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

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Dataset Creation Properties
Property Lists (H5P) » Object Creation Properties

## Detailed Description

Use dataset creation properties to control aspects of dataset creation such as fill time, storage layout, compression methods, etc. Unlike dataset access and transfer properties, creation properties are stored with the dataset, and cannot be changed once a dataset has been created.

Dataset creation property list functions (H5P)
Function | Purpose
--- | ---
H5Pset_layout | Sets the type of storage used to store the raw data for a dataset.
H5Pget_layout | Returns the layout of the raw data for a dataset.
H5Pset_chunk | Sets the size of the chunks used to store a chunked layout dataset.
H5Pget_chunk | Retrieves the size of chunks for the raw data of a chunked layout dataset.
H5Pset_chunk_opts/H5Pget_chunk_opts | Sets/gets the edge chunk option setting from a dataset creation property list.
H5Pset_deflate | Sets compression method and compression level.
H5Pset_fill_value | Sets the fill value for a dataset.
H5Pget_fill_value | Retrieves a dataset fill value.
H5Pfill_value_defined | Determines whether the fill value is defined.
H5Pset_fill_time | Sets the time when fill values are written to a dataset.
H5Pget_fill_time | Retrieves the time when fill value are written to a dataset.
H5Pset_alloc_time | Sets the timing for storage space allocation.
H5Pget_alloc_time | Retrieves the timing for storage space allocation.
H5Pset_filter | Adds a filter to the filter pipeline.
H5Pall_filters_avail | Verifies that all required filters are available.
H5Pget_nfilters | Returns the number of filters in the pipeline.
H5Pget_filter | Returns information about a filter in a pipeline. The C function is a macro: See also API Compatibility Macros.
H5Pget_filter_by_id | Returns information about the specified filter. The C function is a macro: See also API Compatibility Macros.
H5Pmodify_filter | Modifies a filter in the filter pipeline.
H5Premove_filter | Deletes one or more filters in the filter pipeline.
H5Pset_fletcher32 | Sets up use of the Fletcher32 checksum filter.
H5Pset_nbit | Sets up use of the n-bit filter.
H5Pset_scaleoffset | Sets up use of the scale-offset filter.
H5Pset_shuffle | Sets up use of the shuffle filter.
H5Pset_szip | Sets up use of the Szip compression filter.
H5Pset_external | Adds an external file to the list of external files.
H5Pget_external_count | Returns the number of external files for a dataset.
H5Pget_external | Returns information about an external file.
H5Pset_char_encoding | Sets the character encoding used to encode a string. Use to set ASCII or UTF-8 character encoding for object names.
H5Pget_char_encoding | Retrieves the character encoding used to create a string.
H5Pset_virtual | Sets the mapping between virtual and source datasets.
H5Pget_virtual_count | Gets the number of mappings for the virtual dataset.
H5Pget_virtual_dsetname | Gets the name of a source dataset used in the mapping.
H5Pget_virtual_filename | Gets the filename of a source dataset used in the mapping.
H5Pget_virtual_srcspace | Gets a dataspace identifier for the selection within the source dataset used in the mapping.
H5Pget_virtual_vspace | Gets a dataspace identifier for the selection within the virtual dataset used in the mapping.
H5Pset_dset_no_attrs_hint/H5Pget_dset_no_attrs_hint | Sets/gets the flag to create minimized dataset object headers.

## Functions
htri_t | H5Pall_filters_avail (hid_t plist_id)
| Verifies that all required filters are available.
herr_t | H5Pfill_value_defined (hid_t plist, H5D_fill_value_t *status)
| Determines whether fill value is defined.
herr_t | H5Pget_alloc_time (hid_t plist_id, H5D_alloc_time_t *alloc_time)
| Retrieves the timing for storage space allocation.
int | H5Pget_chunk (hid_t plist_id, int max_ndims, hsize_t dim[])
| Retrieves the size of chunks for the raw data of a chunked layout dataset.
herr_t | H5Pget_chunk_opts (hid_t plist_id, unsigned *opts)
| Retrieves the edge chunk option setting from a dataset creation property list.
herr_t | H5Pget_dset_no_attrs_hint (hid_t dcpl_id, bool *minimize)
| Retrieves the setting for whether or not to create minimized dataset object headers.
herr_t | H5Pget_external (hid_t plist_id, unsigned idx, size_t name_size, char *name, HDoff_t *offset, hsize_t *size)
| Returns information about an external file.
int | H5Pget_external_count (hid_t plist_id)
| Returns the number of external files for a dataset.
herr_t | H5Pget_fill_time (hid_t plist_id, H5D_fill_time_t *fill_time)
| Retrieves the time when fill values are written to a dataset.
herr_t | H5Pget_fill_value (hid_t plist_id, hid_t type_id, void *value)
| Retrieves a dataset fill value.
H5Z_filter_t | H5Pget_filter1 (hid_t plist_id, unsigned filter, unsigned int *flags, size_t *cd_nelmts, unsigned cd_values[], size_t namelen, char name[])
| Returns information about a filter in a pipeline (DEPRECATED).
herr_t | H5Pget_filter_by_id1 (hid_t plist_id, H5Z_filter_t id, unsigned int *flags, size_t *cd_nelmts, unsigned cd_values[], size_t namelen, char name[])
| Returns information about the specified filter.
H5D_layout_t | H5Pget_layout (hid_t plist_id)
| Returns the layout of the raw data for a dataset.
herr_t | H5Pget_virtual_count (hid_t dcpl_id, size_t *count)
| Gets the number of mappings for the virtual dataset.
ssize_t | H5Pget_virtual_dsetname (hid_t dcpl_id, size_t index, char *name, size_t size)
| Gets the name of a source dataset used in the mapping.
ssize_t | H5Pget_virtual_filename (hid_t dcpl_id, size_t index, char *name, size_t size)
| Gets the filename of a source dataset used in the mapping.
herr_t | H5Pget_virtual_spatial_tree (hid_t dcpl_id, bool *use_tree)
| Retrieves the setting for whether or not to use a spatial tree for VDS mappings.
hid_t | H5Pget_virtual_srcspace (hid_t dcpl_id, size_t index)
| Gets a dataspace identifier for the selection within the source dataset used in the mapping.
hid_t | H5Pget_virtual_vspace (hid_t dcpl_id, size_t index)
| Gets a dataspace identifier for the selection within the virtual dataset used in the mapping.
herr_t | H5Pset_alloc_time (hid_t plist_id, H5D_alloc_time_t alloc_time)
| Sets the timing for storage space allocation.
herr_t | H5Pset_chunk (hid_t plist_id, int ndims, const hsize_t dim[])
| Sets the size of the chunks used to store a chunked layout dataset.
herr_t | H5Pset_chunk_opts (hid_t plist_id, unsigned opts)
| Sets the edge chunk option in a dataset creation property list.
herr_t | H5Pset_deflate (hid_t plist_id, unsigned level)
| Sets deflate (GNU gzip) compression method and compression level.
herr_t | H5Pset_dset_no_attrs_hint (hid_t dcpl_id, bool minimize)
| Sets the flag to create minimized dataset object headers.
herr_t | H5Pset_external (hid_t plist_id, const char *name, HDoff_t offset, hsize_t size)
| Adds an external file to the list of external files.
herr_t | H5Pset_fill_time (hid_t plist_id, H5D_fill_time_t fill_time)
| Sets the time when fill values are written to a dataset.
herr_t | H5Pset_fill_value (hid_t plist_id, hid_t type_id, const void *value)
| Sets the fill value for a dataset.
herr_t | H5Pset_layout (hid_t plist_id, H5D_layout_t layout)
| Sets the type of storage used to store the raw data for a dataset.
herr_t | H5Pset_nbit (hid_t plist_id)
| Sets up the use of the N-Bit filter.
herr_t | H5Pset_scaleoffset (hid_t plist_id, H5Z_SO_scale_type_t scale_type, int scale_factor)
| Sets up the use of the scale-offset filter.
herr_t | H5Pset_shuffle (hid_t plist_id)
| Sets up use of the shuffle filter.
herr_t | H5Pset_szip (hid_t plist_id, unsigned options_mask, unsigned pixels_per_block)
| Sets up use of the SZIP compression filter.
herr_t | H5Pset_virtual (hid_t dcpl_id, hid_t vspace_id, const char *src_file_name, const char *src_dset_name, hid_t src_space_id)
| Sets the mapping between virtual and source datasets.
herr_t | H5Pset_virtual_spatial_tree (hid_t dcpl_id, bool use_tree)
| Sets the flag to use a spatial tree for mappings.

