Wide character support is currently detected by libstdcpp3.hpp.
Is that detection not working?
I guess not. The filesystem library failed to build on cygwin with wchar-ish errors until I installed gcc4.
I've just investigated this and: * Boost.Config is defining the correct wide-character defect macros for both gcc-3 and gcc-4 on cygwin. * Boost.Filesystem either isn't making use of them at all (the v3 code) or has outdated workarounds (v2). I'm attaching a patch for the filesystem v2 code, but the v3 code Beman will have to fix if this is to work on non-wide-character platforms. BTW gcc 3 & 4 seem to co-exist quite happily on current cygwin, but as the default is still gcc-3 I guess we should still try and support non-wide-character platforms? HTH, John.