Are MFC CString and LPTSTR interchangeable?

Question

I am trying to use a DLL with an ANSI C compiler. One of the DLL functions takes a void pointer. In some sample Windows code that was provided with the DLL, the struct that gets passed to the function is defined as having three CString entities. I have told the author of the DLL that they should not be passing MFC classes through their DLL functions. They have told me just to replace the CString declarations in the struct with char arrays and it should be fine. I'm 99% sure that's wrong, but since I don't have VC++ and don't have any experience with MFC, and since I've seen some posts saying LPTSTR can be used in place of CString ( What is `CString`? ), I'm starting to wonder if I'm wrong.

Can someone please confirm for me that CString and LPTSTR are not interchangeable as arguments to a function? If you can provide the source for the definition of the CString class, that would be helpful so I can send it to the DLL's author and explain that the memory footprint of a char array is not the same as a CString class, and that you can't pass a pointer to a struct that was defined with char arrays and then treat it as a bunch of CString objects.

Answer 1

CString is an alias of the CStringT class template. Objects of this class are really better not to pass to the DLL. The character type of the string class can be TCHAR (for both ANSI and Unicode character strings - see explanation below). The definition of CString (and CStringT ) can most likely be found in the atlstr.h header file.

LPTSTR is a regular pointer to a sequence of characters. The data type ( TCHAR* ) depends on the settings of the development environment: if the "Use Unicode Character set" option is selected, the TCHAR data type will be wchar_t (and LPTSTR will be wchar_t* , respectively). If the "Use Multi-byte character set" is selected, the TCHAR will be defined as char (and LPTSTR will be char* ).

So the question about interchangeability between CString and LPTSTR is not so simple. It also depends on how the DLL is written. If the DLL was designed with the same environment settings as the main program, then CString and LPTSTR can really be interchangeable.

Also, remember that CStirng is a class with many methods, while LPTSTR is just a pointer.