g++ -c com_main.cpp -o com_main.o -Wall -g 
In file included from com_main.cpp:4:
com_main.h:15: error: conflicting return type specified for `virtual ULONG CTest::QueryInterface(const IID&, void**)'
c:/msys/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/unknwn.h:26: error:   overriding `virtual HRESULT IUnknown::QueryInterface(const IID&, void**)'
make: *** [com_main.o] Error 1