h5readatt

Read attribute from HDF5 file

Syntax

attval = h5readatt(filename,loc,attr)

Description

attval = h5readatt(filename,loc,attr) retrieves the value of the specified attribute from the specified location in an HDF5 file.

Examples

Read Group Attributes

Read the attribute attr2 from the root group of the HDF5 file example.h5.

val = h5readatt('example.h5','/','attr2')

val = 2×2 int32 matrix

   0   2
   1   3

Read Dataset Attributes

Read the attribute units from the dataset lon in the HDF5 file example.h5.

val = h5readatt('example.h5','/g4/lon','units')

val = 
'degrees_east'

Input Arguments

filename — Filename

string scalar | character vector

Filename of an existing HDF5 file, specified as a string scalar or character vector.

Depending on the location of your file, filename can take one of these forms.

Location	Form
Current folder or folder on the MATLAB® path	If the file is in the current folder or in a folder on the MATLAB path, then specify the name of the file in filename. Example: "myFile.h5"
Other folders	If the file is neither in the current folder nor in a folder on the MATLAB path, then specify the full or relative path in filename. Example: "C:\myFolder\myFile.h5" Example: "myFolder\myFile.h5"
Uniform resource locator (URL) (since R2024b)	If the file is located by an internet URL, then filename must contain the protocol type, such as http://. For more information, see Work with Remote Data. Example: "http://my_hostname/my_path/my_file.h5"
Remote location	If the file is stored at a remote location, then filename must contain the full path of the file specified as a uniform resource locator (URL) of the form: scheme_name://path_to_file/filename Based on your remote location, scheme_name can be one of the values in this table. Remote Location scheme_name Amazon S3™ s3 Windows Azure® Blob Storage wasb, wasbs HDFS™ hdfs For more information, see Work with Remote Data. Example: "s3://myBucket/myFolder/myFile.h5"

• If your file consists of several physical files using the Family driver, specify filename using a format specifier. If these physical files are not in your current folder, then specify them using their full or relative path. For example, to use the Family driver with the two files family0.h5 and family1.h5 in your current folder, specify filename as "family%d.h5".

• If your file consists of several physical files using the Multi driver or the Split driver, specify filename as the leading prefix of the names of the physical files. If these physical files are not in your current folder, then specify them using their full or relative path. For example, to use the Multi driver with the six files multi-b.h5, multi-g.h5, multi-l.h5, multi-o.h5, multi-r.h5, and multi-s.h5 in your current folder, specify filename as "multi".

loc — Location in file

character vector | string scalar

Location in the file, specified as a character vector or string scalar containing the full path of an existing group or dataset to which the attribute belongs. To read an attribute from the root group of the file, specify '/' as the location.

attr — Attribute name

character vector | string scalar

Attribute name, specified as a character vector or string scalar containing the name of an attribute belonging to a group or dataset.

Limitations

• MATLAB does not support internet URLs that require authentication.

• MATLAB Online™ supports internet URLs associated with Microsoft^® OneDrive™ files and folders, while the installed version of MATLAB supports only local OneDrive files.

• The h5readatt function issues an error for attributes and datasets that fail file integrity checks. To read attributes in such situations, use the H5P.set_relax_file_integrity_checks function and the low-level HDF5 interface. (since R2024b)

Version History

Introduced in R2011a

R2024b: Attributes and datasets that fail file integrity checks no longer supported (R2024b Update)

The h5readatt function now issues an error for attributes and datasets that fail file integrity checks. Previously, this function did not issue an error for such attributes or datasets. To read attributes in such situations, use the H5P.set_relax_file_integrity_checks function and the low-level HDF5 interface. This table shows how to update your code to use the low-level HDF5 interface.

R2024a and Earlier	Starting in R2024b
myAttrValue = h5readatt("myFilename.h5","myDatasetName","myAttrName");	fapl = H5P.create("H5P_FILE_ACCESS"); H5P.set_relax_file_integrity_checks(fapl,"H5F_RFIC_UNUSUAL_NUM_UNUSED_NUMERIC_BITS") fid = H5F.open("myFilename.h5","H5F_ACC_RDONLY",fapl); dset_id = H5D.open(fid,"myDatasetName"); attrID = H5A.open(dset_id,"myAttrName"); myAttrValue = H5A.read(attrID); H5A.close(attrID) H5D.close(dset_id) H5F.close(fid) H5P.close(fapl)

R2024b: Read attributes from HDF5 files over HTTP and HTTPS

You can read attributes from HDF5 files stored in primary online sources by using the h5readatt function with an internet URL.

R2020b: Read attributes from HDF5 files at a remote location

You can read attributes from HDF5 files in remote locations, such as Amazon S3, Windows Azure Blob Storage, and HDFS.

R2020b: Read attributes from HDF5 files with Unicode names

You can read attributes from HDF5 files whose names are encoded as Unicode characters.

R2020a: Read nonscalar string attributes as MATLAB string arrays

h5readatt returns HDF5 string array attributes as MATLAB string arrays rather than cell arrays of character vectors. Single (scalar) HDF5 string attributes are returned as MATLAB character vectors.