## Function Documentation

## ◆ H5Pall_filters_avail()

htri_t H5Pall_filters_avail | ( | hid_t | plist_id | ) |

Verifies that all required filters are available.

Parameters

  [in] | plist_id | Property list identifier

Returns
  Returns zero (false), a positive (true) or a negative (failure) value.

H5Pall_filters_avail() verifies that all of the filters set in the dataset or group creation property list `plist_id` are currently available.

Version
  1.8.5 Function extended to work with group creation property lists.

Since
  1.6.0

## ◆ H5Pfill_value_defined()

herr_t H5Pfill_value_defined | ( | hid_t | plist,
|  | H5D_fill_value_t * | status )

Determines whether fill value is defined.

Parameters

  [in] | plist | Dataset creation property list identifier
  [out] | status | Status of fill value in property list

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pfill_value_defined() determines whether a fill value is defined in the dataset creation property list `plist`. Valid values returned in status are as follows:

H5D_FILL_VALUE_UNDEFINED | Fill value is undefined.
H5D_FILL_VALUE_DEFAULT | Fill value is the library default.
H5D_FILL_VALUE_USER_DEFINED | Fill value is defined by the application.

Since
  1.6.0

## ◆ H5Pget_alloc_time()

herr_t H5Pget_alloc_time | ( | hid_t | plist_id,
|  | H5D_alloc_time_t * | alloc_time )

Retrieves the timing for storage space allocation.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [out] | alloc_time | The timing setting for allocating dataset storage space

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pget_alloc_time() retrieves the timing for allocating storage space for a dataset's raw data. This property is set in the dataset creation property list `plist_id`. The timing setting is returned in `alloc_time` as one of the following values:

H5D_ALLOC_TIME_DEFAULT | Uses the default allocation time, based on the dataset storage method. See the `alloc_time` description in H5Pset_alloc_time() for default allocation times for various storage methods.
H5D_ALLOC_TIME_EARLY | All space is allocated when the dataset is created.
H5D_ALLOC_TIME_INCR | Space is allocated incrementally as data is written to the dataset.
H5D_ALLOC_TIME_LATE | All space is allocated when data is first written to the dataset.

Note
  H5Pget_alloc_time() is designed to work in concert with the dataset fill value and fill value write time properties, set with the functions H5Pget_fill_value() and H5Pget_fill_time().

Since
  1.6.0

## ◆ H5Pget_chunk()

int H5Pget_chunk | ( | hid_t | plist_id,
|  | int | max_ndims,
|  | hsize_t | dim[] )

Retrieves the size of chunks for the raw data of a chunked layout dataset.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | max_ndims | Size of the `dims` array
  [out] | dim | Array to store the chunk dimensions

Returns
  Returns chunk dimensionality if successful; otherwise returns a negative value.

H5Pget_chunk() retrieves the size of chunks for the raw data of a chunked layout dataset. This function is only valid for dataset creation property lists. At most, `max_ndims` elements of `dim` will be initialized.

Since
  1.0.0

## ◆ H5Pget_chunk_opts()

herr_t H5Pget_chunk_opts | ( | hid_t | plist_id,
|  | unsigned * | opts )

Retrieves the edge chunk option setting from a dataset creation property list.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [out] | opts | Edge chunk option flag. Valid values are described in H5Pset_chunk_opts(). The option status can be retrieved using the bitwise AND operator ( & ). For example, the expression (opts&H5D_CHUNK_DONT_FILTER_PARTIAL_CHUNKS) will evaluate to H5D_CHUNK_DONT_FILTER_PARTIAL_CHUNKS if that option has been enabled. Otherwise, it will evaluate to 0 (zero).

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pget_chunk_opts() retrieves the edge chunk option setting stored in the dataset creation property list `plist_id`.

Since
  1.10.0

## ◆ H5Pget_dset_no_attrs_hint()

herr_t H5Pget_dset_no_attrs_hint | ( | hid_t | dcpl_id,
|  | bool * | minimize )

Retrieves the setting for whether or not to create minimized dataset object headers.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [out] | minimize | Flag indicating whether the library will or will not create minimized dataset object headers

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pget_dset_no_attrs_hint() retrieves the no dataset attributes hint setting for the dataset creation property list `dcpl_id`. This setting is used to inform the library to create minimized dataset object headers when true. The setting value is returned in the boolean pointer `minimize`.

Since
  1.10.5

## ◆ H5Pget_external()

herr_t H5Pget_external | ( | hid_t | plist_id,
|  | unsigned | idx,
|  | size_t | name_size,
|  | char * | name,
|  | HDoff_t * | offset,
|  | hsize_t * | size )

Returns information about an external file.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | idx | External file index
  [in] | name_size | Maximum length of `name` array
  [out] | name | Name of the external file
  [out] | offset | Pointer to a location to return an offset value
  [out] | size | Pointer to a location to return the size of the external file data

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pget_external() returns information about an external file. The external file is specified by its index, `idx`, which is a number from zero to N-1, where N is the value returned by H5Pget_external_count(). At most `name_size` characters are copied into the `name` array. If the external file name is longer than `name_size` with the null terminator, the return value is not null terminated (similar to strncpy()).

If `name_size` is zero or `name` is the null pointer, the external file name is not returned. If `offset` or `size` are null pointers then the corresponding information is not returned.

Note
  In 1.14.x and earlier, the offset parameter was of type off_t, which is a 32-bit signed long value on Windows, which limited the valid offset that can be returned to 2 GiB.

Version
  2.0.0 `offset` parameter type changed to HDoff_t from off_t.
  1.6.4 `idx` parameter type changed to unsigned.

Since
  1.0.0

## ◆ H5Pget_external_count()

int H5Pget_external_count | ( | hid_t | plist_id | ) |

Returns the number of external files for a dataset.

Parameters

  [in] | plist_id | Dataset creation property list identifier

Returns
  Returns the number of external files if successful; otherwise returns a negative value.

H5Pget_external_count() returns the number of external files for the specified dataset.

Since
  1.0.0

## ◆ H5Pget_fill_time()

herr_t H5Pget_fill_time | ( | hid_t | plist_id,
|  | H5D_fill_time_t * | fill_time )

Retrieves the time when fill values are written to a dataset.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [out] | fill_time | Setting for the timing of writing fill values to the dataset

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pget_fill_time() examines the dataset creation property list `plist_id` to determine when fill values are to be written to a dataset. Valid values returned in `fill_time` are as follows:

H5D_FILL_TIME_IFSET | Fill values are written to the dataset when storage space is allocated only if there is a user-defined fill value, i.e., one set with H5Pset_fill_value(). (Default)
H5D_FILL_TIME_ALLOC | Fill values are written to the dataset when storage space is allocated.
H5D_FILL_TIME_NEVER | Fill values are never written to the dataset.

Note
  H5Pget_fill_time() is designed to work in coordination with the dataset fill value and dataset storage allocation time properties, retrieved with the functions H5Pget_fill_value() and H5Pget_alloc_time().type == H5FD_MEM_DRAW

Since
  1.6.0

## ◆ H5Pget_fill_value()

herr_t H5Pget_fill_value | ( | hid_t | plist_id,
|  | hid_t | type_id,
|  | void * | value )

Retrieves a dataset fill value.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | type_id | Datatype identifier for the value passed via `value`
  [out] | value | Pointer to buffer to contain the returned fill value

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pget_fill_value() returns the dataset fill value defined in the dataset creation property list `plist_id`. The fill value is returned through the `value` pointer and will be converted to the datatype specified by `type_id`. This datatype may differ from the fill value datatype in the property list, but the HDF5 library must be able to convert between the two datatypes.

