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| HDF5 Last Updated on 2026-03-23 The HDF5 Field Guide

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H5FD_ioc_config_t Struct Reference

`#include <src/H5FDsubfiling/H5FDioc.h>`

## Detailed Description

Configuration structure for H5Pset_fapl_ioc() / H5Pget_fapl_ioc().

H5FD_ioc_config_t is a public structure that is used to pass configuration data to the H5FD_IOC driver via a File Access Property List. A pointer to an instance of this structure is a parameter to H5Pset_fapl_ioc() and H5Pget_fapl_ioc().

## Data Fields
uint32_t | magic
int32_t | thread_pool_size
uint32_t | version

## Field Documentation

## ◆ magic

uint32_t magic

A somewhat unique number which distinguishes the H5FD_IOC driver from other drivers. Used in combination with a version number, it can help to validate a user-generated File Access Property List. This field should be set to H5FD_IOC_FAPL_MAGIC.

## ◆ thread_pool_size

int32_t thread_pool_size

The number of I/O concentrator worker threads to use.

This value can also be set or adjusted with the H5FD_IOC_THREAD_POOL_SIZE environment variable.

## ◆ version

uint32_t version

Version number of the H5FD_ioc_config_t structure. Any instance passed to H5Pset_fapl_ioc() / H5Pget_fapl_ioc() must have a recognized version number or an error will be raised. Currently, this field should be set to H5FD_IOC_CURR_FAPL_VERSION.

The documentation for this struct was generated from the following file:

- src/H5FDsubfiling/H5FDioc.h