Re: vftable not found when __declspec(dllimport) used

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Fri, 21 Nov 2008 20:55:17 -0500

Message-ID:

<e8d7cVETJHA.6060@TK2MSFTNGP06.phx.gbl>

BoHuang wrote:

I have class RTRTwrapper implementing an abstract class PluginInterface with
pure virtual functions.

This is a DLL project so RTRTwrapper is declared as
class __declspec(dllimport) RTRTwrapper : public PluginInterface

When building, I get

Error 53 error LNK2019: unresolved external symbol "__declspec(dllimport)
const RTRTwrapper::`vftable'" (__imp_??_7RTRTwrapper@@6B@) referenced in
function "public: __thiscall RTRTwrapper::RTRTwrapper(void)"
(??0RTRTwrapper@@QAE@XZ) RTRTwrapper.obj

Moreover, I get alot of:
2>..\..\RTRT_dll\RTRTwrapper.cc(42) : warning C4273:
'RTRTwrapper::getManipulator' : inconsistent dll linkage

Just for tests, I do not get any linking error if I use any of the follow
declaration:

//class __declspec(dllexport) RTRTwrapper : public PluginInterface

//class RTRTwrapper : public PluginInterface

I do get the same linking error if using:
//class __declspec( dllimport ) RTRTwrapper

What am I doing wrong? When should I use dllexport instead?

BoHuang:

This may not be relevant to your question, but if you are creating plugin DLL's
with a pure abstract base class (interface), you do not normally export classes,
rather you export factory methods for creating those classes.

The whole point of a plugin architecture is that the client application does not
know about the available plugins at compile time.

--
David Wilkinson
Visual C++ MVP