How to access all the elements at once in boost circular buffer?

Question

I declared a buffer of vector in c++:

boost::circular_buffer<std::vector<float>> poses {20};

I need to store the values of the buffer into a tensor of shape [1, 20, 30]. Each vector in the buffer is of size 30. So the circular buffer has 20 size with each buffer having 30 values.

How do I store values in the buffer to tensor at once?