Solved by leowalkling in post #3 
              
              
                I forgot to mention, that I used the CMake package in site-packages/torch/share/cmake to specify the PyTorch dependency: 
target_link_libraries(torch_plus_ops ${TORCH_LIBRARIES}). 
_C.lib does not define the symbol either. Also, when using __declspec(dllexport), the linker would not look for the sym…