Re: Exposing classes via __declspec(dllexport)

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Fri, 07 Aug 2009 12:28:00 -0400

Message-ID:

<u57wJw3FKHA.2832@TK2MSFTNGP03.phx.gbl>

Jason Newell wrote:

As soon as I sent my OP, I realized that I didn't spell out that I had
converted the project from .dll to static lib. I also realized after OP
that __declspec(dllexport) wasn't really needed since I made that
conversion.

I will certainly research more based off your suggestion. Your response
is using terminology that I need to equate to code so I'll have to try
and google for examples because right off hand I have no idea how to
implement what you've suggested. I appreciate the pointers (no pun
intended).

This is my code in the DLL

..h file

extern "C" __declspec(dllexport) IReader* CreateReader();
extern "C" __declspec(dllexport) void DestroyReader(IReader* pReader);

..cpp file

IReader* CreateReader()
{
return new CReader;
}

void DestroyReader(IReader* pReader)
{
delete static_cast<CReader*>(pReader);
}

The class CReader is a concrete class derived from interface IReader. Note that
IReader does not need either a constructor or destructor (that is the reason for
the cast in DestroyReader()). The client application does not know anything
about CReader.

My DLL's are actually plugins, so the exports are accessed via LoadLibrary() and
GetProcAddress(), not via an import library. Each plugin implements a different
concrete class CReader.

--
David Wilkinson
Visual C++ MVP