Link Error 2028 2029 when using CString in C++/CLI

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sebastian.dau@googlemail.com - 01 Jun 2007 17:02 GMT

Hello Newsgroup,

I have a link error that I did not manage to fix.

I basically consume a VC 8.0 C++ dll that exports a class with a
method containing CString declaration as follows:

class WarnErr
{
//...
CString WarnErr::getReadableCode (long nCode)
{
//...
}

When using the method in another project (C++/CLI) to write a RTCW,
the linker fails with the following error:

Error 2 error LNK2028: unresolved token (0A00000F) "public: static
class ATL::CStringT<char,class StrTraitMFC_DLL<char,class
ATL::ChTraitsCRT<char> > > __cdecl
lala_McsOOP::WarnErr::getReadableCode(long)" (?
getReadableCode@WarnErr@lala_McsOOP@@$$FSA?AV?$CStringT@DV?
$StrTraitMFC_DLL@DV?$ChTraitsCRT@D@ATL@@@@@ATL@@J@Z) referenced in
function "public: class System::String ^ __clrcall
lala::Spectrometer::RTCW::SpectrometerException::ToString(void)" (?
ToString@SpectrometerException@RTCW@Spectrometer@lala@@$$FQ$AAMP
$AAVString@System@@XZ) SpectrometerException.obj

Does anybody know how to fix this issue. Or is there any other good
practice passing strings from unmanaged libs tto managed libs?

Thanks for your help!

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Ben Voigt [C++ MVP] - 01 Jun 2007 20:14 GMT

> When using the method in another project (C++/CLI) to write a RTCW,
> the linker fails with the following error:
[quoted text clipped - 12 lines]
> Does anybody know how to fix this issue. Or is there any other good
> practice passing strings from unmanaged libs tto managed libs?

I suggest that the only things you should pass across module boundaries are:
(1) blocks of raw data (pointer and length)
(2) interface pointers
DCOM shows that by following these two rules you can have very powerful yet
stable interaction between all kinds of different components. Decoupling in
this way is also good for encapsulation, testability, and stability.

Trying to share class objects between unmanaged modules usually fails due to
ODR violations.

> Thanks for your help!

Reply to this Message

sebastian.dau@googlemail.com - 04 Jun 2007 09:18 GMT

> > When using the method in another project (C++/CLI) to write a RTCW,
> > the linker fails with the following error:
[quoted text clipped - 24 lines]
>
> > Thanks for your help!

Hello Ben,

thanks for your comment on this issue. I generally agree with your
opinion as it is good practice.
However, there a couple of good reasons for CString as well and I was
under the opinion that passing basic types like strings isn't a big
deal anymore.
Let us consider the lib I'm trying to incorporate with is sort of fix
and will only get subject for changes if any other approach fails.

Can you point me to pretty good practices of passing strings of
individual length's from unmanaged code to C++/CLI code?

Thanks again,

Sebastian Dau

Reply to this Message

Ben Voigt [C++ MVP] - 04 Jun 2007 14:30 GMT

>> > Does anybody know how to fix this issue. Or is there any other good
>> > practice passing strings from unmanaged libs tto managed libs?
[quoted text clipped - 27 lines]
> Can you point me to pretty good practices of passing strings of
> individual length's from unmanaged code to C++/CLI code?

First up, you must compile all code using the unmanaged DLL's classes
without /clr and with the same compiler version used by the DLL. Otherwise
the ODR is violated. This is not a recommendation, it is an absolute
requirement to get any sort of reasonable behavior.

Next, you should use fundamental types such as wchar_t* or char* to pass
data between those files compiled without /clr and the ones compiled with.
The definition of those types aren't changed by /clr or the compiler
version. These convert to and from the std::string and CString variants in
the usual way.

Then, use the following functions to get the data to/from .NET
System::String:

PtrToStringChars
System::Runtime::InteropServices::Marshal::PtrToString{Ansi|Auto|BSTR|Uni}

If you do that, everything should link and run without problems. If the DLL
was compiled using an earlier version of the compiler, then the static lib
wrappers described in "First up" should use extern "C" functions. You
should probably do that anyway.

> Thanks again,
>
> Sebastian Dau

Reply to this Message

sebastian.dau@googlemail.com - 04 Jun 2007 15:56 GMT

> >> > Does anybody know how to fix this issue. Or is there any other good
> >> > practice passing strings from unmanaged libs tto managed libs?
[quoted text clipped - 53 lines]
>
> > Sebastian Dau

Thanks, Ben I'll give that a try and see how it works.

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Link Error 2028 2029 when using CString in C++/CLI

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