How to convert PyTorch tensor to C++ torch::Tensor vice versa?

Hi, I am working on a project which need transfer the Pytorch tensor to libtorch and vice versa.
I already knew that it may need following functions :

PyObject * THPVariable_Wrap(at::Tensor t);
at::Tensor& THPVariable_Unpack(PyObject* obj);

However, I tried use them like these:

void receive_tensor_from_py(PyObject* obj){
  at::Tensor &t = THPVariable_Unpack(obj);
  std::cout << &t << std::endl;

But it doesn’t work, can anyone gives a small sample code?