[boost] [iostreams][gzip][zlib] zlib vs gzip, and linking against external libraries

What is the difference in functionality between gzip and zlib compression? I built Boost iostreams library on Linux after exporting ZLIB_SOURCE and BZIP2_SOURCE environment variables. However when I build a sample program using gzip / bzip2 with IOStreams, I do not need to link to libzlib or libbz2. Is the zlib / bz2 code built into libboost_iostreams in this case? For reference, this is the command line I used to build the iostreams library. ./b2 --with-iostreams --build-dir=../build threading=multi variant=release link=shared runtime-link=shared -- Aaron Levy aaron.levy@yandex.com