Is there some magic required to obtain a "zlib sync flush" when using boost::iostreams::zlib_compressor ? Just invoking flush on the filter, or strict_sync on a filtering_ostream containing it doesn't see to do the job (ie I want the compressor to flush enough that the decompressor can recover all the bytes consumed by the compressor so far, without closing the stream; I remember using such a feature when driving zlib directly in the past, and there's a page http://www.bolet.org/~pornin/deflate-flush.html describing it nicely). Looking at the header, there seem to be some "flush codes" defined (notably a sync_flush) but it's unclear to me how they should be used (bearing in mind my compressor is just added into a filtering_ostream's chain, although I do have a reference to it if some specific method needs invoking). Thanks for any tips. Tim