h5labview

The Hierarchical Data Format (HDF5) is a open-source, cross-platform, data storage solution originally developed at the National Center for Supercomputing Applications (NCSA) for storage of scientific data and descriptive meta-data in an organised heirarchy. This project extends the power of HDF5 to LabVIEW, which is potentially very useful in many applications.

This project provides HDF5 v1.10.4 functionality to LabVIEW 2010 or newer, and is available as a self-installing package (*.vip file), installable through the VI Package Manager, or the latest version can be installed directly from the repository.

The h5labview library has been stable for many years, providing direct access to HDF data I/O functionality. However, development of new functionality has ceased and the newer features of the HDF5 format may not be supported. Users are welcome to implement any missing functionality.

To demonstrate how easy it is to use h5labview, here's an example showing creation of a new HDF5 file and writing a dataset with an attribute inside a nested group. A screenshot from HDFView showing the hierarchy of the generated file and the dataset is shown to the right. As of version 2, h5labview supports compound datatypes (clusters) with "table" access, as demonstrated below.

The table below lists the datatypes supported by h5labview in version 2, and their state of implementation. See this FAQ entry on why not all types are planned to be supported.

LabVIEW type	HDF type	Notes
I8..I64	H5T_NATIVE_INT8 .. H5T_NATIVE_INT64	Native-endian numerical formats
U8..U64	H5T_NATIVE_UINT8 .. H5T_NATIVE_UINT64
SGL, DBL	H5T_NATIVE_FLOAT, H5T_NATIVE_DOUBLE
CSG, CDB	H5T_COMPOUND	Compound with "real" and "imag" components
EXT, CEX	Custom H5T_FLOAT	Host-compatible extended precision type1
Physical quantities	Committed H5T_FLOAT	Written in SI units as named compounds
U8..U64	H5T_BITFIELD	Read-only support for BITFIELD datatypes as unsigned integers
String	H5T_STRING	Both variable and fixed strings2
Boolean	H5T_ENUM	Enumeration of "false"=0 and "true"=1
Clusters	H5T_COMPOUND	Valid clusters may contain any of the above types
Arrays	Implemented as dataspaces3	Array can be of any dimension of above type, including clusters
Enums	H5T_ENUM	LabVIEW enums supported4
Images	As per specification	Writing of Grayscale, Truecolor and Palette images supported
Timestamps	H5T_COMPOUND	Direct translation of LabVIEW's internal timestamp format
Waveforms	Dataset with specific attributes	Currently only analog waveforms supported

Notes:
1. LabVIEW's memory layout for EXT varies across platforms, as does HDF's extended H5T_NATIVE_LDOUBLE. A custom HDF type is created corresponding to the EXT layout on the host machine and HDF performs conversions automatically. This should lead to no precision loss when writing, and enables reading at the greatest precision of the host. The procedure is detailed in this FAQ entry.
2. HDF supports two types of strings: fixed and variable length. Variable-length strings are implemented and used by default, but LabVIEW strings that contain the null character (\0) must be written as fixed strings. Whether a string is read/written as fixed or variable is configured in LabVIEW, as described in this FAQ entry.
3. Arrays are implemented in HDF5 with a separate "dataspace" interface. Although an array datatype does exists, the H5T_ARRAY is inefficient and serves limited purpose. The array datatype therefore will not be implemented, neither will arrays of arrays nor clusters including arrays.
4. LabVIEW defines enums as a set of contiguous unsigned integers. HDF5 sets no such restriction, so as such any LabVIEW enum can be written to an HDF file but HDF5 enums must be read as (signed) integers.