[Dev-C++] DLL and C++ classes

[<or...@vp...>]

Hi!

All right C++ gurus out there: here is the opportunity to show yourself!
I really need some help.

I have C++ classes exported and compiled into a DLL. Like:

#ifdef BUILD_DLL
#  define MY_API __declspec(dllexport)
#else
#  define MY_API __declspec(dllimport)
#endif

class MY_API MyClass
{
   MyClass();
   /* ... */
}

So, the DLL and the .def file is created fine. (BUILD_DLL=1)
BUT, when I use it (BUILD_DLL=0), it sais undefined reference to 
MyClass::MyClass
I have LOTS of things exported apart from this, most works, but "some" 
are not found. They are not even in the .def file. BUT if I specify 
--export-all-symbols, my DLL and program works.

I don't seem to fully understand why this happens.
I have been lurking over the net for 3 hours by now, but still haven't 
found anything of value.
Please help me, if you know anything about this. Thank you!

--
Greetings,
   Balázs