file.seek(coffset, ios_base::beg); { io::filtering_ostream out; // Push the compression filter (bl->type.push(out);) out.push(file);

io::write(out, buf, length);

// Destroying the object 'out' causes all filters to // flush. } // Update raw length of the file. // coffset = file.seek(0, ios_base::end);

Maybe I dont quite understand the problem...

I need to know number of bytes after compression. boost::iostreams::write returns number of bytes that has been passed to filter but there is no direct way to get number of bytes that filter returned...

Could you just write a simple pass-through filter which counts the bytes only? Something like:

io::filtering_ostream out; out.push(compressor()); out.push(passthru()); // <- this just counts bytes out.push(file_sink("my_file.txt"));

Great! This looks like a right way. Thank you! Milan