Reading any compound type to memory

[belugum]

Hi,

Similarly to #452, I'm trying to read a compound type unknown at compile time to memory and handle it dynamically.
I can successfully find information about the compound type using HighFive::CompoundType::getMembers(). But I can't read the data.
With the following code:

std::vector<uint8_t> v;

v.resize(dataset.getStorageSize());
dataset.read(v.data());

I get this error:

HDF5-DIAG: Error detected in HDF5 (1.10.7) thread 1:
  #000: ../../../src/H5Dio.c line 198 in H5Dread(): can't read data
    major: Dataset
    minor: Read failed
  #001: ../../../src/H5Dio.c line 463 in H5D__read(): unable to set up type info
    major: Dataset
    minor: Unable to initialize object
  #002: ../../../src/H5Dio.c line 977 in H5D__typeinfo_init(): unable to convert between src and dest datatype
    major: Dataset
    minor: Feature is unsupported
  #003: ../../../src/H5T.c line 4680 in H5T_path_find(): can't find datatype conversion path
    major: Datatype
    minor: Can't get value
  #004: ../../../src/H5T.c line 4893 in H5T__path_find_real(): no appropriate function for conversion path
    major: Datatype
    minor: Unable to initialize object
terminate called after throwing an instance of 'HighFive::DataSetException'
  what():  Error during HDF5 Read. 

I tried other methods that either didn't compile or had similar errors.

I found that the H5::DataSet::read method from the HDF5 C++ API only needs a void* and the DataType, that would suit my need. Is there any equivalent in HighFive? Or another method to read a compound type dynamically (without registering a type)?

Thanks!

[1uc]

If you have a HighFive::DataType, you could probably use dset.read(ptr, datatype):
https://bluebrain.github.io/HighFive/class_high_five_1_1_slice_traits.html#a308151100e49985c077608619302c6c0

Looking at the code, I think it might work, depending on whether void is considered to be const. See,

HighFive/include/highfive/bits/H5Slice_traits_misc.hpp

Lines 216 to 234 in 3addda4

	template <typename Derivate>
	template <typename T>
	inline void SliceTraits<Derivate>::read(T* array,
	const DataType& mem_datatype,
	const DataTransferProps& xfer_props) const {
	static_assert(!std::is_const<T>::value,
	"read() requires a non-const structure to read data into");
	const auto& slice = static_cast<const Derivate&>(*this);
	if (H5Dread(details::get_dataset(slice).getId(),
	mem_datatype.getId(),
	details::get_memspace_id(slice),
	slice.getSpace().getId(),
	xfer_props.getId(),
	static_cast<void*>(array)) < 0) {
	HDF5ErrMapper::ToException<DataSetException>("Error during HDF5 Read.");
	}
	}

The other semi-pragmatic answer is that what you're asking for is very close to the HDF5 C API. Maybe just use it directly? You can get the required HID from HighFive objects by calling .getId().

Please let me know if these don't work, or if anything was left uncovered.