Well there's something wrong at your end, because it works for me:

cd libs/regex/example/grep g++ -I../../../.. -c -o grep.o grep.cpp g++ -o grep.exe grep.o 'C:\data\boost\develop\boost\bin\boost\libs\regex\build\libboost_regex.lib\mingw\debug\threading-multi\libboost_regex-mgw-mt-d-1_33.lib' 'C:\data\boost\develop\boost\bin\boost\libs\program_options\build\libboost_program_options.lib\mingw\debug\threading-multi\libboost_program_options-mgw-mt-d-1_33.lib' -g3

compiles and links cleanly with the current MinGW release.

John.

Thanks John, for your time and quick answers. I found the issue: I compiled "grep.cpp" with -O3 and this leads to: - error at linking on debug version of the library (libboost_regex-mgw-mt-d-1_33.lib) - OK linking with non-debug version (libboost_regex-mgw-mt-1_33.lib) I am quite unfamiliar with g++ (and it is quite off topic here) but seems strange to me that an optimization level ruins a linking... Arno