What is a good way to tell a netCDF4 file from a "regular" HDF5 file?

[krisfed]

I was originally intending to use nc_open and check the status, but it seems to work fine on HDF5 files (that are NOT netCDF4 files), and return a reasonable-looking ncid.

Even nc_inq_format seems to think a "regular" HDF5 file is a netCDF4 file (NC_FORMAT_NETCDF4).

My next best idea is to check for the presence of _NCProperties global attribute with something like nc_inq_att. This seems to work (works fine on a netCDF4 file and returns a NC_ENOTATT error status on a "regular" HDF5 file), but I am wondering if there is a better way.

Is a _NCProperties global attribute guaranteed to be present for all valid netCDF4 files? Should I be using something else?

I am working with v4.9.2 if it matters.

Thanks!

[DennisHeimbigner]

Is a _NCProperties global attribute guaranteed to be present for all valid netCDF4 files?

This mostly a good way to tell the difference. There is a couple of issues, though.
First, the _NCProperties attribute was added in netcdf-c version 4.4.1-RC2 - May 13, 2016.
So files created before than (and there are probably a lot of them) will not have _NCProperties defined.
Second, I have recollection that there is python package wrapping HDF5 that also attempts to
add _NCProperties to its files. It can be distinguished by the (key,value) pairs of that attribute, but I am not
off hand sure what pairs it defines.

[krisfed]

Thank you, Dennis! Would you recommend using something else, or is _NCProperties pretty much the best option (even if it is not 100% accurate)?