If the fill value is undefined, i.e., set to NULL in the property list, H5Pget_fill_value() will return an error. H5Pfill_value_defined() should be used to check for this condition before H5Pget_fill_value() is called.

Memory must be allocated by the calling application.

Note
  H5Pget_fill_value() is designed to coordinate with the dataset storage allocation time and fill value write time properties, which can be retrieved with the functions H5Pget_alloc_time() and H5Pget_fill_time(), respectively.

Since
  1.0.0

## ◆ H5Pget_filter1()

H5Z_filter_t H5Pget_filter1 | ( | hid_t | plist_id,
|  | unsigned | filter,
|  | unsigned int * | flags,
|  | size_t * | cd_nelmts,
|  | unsigned | cd_values[],
|  | size_t | namelen,
|  | char | name[] )

Returns information about a filter in a pipeline (DEPRECATED).

Parameters

  [in] | plist_id | Property list identifier
  [in] | filter | Sequence number within the filter pipeline of the filter for which information is sought
  [out] | flags | Bit vector specifying certain general properties of the filter
  [in,out] | cd_nelmts | Number of elements in `cd_values`
  [out] | cd_values | Auxiliary data for the filter
  [in] | namelen | Anticipated number of characters in `name`
  [out] | name | Name of the filter

Returns
  Returns the filter identifier if successful; Otherwise returns a negative value. See: H5Z_filter_t

Deprecated
  When was this function deprecated?

H5Pget_filter1() returns information about a filter, specified by its filter number, in a filter pipeline, specified by the property list with which it is associated.

`plist_id` must be a dataset or group creation property list.

`filter` is a value between zero and N-1, as described in H5Pget_nfilters(). The function will return a negative value if the filter number is out of range.

The structure of the `flags` argument is discussed in H5Pset_filter().

On input, `cd_nelmts` indicates the number of entries in the `cd_values` array, as allocated by the caller; on return, `cd_nelmts` contains the number of values defined by the filter.

If `name` is a pointer to an array of at least `namelen` bytes, the filter name will be copied into that array. The name will be null terminated if `namelen` is large enough. The filter name returned will be the name appearing in the file, the name registered for the filter, or an empty string.

Version
  1.8.5 Function extended to work with group creation property lists.
  1.8.0 N-bit and scale-offset filters added.
  1.8.0 Function H5Pget_filter() renamed to H5Pget_filter1() and deprecated in this release.
  1.6.4 `filter` parameter type changed to unsigned.

Since
  1.0.0

## ◆ H5Pget_filter_by_id1()

herr_t H5Pget_filter_by_id1 | ( | hid_t | plist_id,
|  | H5Z_filter_t | id,
|  | unsigned int * | flags,
|  | size_t * | cd_nelmts,
|  | unsigned | cd_values[],
|  | size_t | namelen,
|  | char | name[] )

Returns information about the specified filter.

Parameters

  [in] | plist_id | Property list identifier
  [in] | id | Filter identifier
  [out] | flags | Bit vector specifying certain general properties of the filter
  [in,out] | cd_nelmts | Number of elements in `cd_values`
  [out] | cd_values | Auxiliary data for the filter
  [in] | namelen | Anticipated number of characters in `name`
  [out] | name | Name of the filter

Returns
  Returns a non-negative value if successful; Otherwise returns a negative value.

Deprecated
  As of HDF5-1.8 this function was deprecated in favor of H5Pget_filter_by_id2() or the macro H5Pget_filter_by_id().

H5Pget_filter_by_id1() returns information about a filter, specified in `id`, a filter identifier.

`plist_id` must be a dataset or group creation property list and `id` must be in the associated filter pipeline.

The `id` and `flags` parameters are used in the same manner as described in the discussion of H5Pset_filter().

Aside from the fact that they are used for output, the parameters `cd_nelmts` and `cd_values`[] are used in the same manner as described in the discussion of H5Pset_filter(). On input, the `cd_nelmts` parameter indicates the number of entries in the `cd_values`[] array allocated by the calling program; on exit it contains the number of values defined by the filter.

On input, the `namelen` parameter indicates the number of characters allocated for the filter name by the calling program in the array `name`[]. On exit `name`[] contains the name of the filter with one character of the name in each element of the array.

If the filter specified in `id` is not set for the property list, an error will be returned and this function will fail.

Version
  1.8.5 Function extended to work with group creation property lists.
  1.8.0 Function H5Pget_filter_by_id() renamed to H5Pget_filter_by_id1() and deprecated in this release.

Since
  1.6.0

## ◆ H5Pget_layout()

H5D_layout_t H5Pget_layout | ( | hid_t | plist_id | ) |

Returns the layout of the raw data for a dataset.

Parameters

  [in] | plist_id | Dataset creation property list identifier

Returns
  Returns the layout type (a non-negative value) of a dataset creation property list if successful. Valid return values are:
  - H5D_COMPACT: Raw data is stored in the object header in the file.
  - H5D_CONTIGUOUS: Raw data is stored separately from the object header in one contiguous chunk in the file.
  - H5D_CHUNKED: Raw data is stored separately from the object header in chunks in separate locations in the file.
  - H5D_VIRTUAL: Raw data is drawn from multiple datasets in different files.
  Otherwise, returns a negative value indicating failure.

H5Pget_layout() returns the layout of the raw data for a dataset. This function is only valid for dataset creation property lists.

Note that a compact storage layout may affect writing data to the dataset with parallel applications. See the H5Dwrite() documentation for details.

Version
  1.10.0 H5D_VIRTUAL added in this release.

Since
  1.0.0

## ◆ H5Pget_virtual_count()

herr_t H5Pget_virtual_count | ( | hid_t | dcpl_id,
|  | size_t * | count )

Gets the number of mappings for the virtual dataset.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [out] | count | The number of mappings

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pget_virtual_count() gets the number of mappings for a virtual dataset that has the creation property list specified by `dcpl_id`.

See also
  Supporting Functions: H5Pget_layout(), H5Pset_layout(), H5Sget_regular_hyperslab(), H5Sis_regular_hyperslab(), H5Sselect_hyperslab()
  VDS Functions: H5Pget_virtual_count(), H5Pget_virtual_dsetname(), H5Pget_virtual_filename(), H5Pget_virtual_prefix(), H5Pget_virtual_printf_gap(), H5Pget_virtual_srcspace(), H5Pget_virtual_view(), H5Pget_virtual_vspace(), H5Pset_virtual(), H5Pset_virtual_prefix(), H5Pset_virtual_printf_gap(), H5Pset_virtual_view()

Since
  1.10.0

## ◆ H5Pget_virtual_dsetname()

ssize_t H5Pget_virtual_dsetname | ( | hid_t | dcpl_id,
|  | size_t | index,
|  | char * | name,
|  | size_t | size )

Gets the name of a source dataset used in the mapping.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [in] | index | Mapping index. The value of `index` is 0 (zero) or greater and less than `count` (0 ≤ `index` < `count`), where `count` is the number of mappings returned by H5Pget_virtual_count().
  [out] | name | A buffer containing the name of the source dataset
  [in] | size | The size, in bytes, of the `name` buffer. Must be the size of the dataset name in bytes plus 1 for a NULL terminator

Returns
  Returns the length of the dataset name if successful; otherwise returns a negative value.

H5Pget_virtual_dsetname() takes the dataset creation property list for the virtual dataset, `dcpl_id`, the mapping index, `index`, the size of the dataset name for a source dataset, `size`, and retrieves the name of the source dataset used in the mapping.

Up to `size` characters of the dataset name are returned in `name`; additional characters, if any, are not returned to the user application.

Up to `size` characters of the dataset name are returned in `name`; additional characters, if any, are not returned to the user application.
If the length of the dataset name, which determines the required value of `size`, is unknown, a preliminary call to H5Pget_virtual_dsetname() with the last two parameters set to NULL and zero respectively can be made. The return value of this call will be the size in bytes of the dataset name. That value, plus 1 for a NULL terminator, must then be assigned to `size` for a second H5Pget_virtual_dsetname() call, which will retrieve the actual dataset name.

