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

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HDF5 Dimension Scales APIs (H5DS)

## Detailed Description

Creating and manipulating HDF5 datasets that are associated with the dimension of another HDF5 dataset (H5DS)

Note
  Programming hints:
  To use any of these functions or subroutines, you must first include the relevant include file (C) or module (Fortran) in your application.
  The following line includes the HDF5 Dimension Scale package, H5DS, in C applications:
  #include "hdf5_hl.h"
  This line includes the H5DS module in Fortran applications:
  use h5ds
  h5ds
  This module contains Fortran interfaces for H5DS.
  Definition H5DSff.F90:35

- H5DSwith_new_ref
  Determines if new references are used with dimension scales.
- H5DSattach_scale
  Attach dimension scale dsid to dimension idx of dataset did.
- H5DSdetach_scale
  Detach dimension scale dsid from the dimension idx of Dataset did.
- H5DSget_label
  Read the label for dimension idx of did into buffer label.
- H5DSget_num_scales
  Determines how many Dimension Scales are attached to dimension idx of did.
- H5DSget_scale_name
  Retrieves name of scale did into buffer name.
- H5DSis_attached
  Report if dimension scale dsid is currently attached to dimension idx of dataset did.
- H5DSis_scale
  Determines whether dset is a Dimension Scale.
- H5DSiterate_scales
  Iterates the operation visitor through the scales attached to dimension dim.
- H5DSset_label
  Set label for the dimension idx of did to the value label.
- H5DSset_scale
  Convert dataset dsid to a dimension scale, with optional name, dimname.

## Functions
H5HL_DLL herr_t | H5DSattach_scale (hid_t did, hid_t dsid, unsigned int idx)
| Attach dimension scale `dsid` to dimension `idx` of dataset did.
H5HL_DLL herr_t | H5DSdetach_scale (hid_t did, hid_t dsid, unsigned int idx)
| Detach dimension scale `dsid` from the dimension `idx` of dataset `did`.
H5HL_DLL ssize_t | H5DSget_label (hid_t did, unsigned int idx, char *label, size_t size)
| Read the label for dimension `idx` of `did` into buffer `label`.
H5HL_DLL int | H5DSget_num_scales (hid_t did, unsigned int idx)
| Determines how many Dimension Scales are attached to dimension `idx` of `did`.
H5HL_DLL ssize_t | H5DSget_scale_name (hid_t did, char *name, size_t size)
| Retrieves name of scale `did` into buffer `name`.
H5HL_DLL htri_t | H5DSis_attached (hid_t did, hid_t dsid, unsigned int idx)
| Report if dimension scale `dsid` is currently attached to dimension `idx` of dataset `did`.
H5HL_DLL htri_t | H5DSis_scale (hid_t did)
| Determines whether `did` is a Dimension Scale.
H5HL_DLL herr_t | H5DSiterate_scales (hid_t did, unsigned int dim, int *idx, H5DS_iterate_t visitor, void *visitor_data)
| Iterates the operation visitor through the scales attached to dimension `dim`.
H5HL_DLL herr_t | H5DSset_label (hid_t did, unsigned int idx, const char *label)
| Set label for the dimension `idx` of `did` to the value `label`.
H5HL_DLL herr_t | H5DSset_scale (hid_t dsid, const char *dimname)
| Convert dataset `dsid` to a dimension scale, with optional name, `dimname`.
H5HL_DLL herr_t | H5DSwith_new_ref (hid_t obj_id, bool *with_new_ref)
| Determines if new references are used with dimension scales.

## Function Documentation

## ◆ H5DSattach_scale()

H5HL_DLL herr_t H5DSattach_scale | ( | hid_t | did,
|  | hid_t | dsid,
|  | unsigned int | idx )

Attach dimension scale `dsid` to dimension `idx` of dataset did.

Parameters

  [in] | did | The dataset
  [in] | dsid | The scale to be attached
  [in] | idx | The dimension of `did` that `dsid` is associated with

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

Define Dimension Scale `dsid` to be associated with dimension `idx` of dataset `did`.

Entries are created in the DIMENSION_LIST and REFERENCE_LIST attributes, as defined in Storage Profile section of the HDF5 High Level Dimension Scales.

Fails if:

- Bad arguments
- If `dsid` is not a Dimension Scale
- If `did` is a Dimension Scale (A Dimension Scale cannot have scales.)

