I have created a very simple HDF5 file on my machine A, which has the HDF5 library v1.14.3 installed. It works fine, i.e. I can read it in in my program, and I can use h5dump, h5debug normally.
Then I copy it to a machine B with the HDF5 library v1.8.12 installed. This does not work at all, i.e. even h5debug will not recognize it as an HDF5 file:
$ h5debug file.hdf5
HDF5-DIAG: Error detected in HDF5 (1.8.12) thread 0:
#000: ../../src/H5F.c line 1585 in H5Fopen(): unable to open file
major: File accessibilty
minor: Unable to open file
#001: ../../src/H5F.c line 1376 in H5F_open(): unable to read superblock
major: File accessibilty
minor: Read failed
#002: ../../src/H5Fsuper.c line 336 in H5F_super_read(): file signature not found
major: File accessibilty
minor: Not an HDF5 file
cannot open file
Can I somehow make the file more compatible with older version when I create it on machine A? Or do I need to update the HDF5 library on machine B?
We have a forward/backward compatibility policy that governs library behavior when accessing files generated with a different format specification version. A lot of detail can be found in this RFC.
The gist is this:
(Backward) Newer library versions can access all earlier versions, i.e., v1.14.3 is happy with everything that came before.
(Forward) Older library versions can access HDF5 files “from the future” if they do not contain file format features unavailable with the older library version, i.e., accessing a 1.14.3 generated file with 1.8.12 should be fine as long as there’s nothing “fancier” going on.
However, your error message suggests that something else is going on:
#002: ../../src/H5Fsuper.c line 336 in H5F_super_read(): file signature not found
What do you see if you run this command:
od -c example.h5 | head -n 1
It should look like this:
0000000 211 H D F \r \n 032 \n 003 \b \b \0 \0 \0 \0 \0
The signature is the first 8 bytes 211 H D F \r \n 032 \n and the same for all specification versions.
Thank you for the detailed information and the link, I was not aware of the policy.
When using the suggested od command, I actually noticed that the file was empty. I then noticed this only happened after trying to read in, and then I found the actual problem: I had a copy&paste error in my code, I opened the file with the Overwrite tag instead of ReadOnly etc.
Sorry for that. And thank you in any case, you prevented me from testing a whole lot of other things before noticing this particular stupidity of mine.
