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H5T: Datatype Interface

Datatype Object API Functions

These functions create and manipulate the datatype which describes elements of a dataset.

The C Interfaces:
General Datatype Operations
  • H5Tcreate
  • H5Topen
  • H5Tcommit
  • H5Tcommitted
  • H5Tcopy
  • H5Tequal
  • H5Tlock
  • H5Tget_class
  • H5Tget_size
  • H5Tget_super
  • H5Tclose

    Conversion Functions

  • H5Tconvert
  • H5Tfind
  • H5Tset_overflow
  • H5Tget_overflow
  • H5Tregister
  • H5Tunregister
  •        Atomic Datatype Properties
  • H5Tset_size
  • H5Tget_order
  • H5Tset_order
  • H5Tget_precision
  • H5Tset_precision
  • H5Tget_offset
  • H5Tset_offset
  • H5Tget_pad
  • H5Tset_pad
  • H5Tget_sign
  • H5Tset_sign
  • H5Tget_fields
  • H5Tset_fields
  • H5Tget_ebias
  • H5Tset_ebias
  • H5Tget_norm
  • H5Tset_norm
  • H5Tget_inpad
  • H5Tset_inpad
  • H5Tget_cset
  • H5Tset_cset
  • H5Tget_strpad
  • H5Tset_strpad
  • Variable-length Datatypes

  • H5Tvlen_create
  •        Compound Datatype Properties
  • H5Tget_nmembers
  • H5Tget_member_name
  • H5Tget_member_offset
  • H5Tget_member_dims
  • H5Tget_member_type
  • H5Tinsert
  • H5Tpack
  • H5Tinsert_array

    Enumeration Datatypes

  • H5Tenum_create
  • H5Tenum_insert
  • H5Tenum_nameof
  • H5Tenum_valueof
  • H5Tget_member_value

    Opaque Datatypes

  • H5Tset_tag
  • H5Tget_tag
  • The FORTRAN90 Interfaces:
    In general, each FORTRAN90 subroutine performs exactly the same task as the corresponding C function. The links below go to the C function descriptions, which serve as general descriptions for both. A button, under Non-C API(s) at the end of the C function description, opens an external browser window displaying the FORTRAN90-specific information. You will probably want to adjust the size and location of this external window so that both browser windows are visible and to facilitate moving easily between them.
    General Datatype Operations
  • h5tcreate_f
  • h5topen_f
  • h5tcommit_f
  • h5tcommitted_f
  • h5tcopy_f
  • h5tequal_f
  • h5tget_class_f
  • h5tget_size_f
  • h5tclose_f

    Atomic Datatype Properties

  • h5tset_size_f
  • h5tget_order_f
  • h5tset_order_f
  • h5tget_precision_f
  • h5tset_precision_f
  • h5tget_offset_f
  • h5tset_offset_f
  •        Atomic (continued)
  • h5tget_pad_f
  • h5tset_pad_f
  • h5tget_sign_f
  • h5tset_sign_f
  • h5tget_fields_f
  • h5tset_fields_f
  • h5tget_ebiass_f
  • h5tset_ebiass_f
  • h5tget_norm_f
  • h5tset_norm_f
  • h5tget_inpad_f
  • h5tset_inpad_f
  • h5tget_cset_f
  • h5tset_cset_f
  • h5tget_strpad_f
  • h5tset_strpad_f
  •        Compound Datatype Properties
  • h5tget_nmembers_f
  • h5tget_member_name_f
  • h5tget_member_offset_f
  • h5tget_member_dims_f
  • h5tget_member_type_f
  • h5tinsert_f
  • h5tpack_f
  • h5tinsert_array_f

    Enumeration Datatypes

  • h5tenum_create_f
  • h5tenum_insert_f
  • h5tenum_nameof_f
  • h5tenum_valueof_f
  • h5tget_member_value_f

    Opaque Datatypes

  • h5tset_tag_f
  • h5tget_tag_f
  • The Datatype interface, H5T, provides a mechanism to describe the storage format of individual data points of a data set and is hopefully designed in such a way as to allow new features to be easily added without disrupting applications that use the data type interface. A dataset (the H5D interface) is composed of a collection or raw data points of homogeneous type organized according to the data space (the H5S interface).

    A datatype is a collection of datatype properties, all of which can be stored on disk, and which when taken as a whole, provide complete information for data conversion to or from that datatype. The interface provides functions to set and query properties of a datatype.

    A data point is an instance of a datatype, which is an instance of a type class. We have defined a set of type classes and properties which can be extended at a later time. The atomic type classes are those which describe types which cannot be decomposed at the datatype interface level; all other classes are compound.

    See The Datatype Interface (H5T) in the HDF5 User's Guide for further information, including a complete list of all supported datatypes.


