Re: error LNK2019 unresolved external: _AtlInitialConstruct

"Igor Tandetnik" <>
Tue, 25 Apr 2006 21:22:51 -0400
<> wrote in message

We are starting a new software project and have decided to use VS2005
as the development environment. We would like to use some existing
code that was built using Visual Studio 6. For the past few days I
have been loading some VS6 .dsp files into VS2005 and converting them
to .vcproj files. I have been quite successful in getting most DLL's
to compile and link with only having to make minor source code
changes. However, I have run into the following linker error when
building the main EXE which has stumped me and the other developers
in the group:

error LNK2019: unresolved external symbol "__declspec(dllimport)
public: long __thiscall ATL::CComObjectRootEx<class
referenced in function

The COM object is defined in another DLL as:

class __declspec(dllexport) ATL_NO_VTABLE CAurora :

You have exported a C++ class from a DLL, and are trying to import it
into an EXE. This only works when both modules are built with the same
version of the same compiler, using the same compiler settings. In other
words, it's usually a bad idea. Here, it appears that your DLL is built
with VC6 while you are building the EXE with VC8.

Why are you using C++ mechanisms for exporting and importing a class,
when it clearly implements a COM object. Why don't you use it as such?
COM is specifically designed for binary compatibility.
With best wishes,
    Igor Tandetnik

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