Vladimir, please read my answer below.
extern BOOST_PROGRAM_OPTIONS_DECL __declspec(selectany) std::string arg("arg");
So, what is the *reason* for the original linker error?
To be honest I don't know what is the reason, but it sounds like a BUG in VC7.1 linker to me. If I use default alignment in the described scenario I can link, asap I switch to 4 byte struct member alignment (boost libs are recompiled with that setting as well) linker can't find the symbol. The signature of the exported symbol is exact with the signature of looked up symbol. May be the linker makes the look-up in Lib A and Lib B only, instead of in program_options.lib. If I move the initialiazation to the header with the __declspec(selectany) decl-specifier the string is indeed present in Lib A, Lib B and program_options.lib and the linker picks one of them. Many thanks for your help. Ovanes