.npy is the standard NumPy file format for saving arrays to disk with the full information about them. .npz is the standard format for persisting multiple NumPy arrays on disk. A .npz file is a zip file containing multiple .npy files, one for each array.
libnpy is a simple C++ library for reading and writing of NumPy's .npy files.
The Npy package is a basic C++ wrapper for .npy/.npz file format. For ease of use, a simple example is included.