How do I convert from LPCTSTR to std::string?

in one line:

std::string s = CT2A( lpctstr );

From your comment: "The function I am calling will take the std::string and use it as the filename when calling std::fstream::open()"

Well, that's wrong. The function really should take a tstring (defined as typedef std::basic_string<TCHAR> tstring). There are many Windows files whose name cannot be represented without Unicode. For instance, all files under \User\<myusername\My Documents\ if <myUserName> contains a non-ANSI character (and you really don't want to tell your user that he has a bad name!)

But once you've changed to tstring, it just works. You still get the same std::fstream object.