ASCCharTString represents the STL parent's string class of ASCString.
If the preprocessor definition _UNICODE is defined, ASCCharTString is an STL's std::wstring to use wchar_t type.
If _UNICODE is not defined, ASCCharTString is an STL's std::string to use char type.
That way, ASCCharTString will addapt itself to the right character type needed for its internal string representation depending on the _UNICODE preprocessor definition.