Sven Van Echelpoel wrote: [...]

Are you sure that that's defined for all translation units that use or implement Boost.Regex?

Yep. Double checked it now and it is defined at the project level for every project [...]

...

Searching through the sourcecode for #pragma comment( lib, ... ) and #pragma comment( linker, ... ) directives came up empty as did a search for boost_regex_vc6_mdsd.lib in all sources and headers.

It's in "boost/regex/v3/regex_library_include.hpp".

Found it. I can now see I need to define the guard macro BOOST_REGEX_NO_LIB to disable the auto-linking. Doing so makes everything build just fine. Thanks, Sven