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| HDF5 Last Updated on 2026-07-28 The HDF5 Field Guide

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Definitions
VOL connector (H5VL)

## Detailed Description

## Macros
#define | H5VL_OPT_QUERY_SUPPORTED 0x0001
#define | H5VL_VERSION 3
| Version number of VOL class struct & callbacks.

## Typedefs
typedef int | H5VL_class_value_t
| VOL connector identifiers.

## Enumerations
enum | H5VL_subclass_t { H5VL_SUBCLS_NONE , H5VL_SUBCLS_INFO , H5VL_SUBCLS_WRAP , H5VL_SUBCLS_ATTR , H5VL_SUBCLS_DATASET , H5VL_SUBCLS_DATATYPE , H5VL_SUBCLS_FILE , H5VL_SUBCLS_GROUP , H5VL_SUBCLS_LINK , H5VL_SUBCLS_OBJECT , H5VL_SUBCLS_REQUEST , H5VL_SUBCLS_BLOB , H5VL_SUBCLS_TOKEN }

## Macro Definition Documentation

## ◆ H5VL_OPT_QUERY_SUPPORTED

#define H5VL_OPT_QUERY_SUPPORTED 0x0001

Flags to return from H5VLquery_optional API and 'opt_query' callbacks

Operations which access multiple objects' data or metadata in a container should be registered as file-level optional operations. (e.g. "H5Dwrite_multi" takes a list of datasets to write data to, so a VOL connector that implemented it should register it as an optional file operation, and pass-through VOL connectors that are stacked above the connector that registered it should assume that dataset elements for any dataset in the file could be written to) VOL connector supports this operation

Since
  1.14.0

## ◆ H5VL_VERSION

#define H5VL_VERSION 3

Version number of VOL class struct & callbacks.

Each VOL connector must set the 'version' field in the H5VL_class_t struct to the version of the H5VL_class_t struct that the connector implements. The HDF5 library will reject connectors with incompatible structs.

## Typedef Documentation

## ◆ H5VL_class_value_t

typedef int H5VL_class_value_t

VOL connector identifiers.

Values 0 through 255 are for connectors defined by the HDF5 library. Values 256 through 511 are available for testing new connectors. Subsequent values should be obtained from the HDF5 development team at help@.nosp@m.hdfg.nosp@m.roup..nosp@m.org.

## Enumeration Type Documentation

## ◆ H5VL_subclass_t

enum H5VL_subclass_t

Enum type for each VOL subclass (Used for various queries, etc)

Enumerator
H5VL_SUBCLS_NONE | Operations outside of a subclass
H5VL_SUBCLS_INFO | 'Info' subclass
H5VL_SUBCLS_WRAP | 'Wrap' subclass
H5VL_SUBCLS_ATTR | 'Attribute' subclass
H5VL_SUBCLS_DATASET | 'Dataset' subclass
H5VL_SUBCLS_DATATYPE | 'Named datatype' subclass
H5VL_SUBCLS_FILE | 'File' subclass
H5VL_SUBCLS_GROUP | 'Group' subclass
H5VL_SUBCLS_LINK | 'Link' subclass
H5VL_SUBCLS_OBJECT | 'Object' subclass
H5VL_SUBCLS_REQUEST | 'Request' subclass
H5VL_SUBCLS_BLOB | 'Blob' subclass
H5VL_SUBCLS_TOKEN | 'Token' subclass