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| HDF5 Last Updated on 2025-11-11 The HDF5 Field Guide

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API Directory Reference

## Detailed Description

This directory contains several test applications that exercise HDF5's public API and serve as regression tests for HDF5 VOL Connectors.

# Build Process and options

These HDF5 API tests are enabled by default, but can be disabled by passing the `-DHDF5_TEST_API=OFF` option to CMake. The following build options are available to influence how the API tests get built:

## CMake

To set an option, it should be prepended with `-D` when passed to the `cmake` command. For example,

    cmake -DHDF5_TEST_API=OFF ..

`HDF5_TEST_API` (Default: `ON`) - Determines whether the API tests will be built.

`HDF5_TEST_API_INSTALL` (Default: `OFF`) - Determines whether the API tests should be installed on the system.

`HDF5_TEST_API_ENABLE_ASYNC` (Default: `OFF`) - Determines whether tests for HDF5's asynchronous I/O capabilities should be enabled. Note that the "native" HDF5 VOL connector doesn't support this functionality, so these tests are directed towards VOL connectors that do.

`HDF5_TEST_ENABLE_DRIVER` (Default: `OFF`) - Determines whether the API test driver program should be built. This driver program is useful when a VOL connector relies upon a server executable (as well as possible additional executables) in order to function. The driver program can be supplied with a server executable and server/client arguments to use when running the API tests.

`HDF5_TEST_API_SERVER` (Default: empty string) - If `HDF5_TEST_ENABLE_DRIVER` is set to `ON`, this option should be edited to point to the server executable that the driver program should attempt to launch before running the API tests.

## Autotools

Currently unsupported

## Usage

These API tests currently only support usage with the native HDF5 VOL connector and HDF5 VOL connectors that can be loaded dynamically as a plugin. For information on how to build a VOL connector in this manner, refer to section 2.3 of the HDF5 VOL Connector Author Guide.

If an HDF5 VOL connector has been built alongside the library, these API tests can be used for testing that VOL connector at the same time that HDF5 is test. For more information on how to build a VOL connector alongside the HDF5 library, refer to Building and testing HDF5 VOL connectors with CMake FetchContent.

These API tests can also be used to test an HDF5 VOL connector that is external to the library. For convenience, the `HDF5_TEST_API_INSTALL` option can be used to install these tests on the system where other HDF5 executables (such as `h5dump`) are installed. To run these tests manually with your VOL connector, set the following two environment variables:

`HDF5_VOL_CONNECTOR` - This environment variable should be set to the name chosen for the VOL connector to be used. For example, HDF5's DAOS VOL connector uses the name "[daos](https://github.com/HDFGroup/vol-daos/blob/v1.2.0/src/daos_vol.h#L30)" and would therefore set:

    HDF5_VOL_CONNECTOR=daos

`HDF5_PLUGIN_PATH` - This environment variable should be set to the directory that contains the built library for the VOL connector to be used.

Once these are set, the HDF5 API tests will attempt to automatically load the specified VOL connector and use it when running tests. If HDF5 is unable to locate or load the VOL connector specified, it will fall back to running the tests with the native HDF5 VOL connector and an error similar to the following will appear in the test output:

    HDF5-DIAG: Error detected in HDF5 (X.XX.X) MPI-process 0:
      #000: /home/user/git/hdf5/src/H5.c line 1010 in H5open(): library initialization failed
        major: Function entry/exit
        minor: Unable to initialize object
      #001: /home/user/git/hdf5/src/H5.c line 277 in H5_init_library(): unable to initialize vol interface
        major: Function entry/exit
        minor: Unable to initialize object
      #002: /home/user/git/hdf5/src/H5VLint.c line 199 in H5VL_init_phase2(): unable to set default VOL connector
        major: Virtual Object Layer
        minor: Can't set value
      #003: /home/user/git/hdf5/src/H5VLint.c line 429 in H5VL__set_def_conn(): can't register connector
        major: Virtual Object Layer
        minor: Unable to register new ID
      #004: /home/user/git/hdf5/src/H5VLint.c line 1321 in H5VL__register_connector_by_name(): unable to load VOL connector
        major: Virtual Object Layer
        minor: Unable to initialize object

## Help and Support

For help with building or using the HDF5 API tests, please contact the HDF Help Desk.