Linking mongocxx and bsoncxx static libs to another c++ project

@Danilo_Cavalcante It is not possible to build some artifacts with -fPIC and others without and then link them all together into the same binary or library. If you are building a shared library with -fPIC, then everything going into that library also needs to be built with -fPIC.

Also, why do you use target_link_libraries and target_include_directories rather than find_package?