CString Error Compiling With Visual Studio.NET (VC7)

[Gaul]

Has anyone experienced CString problems re-compiling an existing application with VC.NET I got the following errors while re-compiling an existing application with VC.NET/VS7. The application compiles and works perfectly with VS6. Yes, I am aware of the new string library (atlstr.h), but was suprised to get compilation errors on the older MFC CString. class CString; ... ... (CString forward-declared in a header - no change from existing code) error C2371: 'CString' : redefinition; different basic types int DisplayRecord( _RecordsetPtr recordset, const CString& strFilterColumnName = "", const CString& strFilterColumnValue = "", const CString& strDupColumnName = "", const CString& strDateFormat = szFTDateFormat); C2440: 'default argument' : cannot convert from 'char [1]' to 'const CString &' When I re-compile the application with VS6, it works fine. I cannot imagine having to embark on a porting exercise just to remove all the older MFC CString references in my code. Has anyone experienced the same problems, and how did they resolve it. Gaul www.gaulles.com

[Jens Kreiensiek]

Hi, just wondering that it is possible to change the value of a const(!) ref. under VS6 ?!? cu, Jens

[Michael Dunn]

Here's my guess: Your error is that you're trying to create a reference to something that isn't a CString. If the parameter were a plain CString, the compiler could call the appropriate constructor when the function was called. But since creating a reference doesn't call a constructor, there's no way to convert from a char array to a CString. Look in the docs for a list of changes between VC6 and 7 and see if it mentions this. --Mike-- http://home.inreach.com/mdunn/ Sometimes, arming yourself with a big pointy stake just won't do you any good.

[Vagif Abilov]

It's generally a bad idea to convert one object (or type) to a reference to another object (unless there is an explicit operator for such conversion). While assignment CString str = "" works fine, statement CString& str = "" will lead to an error. Visual C++ 6.0 is based on older compiler version and does not react on many erroneous statements. VC++ Embedded 3.0 is much better in this respect. VC++ 7.0 is even newer, so it shouldn't be surprising that it is more strict. Win32/ATL/MFC Developer Oslo, Norway

[Gaul]

Those are default parameter values set for the function declaration in the header file. Works with VS6. Gaul www.gaulles.com

[Gaul]

What about the earlier error, reproduced below. CString is just the regular CString - no special class. class CString; ... ... (CString forward-declared in a header - no change from existing code) error C2371: 'CString' : redefinition; different basic types Gaul www.gaulles.com

[Gaul]

CString is just a regular CString - no special class. What about the following error: class CString; ... ... (regular CString forward-declared in a header - no change from existing code) error C2371: 'CString' : redefinition; different basic types Gaul www.gaulles.com

[Vagif Abilov]

I don't have with me VS.Net headers now, but if I remember it right, CString is no longer defined as class, it is template-based now. This will of course make compiler complain about forward-declaring CString as class. Forward declaration must match the actual declaration exactly: you can't refer struct and template as class. I advice you to take a closer look at VC header files. Spending some time on reading class library header files will save you many hours of work in the future. Good luck Vagif Win32/ATL/MFC Developer Oslo, Norway

[Mike Burston]

I haven't worked with .NET at all, so this may not be relevant! CString is actually two different types IN VC6 - depending upon the #define _UNICODE state it is either an 'char' container, or a 'wchar_t' container. It is possible to get the "redefinition; different basic types" error if you try to mix 'ASCII' and 'UNICODE' compiled files. Could the .NET error be some problem related to UNICODE and non-UNICODE code interacting ?

[Mike Burston]

Actually, just reviewing your post again I am fairly sure that this is a UNICODE problem! You are assigning default values to the parameters of the fuintion call. The default values are all ASCII string literals eg: const CString& param1 = "" If the default .NET compilation is UNICODE then this will fail, since you cannot initialise a UNICODE CString with an ASCII literal. For UNICODE, the code should read const CString& param1 = L"" Or, if you want to not worry about this: const CString& param1 = _T("") So, the bottom line is that the code you are trying to compile can ONLY be compiled in non-UNICODE mode - it is not UNICODE aware. Therefore, you have to make sure that .NET is not running in UNICODE mode (I assume it's an option ? Java only supports UNICODE, so there is no 'non-UNICODE' mode)