See also
  Supporting Functions: H5Pget_layout(), H5Pset_layout(), H5Sget_regular_hyperslab(), H5Sis_regular_hyperslab(), H5Sselect_hyperslab()
  VDS Functions: H5Pget_virtual_count(), H5Pget_virtual_dsetname(), H5Pget_virtual_filename(), H5Pget_virtual_prefix(), H5Pget_virtual_printf_gap(), H5Pget_virtual_srcspace(), H5Pget_virtual_view(), H5Pget_virtual_vspace(), H5Pset_virtual(), H5Pset_virtual_prefix(), H5Pset_virtual_printf_gap(), H5Pset_virtual_view()

Since
  1.10.0

## ◆ H5Pget_virtual_filename()

ssize_t H5Pget_virtual_filename | ( | hid_t | dcpl_id,
|  | size_t | index,
|  | char * | name,
|  | size_t | size )

Gets the filename of a source dataset used in the mapping.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [in] | index | Mapping index. The value of `index` is 0 (zero) or greater and less than `count` (0 ≤ `index` < `count`), where `count` is the number of mappings returned by H5Pget_virtual_count().
  [out] | name | A buffer containing the name of the file containing the source dataset
  [in] | size | The size, in bytes, of the name buffer. Must be the size of the filename in bytes plus 1 for a NULL terminator

Returns
  Returns the length of the filename if successful; otherwise returns a negative value.

H5Pget_virtual_filename() takes the dataset creation property list for the virtual dataset, `dcpl_id`, the mapping index, `index`, the size of the filename for a source dataset, `size`, and retrieves the name of the file for a source dataset used in the mapping.

Up to `size` characters of the filename are returned in `name`; additional characters, if any, are not returned to the user application.

Up to `size` characters of the file name are returned in `name`; additional characters, if any, are not returned to the user application.
If the length of the file name, which determines the required value of `size`, is unknown, a preliminary call to H5Pget_virtual_filename() with the last two parameters set to NULL and zero respectively can be made. The return value of this call will be the size in bytes of the file name. That value, plus 1 for a NULL terminator, must then be assigned to `size` for a second H5Pget_virtual_filename() call, which will retrieve the actual file name.

See also
  Supporting Functions: H5Pget_layout(), H5Pset_layout(), H5Sget_regular_hyperslab(), H5Sis_regular_hyperslab(), H5Sselect_hyperslab()
  VDS Functions: H5Pget_virtual_count(), H5Pget_virtual_dsetname(), H5Pget_virtual_filename(), H5Pget_virtual_prefix(), H5Pget_virtual_printf_gap(), H5Pget_virtual_srcspace(), H5Pget_virtual_view(), H5Pget_virtual_vspace(), H5Pset_virtual(), H5Pset_virtual_prefix(), H5Pset_virtual_printf_gap(), H5Pset_virtual_view()

Since
  1.10.0

## ◆ H5Pget_virtual_spatial_tree()

herr_t H5Pget_virtual_spatial_tree | ( | hid_t | dcpl_id,
|  | bool * | use_tree )

Retrieves the setting for whether or not to use a spatial tree for VDS mappings.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [out] | use_tree | Flag indicating whether the dataset will or will not use a spatial tree

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pget_virtual_spatial_tree() retrieves the use spatial tree flag setting for the dataset creation property list `dcpl_id`. This setting determines whether a dataset created with the dataset creation property list `dcpl_id` will construct a spatial tree and use it in an attempt to optimize certain operations. The setting value is returned in the boolean pointer `use_tree`.

Use of a spatial tree will accelerate the process of searching through mappings to determine which contain intersections with the user's selection region. With the tree disabled, all mappings will simply be iterated through and checked directly.

Certain workflows may find that tree creation overhead outweighs the time saved on reads. In this case, disabling this property will lead to a performance improvement, though it is expected that almost all cases will benefit from the tree on net.

Since
  2.0.0

## ◆ H5Pget_virtual_srcspace()

hid_t H5Pget_virtual_srcspace | ( | hid_t | dcpl_id,
|  | size_t | index )

Gets a dataspace identifier for the selection within the source dataset used in the mapping.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [in] | index | Mapping index. The value of `index` is 0 (zero) or greater and less than `count` (0 ≤ `index` < `count`), where `count` is the number of mappings returned by H5Pget_virtual_count().

Returns
  Returns a valid dataspace identifier identifier if successful; otherwise returns H5I_INVALID_HID.

H5Pget_virtual_srcspace() takes the dataset creation property list for the virtual dataset, `dcpl_id`, and the mapping index, `index`, and returns a dataspace identifier for the selection within the source dataset used in the mapping.

See also
  Supporting Functions: H5Pget_layout(), H5Pset_layout(), H5Sget_regular_hyperslab(), H5Sis_regular_hyperslab(), H5Sselect_hyperslab()
  VDS Functions: H5Pget_virtual_count(), H5Pget_virtual_dsetname(), H5Pget_virtual_filename(), H5Pget_virtual_prefix(), H5Pget_virtual_printf_gap(), H5Pget_virtual_srcspace(), H5Pget_virtual_view(), H5Pget_virtual_vspace(), H5Pset_virtual(), H5Pset_virtual_prefix(), H5Pset_virtual_printf_gap(), H5Pset_virtual_view()

Since
  1.10.0

## ◆ H5Pget_virtual_vspace()

hid_t H5Pget_virtual_vspace | ( | hid_t | dcpl_id,
|  | size_t | index )

Gets a dataspace identifier for the selection within the virtual dataset used in the mapping.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [in] | index | Mapping index. The value of `index` is 0 (zero) or greater and less than `count` (0 ≤ `index` < `count`), where `count` is the number of mappings returned by H5Pget_virtual_count()

Returns
  Returns a valid dataspace identifier identifier if successful; otherwise returns H5I_INVALID_HID.

H5Pget_virtual_vspace() takes the dataset creation property list for the virtual dataset, `dcpl_id`, and the mapping index, `index`, and returns a dataspace identifier for the selection within the virtual dataset used in the mapping.

See also
  Supporting Functions: H5Pget_layout(), H5Pset_layout(), H5Sget_regular_hyperslab(), H5Sis_regular_hyperslab(), H5Sselect_hyperslab()
  VDS Functions: H5Pget_virtual_count(), H5Pget_virtual_dsetname(), H5Pget_virtual_filename(), H5Pget_virtual_prefix(), H5Pget_virtual_printf_gap(), H5Pget_virtual_srcspace(), H5Pget_virtual_view(), H5Pget_virtual_vspace(), H5Pset_virtual(), H5Pset_virtual_prefix(), H5Pset_virtual_printf_gap(), H5Pset_virtual_view()

Since
  1.10.0

## ◆ H5Pset_alloc_time()

herr_t H5Pset_alloc_time | ( | hid_t | plist_id,
|  | H5D_alloc_time_t | alloc_time )

Sets the timing for storage space allocation.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | alloc_time | When to allocate dataset storage space

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_alloc_time() sets up the timing for the allocation of storage space for a dataset's raw data. This property is set in the dataset creation property list `plist_id`. Timing is specified in `alloc_time` with one of the following values:

H5D_ALLOC_TIME_DEFAULT | Allocate dataset storage space at the default time (Defaults differ by storage method.)
H5D_ALLOC_TIME_EARLY | Allocate all space when the dataset is created (Default for compact datasets.)
H5D_ALLOC_TIME_INCR | Allocate space incrementally, as data is written to the dataset (Default for chunked storage datasets.) Chunked datasets: Storage space allocation for each chunk is deferred until data is written to the chunk. Contiguous datasets: Incremental storage space allocation for contiguous data is treated as late allocation. Compact datasets: Incremental allocation is not allowed with compact datasets; H5Pset_alloc_time() will return an error.
H5D_ALLOC_TIME_LATE | Allocate all space when data is first written to the dataset (Default for contiguous datasets.)