Note
  The Dimension Scale `dsid` can be attached to the same dimension more than once, which has no effect.

## ◆ H5DSdetach_scale()

H5HL_DLL herr_t H5DSdetach_scale | ( | hid_t | did,
|  | hid_t | dsid,
|  | unsigned int | idx )

Detach dimension scale `dsid` from the dimension `idx` of dataset `did`.

Parameters

  [in] | did | The dataset
  [in] | dsid | The scale to be detached
  [in] | idx | The dimension of `did` to detach

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

If possible, deletes association of Dimension Scale `dsid` with dimension `idx` of dataset `did`. This deletes the entries in the DIMENSION_LIST and REFERENCE_LIST attributes, as defined in Storage Profile section of the HDF5 High Level Dimension Scales.

Fails if:

- Bad arguments
- The dataset `did` or `dsid` do not exist
- The `dsid` is not a Dimension Scale
- `dsid` is not attached to `did`

Note
  A scale may be associated with more than dimension of the same dataset. If so, the detach operation only deletes one of the associations, for `did`.

## ◆ H5DSget_label()

H5HL_DLL ssize_t H5DSget_label | ( | hid_t | did,
|  | unsigned int | idx,
|  | char * | label,
|  | size_t | size )

Read the label for dimension `idx` of `did` into buffer `label`.

Parameters

  [in] | did | The dataset
  [in] | idx | The dimension
  [out] | label | The label
  [in] | size | The length of the label buffer

Returns
  Upon success, size of label or zero if no label found. Negative if fail.

Returns the value of the DIMENSION_LABELS for dimension `idx` of dataset `did`, if set. Up to `size` characters of the name are copied into the buffer `label`. If the label is longer than `size`, it will be truncated to fit. The parameter `size` is set to the size of the returned `label`.

If `did` has no label, the return value of `label` is NULL.

Fails if:

- Bad arguments

## ◆ H5DSget_num_scales()

H5HL_DLL int H5DSget_num_scales | ( | hid_t | did,
|  | unsigned int | idx )

Determines how many Dimension Scales are attached to dimension `idx` of `did`.

Parameters

  [in] | did | The dataset to query
  [in] | idx | The dimension of `did` to query

Returns
  Returns the number of Dimension Scales associated with `did`, if successful, otherwise returns a negative value.

H5DSget_num_scales() determines how many Dimension Scales are attached to dimension `idx` of dataset `did`.

## ◆ H5DSget_scale_name()

H5HL_DLL ssize_t H5DSget_scale_name | ( | hid_t | did,
|  | char * | name,
|  | size_t | size )

Retrieves name of scale `did` into buffer `name`.

Parameters

  [in] | did | Dimension scale identifier
  [out] | name | Buffer to contain the returned name
  [in] | size | Size in bytes, of the `name` buffer

Returns
  Upon success, the length of the scale name or zero if no name found. Negative if fail.

H5DSget_scale_name() retrieves the name attribute for scale `did`.

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

If the length of the name, which determines the required value of `size`, is unknown, a preliminary H5DSget_scale_name() call can be made by setting `name` to NULL. The return value of this call will be the size of the scale name; that value plus one (1) can then be assigned to `size` for a second H5DSget_scale_name() call, which will retrieve the actual name. (The value passed in with the parameter `size` must be one greater than size in bytes of the actual name in order to accommodate the null terminator; if `size` is set to the exact size of the name, the last byte passed back will contain the null terminator and the last character will be missing from the name passed back to the calling application.)

## ◆ H5DSis_attached()

H5HL_DLL htri_t H5DSis_attached | ( | hid_t | did,
|  | hid_t | dsid,
|  | unsigned int | idx )

Report if dimension scale `dsid` is currently attached to dimension `idx` of dataset `did`.

Parameters

  [in] | did | The dataset
  [in] | dsid | The scale to be attached
  [in] | idx | The dimension of `did` that `dsid` is associated with

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

Report if dimension scale `dsid` is currently attached to dimension `idx` of dataset `did`.

Fails if:

- Bad arguments
- If `dsid` is not a Dimension Scale
- The `dsid` is not a Dimension Scale
- If `did` is a Dimension Scale (A Dimension Scale cannot have scales.)

## ◆ H5DSis_scale()

H5HL_DLL htri_t H5DSis_scale | ( | hid_t | did | ) |

Determines whether `did` is a Dimension Scale.

