[Boost-users] date_time: from local time to UTC

I am using Boost 1.31 data time library with MSVC6. I want to use local TZ setting to transfer a local time to utc time. I noticed that we can use boost::date_time::c_local_adjustor<ptime>::utc_to_local() to change a utc time to local time based on local TZ settings. But this class does not have local_to_utc(). While boost::date_time::local_adjustor<ptime, -5, us_dst>::local_to_utc() works, it does not use local TZ settings. Is there anyway I can use local TZ setting to do the translation? Thanks