Note
  H5Pset_alloc_time() is designed to work in concert with the dataset fill value and fill value write time properties, set with the functions H5Pset_fill_value() and H5Pset_fill_time().
  See H5Dcreate() for further cross-references.

Since
  1.6.0

## ◆ H5Pset_chunk()

herr_t H5Pset_chunk | ( | hid_t | plist_id,
|  | int | ndims,
|  | const hsize_t | dim[] )

Sets the size of the chunks used to store a chunked layout dataset.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | ndims | The number of dimensions of each chunk
  [in] | dim | An array defining the size, in dataset elements, of each chunk

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_chunk() sets the size of the chunks used to store a chunked layout dataset. This function is only valid for dataset creation property lists.

The `ndims` parameter currently must be the same size as the rank of the dataset.

The values of the `dim` array define the size of the chunks to store the dataset's raw data. The unit of measure for `dim` values is dataset elements.

As a side-effect of this function, the layout of the dataset is changed to H5D_CHUNKED, if it is not already so set.

Note
  Chunk size cannot exceed the size of a fixed-size dataset. For example, a dataset consisting of a 5x4 fixed-size array cannot be defined with 10x10 chunks.
  With HDF5 version 2.0.0, creation of datasets with chunks larger than 4 GiB is now supported. However, doing so will upgrade the file format and prevent earlier versions of the library from being able to open the dataset. Users must also be aware that some operations will require the entire chunk be brought into memory, such as when there is a fill value or data filter set. These operations will not work on 32 bit systems when using chunks with size >= 4 GiB. The file format will be upgraded when the size of an unfiltered chunk is greater than 232-1 which is equal to 4,294,967,295. If a filter grows a chunk from below this value to above it, the write may fail since the file format was not automatically upgraded. To fix this, users can call H5Pset_libver_bounds() with H5F_LIBVER_V200 as the low bound. With the new file format, chunk sizes are now limited to 264-1.

See also
  H5Pset_layout(), H5Dwrite()

Since
  1.0.0

## ◆ H5Pset_chunk_opts()

herr_t H5Pset_chunk_opts | ( | hid_t | plist_id,
|  | unsigned | opts )

Sets the edge chunk option in a dataset creation property list.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | opts | Edge chunk option flag. Valid values are: H5D_CHUNK_DONT_FILTER_PARTIAL_CHUNKS When enabled, filters are not applied to partial edge chunks. When disabled, partial edge chunks are filtered. Enabling this option will improve performance when appending to the dataset and, when compression filters are used, prevent reallocation of these chunks. Datasets created with this option enabled will be inaccessible with HDF5 library versions before Release 1.10. Default: Disabled 0 (zero) Disables option; partial edge chunks will be compressed.

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_chunk_opts() sets the edge chunk option in the dataset creation property list `dcpl_id`.

The available option is detailed in the parameters section. Only chunks that are not completely filled by the dataset's dataspace are affected by this option. Such chunks are referred to as partial edge chunks.

Motivation: H5Pset_chunk_opts() is used to specify storage options for chunks on the edge of a dataset's dataspace. This capability allows the user to tune performance in cases where the dataset size may not be a multiple of the chunk size and the handling of partial edge chunks can impact performance.

Since
  1.10.0

## ◆ H5Pset_deflate()

herr_t H5Pset_deflate | ( | hid_t | plist_id,
|  | unsigned | level )

Sets deflate (GNU gzip) compression method and compression level.

Parameters

  [in] | plist_id | Object creation property list identifier
  [in] | level | Compression level

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

Attention
  If you are planning to use compression with parallel HDF5, ensure that calls to H5Dwrite() occur in collective mode. In other words, all MPI ranks (in the relevant communicator) call H5Dwrite() and pass a dataset transfer property list with the MPI-IO collective option property set to H5FD_MPIO_COLLECTIVE_IO.
  Note that data transformations are currently not supported when writing to datasets in parallel and with compression enabled.

H5Pset_deflate() sets the deflate compression method and the compression level, `level`, for a dataset or group creation property list, `plist_id`.

The filter identifier set in the property list is H5Z_FILTER_DEFLATE.

The compression level, `level`, is a value from zero to nine, inclusive. A compression level of 0 (zero) indicates no compression; compression improves but speed slows progressively from levels 1 through 9:

Compression Level | Gzip Action
--- | ---
0 | No compression
1 | Best compression speed; least compression
2 through 8 | Compression improves; speed degrades
9 | Best compression ratio; slowest speed

Note that setting the compression level to 0 (zero) does not turn off use of the gzip filter; it simply sets the filter to perform no compression as it processes the data.

HDF5 relies on GNU gzip for this compression.

Version
  1.8.5 Function extended to work with group creation property lists.

Since
  1.0.0

## ◆ H5Pset_dset_no_attrs_hint()

herr_t H5Pset_dset_no_attrs_hint | ( | hid_t | dcpl_id,
|  | bool | minimize )

Sets the flag to create minimized dataset object headers.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [in] | minimize | Flag for indicating whether or not a dataset's object header will be minimized

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_dset_no_attrs_hint() sets the no dataset attributes hint setting for the dataset creation property list `dcpl_id`. Datasets created with the dataset creation property list `dcpl_id` will have their object headers minimized if the boolean flag `minimize` is set to true. By setting `minimize` to true, the library expects that no attributes will be added to the dataset. Attributes can be added, but they are appended with a continuation message, which can reduce performance.

This setting interacts with H5Fset_dset_no_attrs_hint(): if either is set to true, then the created dataset's object header will be minimized.

Since
  1.10.5

## ◆ H5Pset_external()

herr_t H5Pset_external | ( | hid_t | plist_id,
|  | const char * | name,
|  | HDoff_t | offset,
|  | hsize_t | size )

Adds an external file to the list of external files.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | name | Name of an external file
  [in] | offset | Offset, in bytes, from the beginning of the file to the location in the file where the data starts
  [in] | size | Number of bytes reserved in the file for the data

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

The first call to H5Pset_external() sets the external storage property in the property list, thus designating that the dataset will be stored in one or more non-HDF5 file(s) external to the HDF5 file. This call also adds the file `name` as the first file in the list of external files. Subsequent calls to the function add the named file as the next file in the list.

If a dataset is split across multiple files, then the files should be defined in order. The total size of the dataset is the sum of the `size` arguments for all the external files. If the total size is larger than the size of a dataset then the dataset can be extended (provided the data space also allows the extending).

The `size` argument specifies the number of bytes reserved for data in the external file. If `size` is set to H5F_UNLIMITED, the external file can be of unlimited size and no more files can be added to the external files list. If `size` is set to 0 (zero), no external file will actually be created.

All of the external files for a given dataset must be specified with H5Pset_external() before H5Dcreate() is called to create the dataset. If one these files does not exist on the system when H5Dwrite() is called to write data to it, the library will create the file.

Note
  In 1.14.x and earlier, the offset parameter was of type off_t, which is a 32-bit signed long value on Windows, which limited the valid offset that can be set to 2 GiB.

Version
  2.0.0 `offset` parameter type changed to HDoff_t from off_t.

Since
  1.0.0

## ◆ H5Pset_fill_time()

herr_t H5Pset_fill_time | ( | hid_t | plist_id,
|  | H5D_fill_time_t | fill_time )

Sets the time when fill values are written to a dataset.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | fill_time | When to write fill values to a dataset

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_fill_time() sets up the timing for writing fill values to a dataset. This property is set in the dataset creation property list `plist_id`. Timing is specified in `fill_time` with one of the following values:

H5D_FILL_TIME_IFSET | Write fill values to the dataset when storage space is allocated only if there is a user-defined fill value, i.e.,one set with H5Pset_fill_value(). (Default)
H5D_FILL_TIME_ALLOC | Write fill values to the dataset when storage space is allocated.
H5D_FILL_TIME_NEVER | Never write fill values to the dataset.

Note
  H5Pset_fill_time() is designed for coordination with the dataset fill value and dataset storage allocation time properties, set with the functions H5Pset_fill_value() and H5Pset_alloc_time(). See H5Dcreate() for further cross-references.

