[Boost-users] [filesystem] how to get wstring value from wpath::external_file_string() with gcc?

I want wpath::external_file_string to return a unicode wstring. On windows, with my visual studio project settings set to "Unicode character set", it correctly returns a wstring. But on OSX (using xcode/gcc) it tries to return a string. I believe this is due to Traits::external_string_type. This is supposed to be OS specific string type and I want my application to use Unicode for all interactions with OS (filesystem paths, command-line parameters etc), then boost will also set this type to wstring. How do I configure my project such that this trait is set to wstring? Any xcode settings or gcc parameters or #defines? SG