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

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H5FDioc.h File Reference
`#include "H5FDpublic.h"`

## Data Structures
struct | H5FD_ioc_config_t
| Configuration structure for H5Pset_fapl_ioc() / H5Pget_fapl_ioc(). More...

## Macros
#define | H5FD_IOC (H5OPEN H5FD_IOC_id_g)
#define | H5FD_IOC_CURR_FAPL_VERSION 1
#define | H5FD_IOC_DEFAULT_THREAD_POOL_SIZE 4
#define | H5FD_IOC_FAPL_MAGIC 0xFED21331
#define | H5FD_IOC_NAME "ioc"
#define | H5FD_IOC_THREAD_POOL_SIZE "H5FD_IOC_THREAD_POOL_SIZE"

## Functions
H5_DLL herr_t | H5Pget_fapl_ioc (hid_t fapl_id, H5FD_ioc_config_t *config_out)
| Queries a File Access Property List for H5FD_IOC file driver properties.
H5_DLL herr_t | H5Pset_fapl_ioc (hid_t fapl_id, H5FD_ioc_config_t *vfd_config)
| Modifies the specified File Access Property List to use the H5FD_IOC driver.

## Macro Definition Documentation

## ◆ H5FD_IOC

#define H5FD_IOC (H5OPEN H5FD_IOC_id_g)

Macro that returns the identifier for the H5FD_IOC driver. Returns a file driver identifier if successful; otherwise returns H5I_INVALID_HID.

Since
  1.14.0

## ◆ H5FD_IOC_CURR_FAPL_VERSION

#define H5FD_IOC_CURR_FAPL_VERSION 1

The version number of the H5FD_ioc_config_t configuration structure for the H5FD_IOC driver

## ◆ H5FD_IOC_DEFAULT_THREAD_POOL_SIZE

#define H5FD_IOC_DEFAULT_THREAD_POOL_SIZE 4

The default number of I/O concentrator worker threads

## ◆ H5FD_IOC_FAPL_MAGIC

#define H5FD_IOC_FAPL_MAGIC 0xFED21331

Unique number used to distinguish the H5FD_IOC driver from other HDF5 file drivers

## ◆ H5FD_IOC_NAME

#define H5FD_IOC_NAME "ioc"

The canonical name for the H5FD_IOC driver

Since
  1.14.0

## ◆ H5FD_IOC_THREAD_POOL_SIZE

#define H5FD_IOC_THREAD_POOL_SIZE "H5FD_IOC_THREAD_POOL_SIZE"

Macro for name of the environment variable that controls/overrides the number of I/O concentrator worker threads

The value set for this environment variable is interpreted as an int value and must be > 0.