Since
  1.6.0

## ◆ H5Pset_fill_value()

herr_t H5Pset_fill_value | ( | hid_t | plist_id,
|  | hid_t | type_id,
|  | const void * | value )

Sets the fill value for a dataset.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | type_id | Datatype of `value`
  [in] | value | Pointer to buffer containing value to use as fill value

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_fill_value() sets the fill value for a dataset in the dataset creation property list. `value` is interpreted as being of datatype `type_id`. This datatype may differ from that of the dataset, but the HDF5 library must be able to convert `value` to the dataset datatype when the dataset is created.

The default fill value is 0 (zero), which is interpreted according to the actual dataset datatype.

Setting `value` to NULL indicates that the fill value is to be undefined.

Note
  Applications sometimes write data only to portions of an allocated dataset. It is often useful in such cases to fill the unused space with a known fill value. This function allows the user application to set that fill value; the functions H5Dfill() and H5Pset_fill_time(), respectively, provide the ability to apply the fill value on demand or to set up its automatic application.
  A fill value should be defined so that it is appropriate for the application. While the HDF5 default fill value is 0 (zero), it is often appropriate to use another value. It might be useful, for example, to use a value that is known to be impossible for the application to legitimately generate.
  H5Pset_fill_value() is designed to work in concert with H5Pset_alloc_time() and H5Pset_fill_time(). H5Pset_alloc_time() and H5Pset_fill_time() govern the timing of dataset storage allocation and fill value write operations and can be important in tuning application performance.
  See H5Dcreate() for further cross-references.

Since
  1.0.0

## ◆ H5Pset_layout()

herr_t H5Pset_layout | ( | hid_t | plist_id,
|  | H5D_layout_t | layout )

Sets the type of storage used to store the raw data for a dataset.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | layout | Type of storage layout for raw data

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_layout() sets the type of storage used to store the raw data for a dataset. This function is only valid for dataset creation property lists.

Valid values for `layout` are:

- H5D_COMPACT: Store raw data in the dataset object header in file. This should only be used for datasets with small amounts of raw data. The raw data size limit is 64K (65520 bytes). Attempting to create a dataset with raw data larger than this limit will cause the H5Dcreate() call to fail.
- H5D_CONTIGUOUS: Store raw data separately from the object header in one large chunk in the file.
- H5D_CHUNKED: Store raw data separately from the object header as chunks of data in separate locations in the file.
- H5D_VIRTUAL: Draw raw data from multiple datasets in different files.

Note that a compact storage layout may affect writing data to the dataset with parallel applications. See the note in H5Dwrite() documentation for details.

Version
  1.10.0 H5D_VIRTUAL added in this release.

Since
  1.0.0

## ◆ H5Pset_nbit()

herr_t H5Pset_nbit | ( | hid_t | plist_id | ) |

Sets up the use of the N-Bit filter.

Parameters

  [in] | plist_id | Dataset creation property list identifier

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

Attention
  If you are planning to use compression with parallel HDF5, ensure that calls to H5Dwrite() occur in collective mode. In other words, all MPI ranks (in the relevant communicator) call H5Dwrite() and pass a dataset transfer property list with the MPI-IO collective option property set to H5FD_MPIO_COLLECTIVE_IO.
  Note that data transformations are currently not supported when writing to datasets in parallel and with compression enabled.

H5Pset_nbit() sets the N-Bit filter, H5Z_FILTER_NBIT, in the dataset creation property list `plist_id`.

The HDF5 user can create an N-Bit datatype with the following code:

             hid_t nbit_datatype = H5Tcopy(H5T_STD_I32LE);
             H5Tset_precision(nbit_datatype, 16);
             H5Tset_offset(nbit_datatype, 4);

In memory, one value of the N-Bit datatype in the above example will be stored on a little-endian machine as follows:

byte 3 | byte 2 | byte 1 | byte 0
???????? | ????SPPP | PPPPPPPP | PPPP????

Note: S - sign bit, P - significant bit, ? - padding bit; For signed integer, the sign bit is included in the precision.

When data of the above datatype is stored on disk using the N-bit filter, all padding bits are chopped off and only significant bits are stored. The values on disk will be something like:

1st value | 2nd value | ...
SPPPPPPPPPPPPPPP | SPPPPPPPPPPPPPPP | ...

The N-Bit filter is used effectively for compressing data of an N-Bit datatype as well as a compound and an array datatype with N-Bit fields. However, the datatype classes of the N-Bit datatype or the N-Bit field of the compound datatype or the array datatype are limited to integer or floating-point.

The N-Bit filter supports complex situations where a compound datatype contains member(s) of a compound datatype or an array datatype that has a compound datatype as the base type. However, it does not support the situation where an array datatype has a variable-length or variable-length string as its base datatype. The filter does support the situation where a variable-length or variable-length string is a member of a compound datatype.

The N-Bit filter allows all other HDF5 datatypes (such as time, string, bitfield, opaque, reference, enum, and variable length) to pass through as a no-op.

Like other I/O filters supported by the HDF5 library, application using the N-Bit filter must store data with chunked storage.

By nature, the N-Bit filter should not be used together with other I/O filters.

Version
  1.8.8 Fortran subroutine introduced in this release.

Since
  1.8.0

## ◆ H5Pset_scaleoffset()

herr_t H5Pset_scaleoffset | ( | hid_t | plist_id,
|  | H5Z_SO_scale_type_t | scale_type,
|  | int | scale_factor )

Sets up the use of the scale-offset filter.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | scale_type | Flag indicating compression method
  [in] | scale_factor | Parameter related to scale. Must be non-negative

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

Attention
  If you are planning to use compression with parallel HDF5, ensure that calls to H5Dwrite() occur in collective mode. In other words, all MPI ranks (in the relevant communicator) call H5Dwrite() and pass a dataset transfer property list with the MPI-IO collective option property set to H5FD_MPIO_COLLECTIVE_IO.
  Note that data transformations are currently not supported when writing to datasets in parallel and with compression enabled.

H5Pset_scaleoffset() sets the scale-offset filter, H5Z_FILTER_SCALEOFFSET, for a dataset.

Generally speaking, scale-offset compression performs a scale and/or offset operation on each data value and truncates the resulting value to a minimum number of bits (MinBits) before storing it. The current scale-offset filter supports integer and floating-point datatypes.

For an integer datatype, the parameter `scale_type` should be set to H5Z_SO_INT (2). The parameter `scale_factor` denotes MinBits. If the user sets it to H5Z_SO_INT_MINBITS_DEFAULT (0), the filter will calculate MinBits. If `scale_factor` is set to a positive integer, the filter does not do any calculation and just uses the number as MinBits. However, if the user gives a MinBits that is less than what would be generated by the filter, the compression will be lossy. Also, the MinBits supplied by the user cannot exceed the number of bits to store one value of the dataset datatype.

For a floating-point datatype, the filter adopts the GRiB data packing mechanism, which offers two alternate methods: E-scaling and D-scaling. Both methods are lossy compression. If the parameter `scale_type` is set to H5Z_SO_FLOAT_DSCALE (0), the filter will use the D-scaling method; if it is set to H5Z_SO_FLOAT_ESCALE (1), the filter will use the E-scaling method. Since only the D-scaling method is implemented, `scale_type` should be set to H5Z_SO_FLOAT_DSCALE or 0.

When the D-scaling method is used, the original data is "D" scaled — multiplied by 10 to the power of `scale_factor`, and the "significant" part of the value is moved to the left of the decimal point. Care should be taken in setting the decimal `scale_factor` so that the integer part will have enough precision to contain the appropriate information of the data value. For example, if `scale_factor` is set to 2, the number 104.561 will be 10456.1 after "D" scaling. The last digit 1 is not "significant" and is thrown off in the process of rounding. The user should make sure that after "D" scaling and rounding, the data values are within the range that can be represented by the integer (same size as the floating-point type).

