C++ String Wrapper Classes

First should understand that Windows APIs are defined and documented in terms of TCHAR,which can be MBCS or Unicode characters depending on whether you define the _MBCS or _UNICODE symbol when compiling.

Type:                                Meaning:
WCHAR                         Unicode character(wchar_t)
TCHAR                          MBCS or Unicode character, depending on preprocessor settings
LPSTR                            string of char(char *)
LPCSTR                         constant string of char(const char *)
LPWSTR                        string of WCHAR(WCHAR *)
LPCWSTR                     constant string of WCHAR(const WCHAR *)
LPTSTR                         string of TCHAR(TCHAR *)
LPCTSTR                      constant string of TCHAR(const TCHAR *)
OLECHAR                    Unicode character(wchar_t)
LPOLESTR                  string of OLECHAR(OLECHAR *)
LPCOLESTR                constant string of OLECHAR(const OLECHAR *)
_T(x)                             Prepends L to the literal in Unicode builds

Also there are also some variants on _T that you might encouter in documentation or sample code, there are TEXT,_TEXT,__TEXT,and __T,that all do the same things

MFC Classes:
An MFC CString holds TCHARs,so the exact character type depends on the preprocessor symbols you have defined. In general, CString is like a STL string .
Following some examples:
CString s1=”char string”;//construct from a LPCSTR
CString s2=_T(”wide char string”);//construct from a LPCWSTR

NOTE: The only legal cast you can apply to a CString is a cast to LPCTSTR, you should know that cast to LPTSTR is wrong.If you want to cast to LPTCHAR, please use CString.GetBuffer(0),but you should invoke the CString.ReleaseBuffer after you use that.