In CVS boost/iostreams/filter/zlib.hpp, revision 1.21 there is: ... struct zlib_params { // Non-explicit constructor. zlib_params( int level = zlib::default_compression, int method = zlib::deflated, int window_bits = zlib::default_window_bits, int mem_level = zlib::default_mem_level, int strategy = zlib::default_strategy, bool noheader = zlib::default_noheader, bool calculate_crc = zlib::default_crc ) : level(level), method(method), window_bits(window_bits), mem_level(mem_level), strategy(strategy), noheader(noheader), calculate_crc(zlib::default_crc) { } ... g++ -Wall -W (correctly) states: .../boost/iostreams/filter/zlib.hpp:120: warning: unused parameter 'calculate_crc' Normally I wouldn't worry about trivial warnings, but in this case the argument is being ignored when initialising the member data which looks a bit odd to me... phil -- change name before "@" to "phil" for email