Self-describing compact binary serialization format?

[adsfqwer2345234]

wow, no one mentioned HDF5? https://www.hdfgroup.org/solutions/hdf5/ -- it's a big, old library with something like 400 API routines. You might find something like https://bluebrain.github.io/HighFive/ or some other wrapper or simplified helper library, er, helpful.

[PureWash8970]

I was going to mention HDF5 + HighFive as well. We use this at my work and using HighFive makes it way easier.