Parameters

  [in] | did | The dataset to query

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

H5DSis_scale() determines if `did` is a Dimension Scale, i.e., has class="DIMENSION_SCALE").

## ◆ H5DSiterate_scales()

H5HL_DLL herr_t H5DSiterate_scales | ( | hid_t | did,
|  | unsigned int | dim,
|  | int * | idx,
|  | H5DS_iterate_t | visitor,
|  | void * | visitor_data )

Iterates the operation visitor through the scales attached to dimension `dim`.

Parameters

  [in] | did | The dataset
  [in] | dim | The dimension of dataset `did`
  [in,out] | idx | Input the index to start iterating, output the next index to visit. If NULL, start at the first position.
  [in] | visitor | The visitor function
  [in] | visitor_data | Arbitrary data to pass to the visitor function

Returns
  Returns the return value of the last operator if it was non-zero, or zero if all scales were processed.

H5DSiterate_scales() iterates over the scales attached to dimension `dim` of dataset `did`. For each scale in the list, the `visitor_data` and some additional information, specified below, are passed to the `visitor` function. The iteration begins with the `idx` object in the group and the next element to be processed by the operator is returned in `idx`. If `idx` is NULL, then the iterator starts at the first group member; since no stopping point is returned in this case, the iterator cannot be restarted if one of the calls to its operator returns non-zero.

The prototype for H5DS_iterate_t is:

typedef herr_t (*H5DS_iterate_t)(hid_t dset, unsigned dim, hid_t scale, void *visitor_data);

The operation receives the Dimension Scale dataset identifier, `scale`, and the pointer to the operator data passed in to H5DSiterate_scales(), `visitor_data`.

The return values from an operator are:

- Zero causes the iterator to continue, returning zero when all group members have been processed.
- Positive causes the iterator to immediately return that positive value, indicating short-circuit success. The iterator can be restarted at the next group member.
- Negative causes the iterator to immediately return that value, indicating failure. The iterator can be restarted at the next group member.

H5DSiterate_scales() assumes that the scales of the dimension identified by `dim` remain unchanged through the iteration. If the membership changes during the iteration, the function's behavior is undefined.

## ◆ H5DSset_label()

H5HL_DLL herr_t H5DSset_label | ( | hid_t | did,
|  | unsigned int | idx,
|  | const char * | label )

Set label for the dimension `idx` of `did` to the value `label`.

Parameters

  [in] | did | The dataset
  [in] | idx | The dimension
  [in] | label | The label

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

Sets the DIMENSION_LABELS for dimension `idx` of dataset `did`. If the dimension had a label, the new value replaces the old.

Fails if:

- Bad arguments

## ◆ H5DSset_scale()

H5HL_DLL herr_t H5DSset_scale | ( | hid_t | dsid,
|  | const char * | dimname )

Convert dataset `dsid` to a dimension scale, with optional name, `dimname`.

Parameters

  [in] | dsid | The dataset to be made a Dimemsion Scale
  [in] | dimname | The dimension name (optional), NULL if the dimension has no name.

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

The dataset `dsid` is converted to a Dimension Scale dataset, as defined above. Creates the CLASS attribute, set to the value "DIMENSION_SCALE" and an empty REFERENCE_LIST attribute, as described in Storage Profile section of the HDF5 High Level Dimension Scales.

If `dimname` is specified, then an attribute called NAME is created, with the value `dimname`.

Fails if:

- Bad arguments
- If `dsid` is already a scale
- If `dsid` is a dataset which already has dimension scales

If the dataset was created with the Table, Image, or Palette interface [9], it is not recommended to convert to a Dimension Scale. (These Datasets will have a CLASS Table, Image, or Palette.)

Todo
  what is [9] after Palette interface?

## ◆ H5DSwith_new_ref()

H5HL_DLL herr_t H5DSwith_new_ref | ( | hid_t | obj_id,
|  | bool * | with_new_ref )

Determines if new references are used with dimension scales.

Parameters

  [in] | obj_id | Object identifier
  [out] | with_new_ref | New references are used or not

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

H5DSwith_new_ref() takes any object identifier and checks if new references are used for dimension scales. Currently, new references are used when non-native VOL connector is used or when H5_DIMENSION_SCALES_WITH_NEW_REF is set up via configure option.