Migrating from 6.0 to .NET

[martin_craigen]

Hi,
I'm investigating how easy/difficult it will be to migrate from Visual C++ v6.0 to .NET.

I tried simply rebuilding one of our projects without modification, but got the WINVER problem. So I fixed that, then tried to build again...

This time, I got CString errors.

I looked up the HELP, and found Q309801 "PRB: Linking Errors When You Import CString-Derived Classes" (http://support.microsoft.com/default...;EN-US;Q309801). This suggests adding the following 2 lines to stdafx.h :-

template class __declspec(dllimport) CStringT<TCHAR, StrTraitMFC<TCHAR, ChTraitsCRT<TCHAR> > >;
template class __declspec(dllimport) CSimpleStringT<TCHAR>;

I added these lines, but I am still getting loads of CString errors in the build, e.g. :-

PeriodEdit.cpp(25) : error C2079: 'CScanString::MyString' uses undefined class 'CString'

(code is - "class CScanString : public CString")

I have looked for ages trying to find related threads with a solution. However, a lot of the relevant threads have been left hanging without a solution.

Does anyone know how to solve this CString problem?
(Is this the right forum for this question?)

[Andreas Masur]

Completely off the top of my head...'CString' is now a template class...thus...the following should work (hope I get it right)...

class CScanString : public CStringT<TCHAR, StrTraitMFC<TCHAR> >

[martin_craigen]

Andreas,
Thanks for your help.

That fixed the particular problem in the declaration.

However, now I get a failure a bit further down...

class CScanString : public CStringT<TCHAR, StrTraitMFC<TCHAR> >
{
friend class CString;
private:
CString MyString;

PeriodEdit.cpp(27) : error C2079: 'CScanString::MyString' uses undefined class 'CString'

It looks like I am going to have to do a lot of work getting our code to compile, as we use CStrings everywhere.

Has anyone else had this problem? I wouldn't have thought we are the first to hit this problem...

[Andreas Masur]

Well...you can of course 'typedef' around the problem...however, that seems to a little bit too much work...I actually do not have any .NET compiler installed somewhere (my annual Christmas installing party is coming up ), thus, I cannot try it for myself....sorry for that...

[zc0styn]

I've got the same errors (error C2027: use of undefined type 'CString'). What i don't understand is that i have a lot of application in VC++ 2003 that works fine using CString and my current project has lots of errors. Please let me know if you find a solution for this.

[martin_craigen]

zc0styn,
My problem was a "friend" declaration, described as follows :-


"friend class not required when derived from class"

Here is an example of a class derived from CString, but containing a redundant friend class CString :-

class CScanString : public CString
{
friend class CString;
private:
CString MyString;
const char *StartOfString;
public:
int ReadFloatNums(float**, char *);
int ReadPercentages(float**, char *);
const CScanString& operator=(const CString& stringSrc);
};

Trying to compile this in .NET gives error :-

error C2079: 'CScanString::MyString' uses undefined class 'CString'

Since the CScanString class is already based on CString, the friend declaration is redundant, and should be removed.