Valid values for scale_type are as follows:

H5Z_SO_FLOAT_DSCALE (0) | Floating-point type, using variable MinBits method
H5Z_SO_FLOAT_ESCALE (1) | Floating-point type, using fixed MinBits method
H5Z_SO_INT (2) | Integer type

The meaning of `scale_factor` varies according to the value assigned to `scale_type:`

`scale_type` value | `scale_factor` description
--- | ---
H5Z_SO_FLOAT_DSCALE | Denotes the decimal scale factor for D-scaling and can be positive, negative or zero. This is the current implementation of the library.
H5Z_SO_FLOAT_ESCALE | Denotes MinBits for E-scaling and must be a positive integer. This is not currently implemented by the library.
H5Z_SO_INT | Denotes MinBits and it should be a positive integer or H5Z_SO_INT_MINBITS_DEFAULT (0). If it is less than 0, the library will reset it to 0 since it is not implemented.

Like other I/O filters supported by the HDF5 library, an application using the scale-offset filter must store data with chunked storage.

Version
  1.8.8 Fortran90 subroutine introduced in this release.

Since
  1.8.0

## ◆ H5Pset_shuffle()

herr_t H5Pset_shuffle | ( | hid_t | plist_id | ) |

Sets up use of the shuffle filter.

Parameters

  [in] | plist_id | Dataset creation property list identifier

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

Attention
  If you are planning to use compression with parallel HDF5, ensure that calls to H5Dwrite() occur in collective mode. In other words, all MPI ranks (in the relevant communicator) call H5Dwrite() and pass a dataset transfer property list with the MPI-IO collective option property set to H5FD_MPIO_COLLECTIVE_IO.
  Note that data transformations are currently not supported when writing to datasets in parallel and with compression enabled.

H5Pset_shuffle() sets the shuffle filter, H5Z_FILTER_SHUFFLE, in the dataset creation property list `plist_id`. The shuffle filter de-interlaces a block of data by reordering the bytes. All the bytes from one consistent byte position of each data element are placed together in one block; all bytes from a second consistent byte position of each data element are placed together a second block; etc. For example, given three data elements of a 4-byte datatype stored as 012301230123, shuffling will re-order data as 000111222333. This can be a valuable step in an effective compression algorithm because the bytes in each byte position are often closely related to each other and putting them together can increase the compression ratio.

As implied above, the primary value of the shuffle filter lies in its coordinated use with a compression filter; it does not provide data compression when used alone. When the shuffle filter is applied to a dataset immediately prior to the use of a compression filter, the compression ratio achieved is often superior to that achieved by the use of a compression filter without the shuffle filter.

Since
  1.6.0

## ◆ H5Pset_szip()

herr_t H5Pset_szip | ( | hid_t | plist_id,
|  | unsigned | options_mask,
|  | unsigned | pixels_per_block )

Sets up use of the SZIP compression filter.

Parameters

  [in] | plist_id | Dataset creation property list identifier
  [in] | options_mask | A bit-mask conveying the desired SZIP options; Valid values are H5_SZIP_EC_OPTION_MASK and H5_SZIP_NN_OPTION_MASK.
  [in] | pixels_per_block | The number of pixels or data elements in each data block (max H5_SZIP_MAX_PIXELS_PER_BLOCK)

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

Attention
  If you are planning to use compression with parallel HDF5, ensure that calls to H5Dwrite() occur in collective mode. In other words, all MPI ranks (in the relevant communicator) call H5Dwrite() and pass a dataset transfer property list with the MPI-IO collective option property set to H5FD_MPIO_COLLECTIVE_IO.
  Note that data transformations are currently not supported when writing to datasets in parallel and with compression enabled.

H5Pset_szip() sets an SZIP compression filter, H5Z_FILTER_SZIP, for a dataset. SZIP is a compression method designed for use with scientific data.

Before proceeding, all users should review the “Limitations” section below.

Users familiar with SZIP outside the HDF5 context may benefit from reviewing the Note “For Users Familiar with SZIP in Other Contexts” below.

In the text below, the term pixel refers to an HDF5 data element. This terminology derives from SZIP compression's use with image data, where pixel referred to an image pixel.

The SZIP `bits_per_pixel` value (see Note, below) is automatically set, based on the HDF5 datatype. SZIP can be used with atomic datatypes that may have size of 8, 16, 32, or 64 bits. Specifically, a dataset with a datatype that is 8-, 16-, 32-, or 64-bit signed or unsigned integer; char; or 32- or 64-bit float can be compressed with SZIP. See Note, below, for further discussion of the SZIP `bits_per_pixel` setting.

SZIP options are passed in an options mask, `options_mask`, as follows.

Option | Description (Mutually exclusive; select one)
--- | ---
H5_SZIP_EC_OPTION_MASK | Selects entropy coding method
H5_SZIP_NN_OPTION_MASK | Selects nearest neighbor preprocessing followed by entropy coding

The following guidelines can be used in determining which option to select:

- The entropy coding method, the EC option specified by H5_SZIP_EC_OPTION_MASK, is best suited for data that has been processed. The EC method works best for small numbers.
- The nearest neighbor coding method, the NN option specified by H5_SZIP_NN_OPTION_MASK, preprocesses the data then the applies EC method as above.

Other factors may affect results, but the above criteria provides a good starting point for optimizing data compression.

SZIP compresses data block by block, with a user-tunable block size. This block size is passed in the parameter `pixels_per_block` and must be even and not greater than 32, with typical values being 8, 10, 16, or 32. This parameter affects compression ratio; the more pixel values vary, the smaller this number should be to achieve better performance.

In HDF5, compression can be applied only to chunked datasets. If `pixels_per_block` is bigger than the total number of elements in a dataset chunk, H5Pset_szip() will succeed but the subsequent call to H5Dcreate() will fail; the conflict can be detected only when the property list is used.

To achieve optimal performance for SZIP compression, it is recommended that a chunk's fastest-changing dimension be equal to N times `pixels_per_block` where N is the maximum number of blocks per scan line allowed by the SZIP library. In the current version of SZIP, N is set to 128.

SZIP compression is an optional HDF5 filter.

Limitations:

- SZIP compression cannot be applied to compound, array, variable-length, enumeration, or any other user-defined datatypes. If an SZIP filter is set in a dataset creation property list used to create a dataset containing a non-allowed datatype, the call to H5Dcreate() will fail; the conflict can be detected only when the property list is used.
- Users should be aware that there are factors that affect one's rights and ability to use SZIP compression by reviewing the SZIP copyright notice. (This limitation does not apply to the libaec library).

Note
  For Users Familiar with SZIP in Other Contexts:
  The following notes are of interest primarily to those who have used SZIP compression outside of the HDF5 context. In non-HDF5 applications, SZIP typically requires that the user application supply additional parameters:
  - `pixels_in_object`, the number of pixels in the object to be compressed
  - `bits_per_pixel`, the number of bits per pixel
  - `pixels_per_scanline`, the number of pixels per scan line
  These values need not be independently supplied in the HDF5 environment as they are derived from the datatype and dataspace, which are already known. In particular, HDF5 sets `pixels_in_object` to the number of elements in a chunk and `bits_per_pixel` to the size of the element or pixel datatype.
  The following algorithm is used to set `pixels_per_scanline:`
  - If the size of a chunk's fastest-changing dimension, size, is greater than 4K, set `pixels_per_scanline` to 128 times `pixels_per_block`.
  - If size is less than 4K but greater than `pixels_per_block`, set `pixels_per_scanline` to the minimum of size and 128 times `pixels_per_block`.
  - If size is less than `pixels_per_block` but greater than the number elements in the chunk, set `pixels_per_scanline` to the minimum of the number elements in the chunk and 128 times `pixels_per_block`.
  The HDF5 datatype may have precision that is less than the full size of the data element, e.g., an 11-bit integer can be defined using H5Tset_precision(). To a certain extent, SZIP can take advantage of the precision of the datatype to improve compression:
  - If the HDF5 datatype size is 24-bit or less and the offset of the bits in the HDF5 datatype is zero (see H5Tset_offset() or H5Tget_offset()), the data is the in lowest N bits of the data element. In this case, the SZIP `bits_per_pixel` is set to the precision of the HDF5 datatype.
  - If the offset is not zero, the SZIP `bits_per_pixel` will be set to the number of bits in the full size of the data element.
  - If the HDF5 datatype precision is 25-bit to 32-bit, the SZIP `bits_per_pixel` will be set to 32.
  - If the HDF5 datatype precision is 33-bit to 64-bit, the SZIP `bits_per_pixel` will be set to 64.
  HDF5 always modifies the options mask provided by the user to set up usage of RAW_OPTION_MASK, ALLOW_K13_OPTION_MASK, and one of LSB_OPTION_MASK or MSB_OPTION_MASK, depending on endianness of the datatype.

