How to call a function by pointer in a struct from a shared library?

Hello.

I try to use a third-party shared library. It has a function, which returns a structure. This structure contains a function pointer. I don't understand how to call it. And loadlibrary shows warnings like this:

"The data type ' ULONG ( * AddRef ) ( IVciFifo * This ) ' used by structure IVciFifoVtbl does not exist. The structure

may not be usable"

Please, help