Strings come in a number of different character sets. COM components often need to use multiple character sets and occasionally need to convert from one set to another. ATL provides a number of string conversion classes that convert from one character set to another, if necessary, and do nothing when they are not needed.
CComBSTR class is a smart string class. This class properly allocates, copies, and frees a string according to the
BSTR string semantics.
CComBSTR instances can be used in most, but not all, of the places you would use a
CString class is a new addition to ATL, with roots in MFC. This class handles allocation, copying, formatting, and offers a host of advanced string-processing features. ...