Since
  1.6.0

## ◆ H5Pset_virtual()

herr_t H5Pset_virtual | ( | hid_t | dcpl_id,
|  | hid_t | vspace_id,
|  | const char * | src_file_name,
|  | const char * | src_dset_name,
|  | hid_t | src_space_id )

Sets the mapping between virtual and source datasets.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [in] | vspace_id | The dataspace identifier with the selection within the virtual dataset applied, possibly an unlimited selection
  [in] | src_file_name | The name of the HDF5 file where the source dataset is located or a . (period) for a source dataset in the same file. The file might not exist yet. The name can be specified using a C-style `printf` statement as described below.
  [in] | src_dset_name | The path to the HDF5 dataset in the file specified by `src_file_name`. The dataset might not exist yet. The dataset name can be specified using a C-style `printf` statement as described below.
  [in] | src_space_id | The source dataset's dataspace identifier with a selection applied, possibly an unlimited selection

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_virtual() maps elements of the virtual dataset (VDS) described by the virtual dataspace identifier `vspace_id` to the elements of the source dataset described by the source dataset dataspace identifier `src_space_id`. The source dataset is identified by the name of the file where it is located, `src_file_name`, and the name of the dataset, `src_dset_name`.

C-style `printf` Formatting Statements:
  C-style `printf` formatting allows a pattern to be specified in the name of a source file or dataset. Strings for the file and dataset names are treated as literals except for the following substitutions:

  %% | Replaced with a single % (percent) character.
  `%<d>b` | Where `<d>` is the virtual dataset dimension axis (0-based) and b indicates that the block count of the selection in that dimension should be used. The full expression (for example, %0b) is replaced with a single numeric value when the mapping is evaluated at VDS access time. Example code for many source and virtual dataset mappings is available in the "Examples of Source to Virtual Dataset Mapping" chapter in the RFC: HDF5 Virtual Dataset.

  If the printf form is used for the source file or dataset names, the selection in the source dataset's dataspace must be fixed-size.

If the family driver is used for the source files of a `printf` mapping, special care must be taken. In this case the VDS code expands the file name with `snprintf` first, then the family driver second. This means that, while the format specifier for the VDS block number is inserted normally, the format specifier for the family file driver member number must be escaped such that it is only recognized as a format specifier the second time it is run through `snprintf`. As an example one may use %%06d as the member file number format specifier in the source file name.

Source File Resolutions:
  When a source dataset residing in a different file is accessed, the library will search for the source file `src_file_name` as described below:
  - If `src_file_name` is a . (period) then it refers to the file containing the virtual dataset.
  - If `src_file_name` is a relative pathname, the following steps are performed:
    - The library will get the prefix(es) set in the environment variable `HDF5_VDS_PREFIX` and will try to prepend each prefix to `src_file_name` to form a new `src_file_name`. If the new `src_file_name` does not exist or if `HDF5_VDS_PREFIX` is not set, the library will get the prefix set via H5Pset_virtual_prefix() and prepend it to `src_file_name` to form a new `src_file_name`. If the new `src_file_name` does not exist or no prefix is being set by H5Pset_virtual_prefix() then the path of the file containing the virtual dataset is obtained. This path can be the absolute path or the current working directory plus the relative path of that file when it is created/opened. The library will prepend this path to `src_file_name` to form a new `src_file_name`.
    - If the new `src_file_name` does not exist, then the library will look for `src_file_name` and will return failure/success accordingly.
  - If `src_file_name` is an absolute pathname, the library will first try to find `src_file_name`. If `src_file_name` does not exist, `src_file_name` is stripped of directory paths to form a new `src_file_name`. The search for the new `src_file_name` then follows the same steps as described above for a relative pathname. See examples below illustrating how `src_file_name` is stripped to form a new `src_file_name`.

  Note that `src_file_name` is considered to be an absolute pathname when the following condition is true:
  - For Unix, the first character of `src_file_name` is a slash (/).
    For example, consider a `src_file_name` of /tmp/A.h5. If that source file does not exist, the new `src_file_name` after stripping will be A.h5.
  - For Windows, there are 6 cases:
    1. `src_file_name` is an absolute drive with absolute pathname.
       For example, consider a `src_file_name` of /tmp/A.h5. If that source file does not exist, the new `src_file_name` after stripping will be A.h5.
    2. `src_file_name` is an absolute pathname without specifying drive name.
       For example, consider a `src_file_name` of /tmp/A.h5. If that source file does not exist, the new `src_file_name` after stripping will be A.h5.
    3. `src_file_name` is an absolute drive with relative pathname.
       For example, consider a `src_file_name` of /tmp/A.h5. If that source file does not exist, the new `src_file_name` after stripping will be tmp/A.h5.
    4. `src_file_name` is in UNC (Uniform Naming Convention) format with server name, share name, and pathname.
       For example, consider a `src_file_name` of /tmp/A.h5. If that source file does not exist, the new `src_file_name` after stripping will be A.h5.
    5. `src_file_name` is in Long UNC (Uniform Naming Convention) format with server name, share name, and pathname.
       For example, consider a `src_file_name` of /tmp/A.h5. If that source file does not exist, the new `src_file_name` after stripping will be A.h5.
    6. `src_file_name` is in Long UNC (Uniform Naming Convention) format with an absolute drive and an absolute pathname.
       For example, consider a `src_file_name` of /tmp/A.h5. If that source file does not exist, the new `src_file_name` after stripping will be A.h5

See also
  Virtual Dataset Overview
  Supporting Functions: H5Pget_layout(), H5Pset_layout(), H5Sget_regular_hyperslab(), H5Sis_regular_hyperslab(), H5Sselect_hyperslab()
  VDS Functions: H5Pget_virtual_count(), H5Pget_virtual_dsetname(), H5Pget_virtual_filename(), H5Pget_virtual_prefix(), H5Pget_virtual_printf_gap(), H5Pget_virtual_srcspace(), H5Pget_virtual_view(), H5Pget_virtual_vspace(), H5Pset_virtual(), H5Pset_virtual_prefix(), H5Pset_virtual_printf_gap(), H5Pset_virtual_view()

Version
  1.10.2 A change was made to the method of searching for VDS source files.

Since
  1.10.0

## ◆ H5Pset_virtual_spatial_tree()

herr_t H5Pset_virtual_spatial_tree | ( | hid_t | dcpl_id,
|  | bool | use_tree )

Sets the flag to use a spatial tree for mappings.

Parameters

  [in] | dcpl_id | Dataset creation property list identifier
  [in] | use_tree | Flag for indicating whether or not a dataset should use a spatial tree for mappings

Returns
  Returns a non-negative value if successful; otherwise, returns a negative value.

H5Pset_virtual_spatial_tree() sets the use-tree flag for the dataset creation property list `dcpl_id`. Datasets created with the dataset creation property list `dcpl_id` will construct a spatial tree and use it in an attempt to optimize intersection-check operations on mappings when `use_tree` is set to true.

Use of a spatial tree will accelerate the process of searching through mappings to determine which contain intersections with the user's selection region. With the tree disabled, all mappings will simply be iterated through and checked directly.

Certain workflows may find that tree creation overhead outweighs the time saved on reads. In this case, disabling this property will lead to a performance improvement, though it is expected that almost all cases will benefit from the tree on net.

Since
  2.0.0