HDF5 : storing NumPy data
HDF5 takes care of binary compatibility of structures for you.  You simply have to tell it what your structs consist of (dtype) and you'll have no problems saving/reading record arrays - this is because the type system is basically 1:1 between numpy and HDF5.  If you use H5py I'm confident to say the IO should be fast enough provided you use all native types and large batched reads/writes - the entire dataset of allowable.  After that it depends on chunking and what filters (shuffle, compression for example) - it's also worth noting sometimes those can speed up by greatly reducing file size so always look at benchmarks.  Note that the the type and filter choices are made on the end creating the HDF5 document.
If you're trying to parse HDF5 yourself, you're doing it wrong.  Use the C++ and C apis if you're working in C++/C.  There are examples of so called "compound types" on the HDF5 groups website.
when I used NumPy I stored it's data in the native format *.npy. It's very fast and gave me some benefits, like this one

I could read *.npy from C code as
simple binary data(I mean *.npy are
binary-compatibly with C structures)

Now I'm dealing with HDF5 (PyTables at this moment). As I read in the tutorial, they are using NumPy serializer to store NumPy data, so I can read these data from C as from simple *.npy files?
Does HDF5's numpy are binary-compatibly with C structures too?
UPD :
I have matlab client reading from hdf5, but don't want to read hdf5 from C++ because reading binary data from *.npy is times faster, so I really have a need in reading hdf5 from C++ (binary-compatibility)
So I'm already using two ways for transferring data - *.npy (read from C++ as bytes,from Python natively) and hdf5 (access from Matlab)
And if it's possible,want to use the only one way - hdf5, but to do this I have to find a way to make hdf5 binary-compatibly with C++ structures, pls help, If there is some way to turn-off compression in hdf5 or something else to make hdf5 binary-compatibly with C++ structures - tell me where i can read about it...