    Name: H5Topen
    Signature:
    hid_tH5Topen(hid_t loc_id, const char * name )
    Purpose:
    Opens a named datatype.
    Description:
    H5Topen opens a named datatype at the location specified by loc_id and returns an identifier for the datatype. loc_id is either a file or group identifier. The identifier should eventually be closed by calling H5Tclose() to release resources.
    Parameters:
    hid_t loc_id
    IN: A file or group identifier.
    const char * name
    IN: A datatype name, defined within the file or group identified by loc_id.
    Returns:
    Returns a named datatype identifier if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tcommit
    Signature:
    herr_tH5Tcommit(hid_t loc_id, const char * name, hid_t type )
    Purpose:
    Commits a transient datatype to a file, creating a new named datatype.
    Description:
    H5Tcommit commits a transient datatype (not immutable) to a file, turned it into a named datatype. The loc_id is either a file or group identifier which, when combined with name, refers to a new named datatype.
    Parameters:
    hid_t loc_id
    IN: A file or group identifier.
    const char * name
    IN: A datatype name.
    hid_t type
    IN: A datatype identifier.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tcommitted
    Signature:
    htri_tH5Tcommitted(hid_t type)
    Purpose:
    Determines whether a datatype is a named type or a transient type.
    Description:
    H5Tcommitted queries a type to determine whether the type specified by the type identifier is a named type or a transient type. If this function returns a positive value, then the type is named (that is, it has been committed, perhaps by some other application). Datasets which return committed datatypes with H5Dget_type() are able to share the datatype with other datasets in the same file.
    Parameters:
    hid_t type
    IN: Datatype identifier.
    Returns:
    When successful, returns a positive value, for TRUE, if the datatype has been committed, or 0 (zero), for FALSE, if the datatype has not been committed. Otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tinsert_array
    Signature:
    herr_tH5Tinsert_array(hid_t parent_id, const char *name, size_t offset, int ndims, const size_t *dim, const int *perm, hid_t member_id )
    Purpose:
    Adds an array member to a compound datatype.
    Description:
    H5Tinsert_array adds a new member to the compound datatype parent_id. The member is an array with ndims dimensionality and the size of the array is dim. The new member's name, name, must be unique within the compound datatype. The offset argument defines the byte offset of the start of the member in an instance of the compound datatype and member_id is the type identifier of the new member. The total member size should be relatively small.

    The functionality of the perm parameter has not yet been implemented. Currently, perm is best set to NULL. (When implemented, perm will specify the mapping of dimensions within a struct. At that time, a NULL value for perm will mean no mappiing change is to take place. Thus, using a value of NULL ensures that application behavior will remain unchanged upon implementation of this functionality.)

    Parameters:
    hid_t parent_id
    IN: Identifier of the parent compound datatype.
    const char *name
    IN: Name of new member.
    size_t offset
    IN: Offset to start of new member within compound datatype.
    int ndims
    IN: Dimensionality of new member. Valid values are 0 (zero) through 4 (four).
    const size_t *dim
    IN: Size of new member array.
    const int *perm
    IN: Pointer to buffer to store the permutation vector of the field.
    hid_t member_id
    IN: Identifier of the datatype of the new member.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tfind
    Signature:
    H5T_conv_t H5Tfind(hid_t src_id, hid_t dst_id, H5T_cdata_t **pcdata )
    Purpose:
    Finds a conversion function.
    Description:
    H5Tfind finds a conversion function that can handle a conversion from type src_id to type dst_id. The pcdata argument is a pointer to a pointer to type conversion data which was created and initialized by the soft type conversion function of this path when the conversion function was installed on the path.
    Parameters:
    hid_t src_id
    IN: Identifier for the source datatype.
    hid_t dst_id
    IN: Identifier for the destination datatype.
    H5T_cdata_t **pcdata
    OUT: Pointer to type conversion data.
    Returns:
    Returns a pointer to a suitable conversion function if successful. Otherwise returns NULL.

    Name: H5Tconvert
    Signature:
    herr_t H5Tconvert(hid_t src_id, hid_t dst_id, size_t nelmts, void *buf, void *background, hid_t plist_id )
    Purpose:
    Converts data from between specified datatypes.
    Description:
    H5Tconvert converts nelmts elements from the type specified by the src_id identifier to type dst_id. The source elements are packed in buf and on return the destination will be packed in buf. That is, the conversion is performed in place. The optional background buffer is an array of nelmts values of destination type which are merged with the converted values to fill in cracks (for instance, background might be an array of structs with the a and b fields already initialized and the conversion of buf supplies the c and d field values).

    The parameter plist_id contains the dataset transfer property list identifier which is passed to the conversion functions. As of Release 1.2, this parameter is only used to pass along the variable-length datatype custom allocation information.

    Parameters:
    hid_t src_id
    Identifier for the source datatype.
    hid_t dst_id
    Identifier for the destination datatype.
    size_t nelmts
    Size of array buf.
    void *buf
    Array containing pre- and post-conversion values.
    void *background
    Optional background buffer.
    hid_t plist_id
    Dataset transfer property list identifier.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.

    Name: H5Tset_overflow
    Signature:
    herr_t H5Tset_overflow(H5T_overflow_t func)
    Purpose:
    Sets the overflow handler to a specified function.
    Description:
    H5Tset_overflow sets the overflow handler to be the function specified by func. func will be called for all datatype conversions that result in an overflow.

    See the definition of H5T_overflow_t in H5Tpublic.h for documentation of arguments and return values. The prototype for H5T_overflow_t is as follows:
    herr_t (*H5T_overflow_t)(hid_t src_id, hid_t dst_id, void *src_buf, void *dst_buf);

    The NULL pointer may be passed to remove the overflow handler.

    Parameters:
    H5T_overflow_t func
    Overflow function.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.

    Name: H5Tget_overflow
    Signature: H5Tget_overflow ()
    H5T_overflow_t H5Tget_overflow(void)
    Purpose:
    Returns a pointer to the current global overflow function.
    Description:
    H5Tset_overflow returns a pointer to the current global overflow function. This is an application-defined function that is called whenever a datatype conversion causes an overflow.
    Parameters:
    None.
    Returns:
    Returns a pointer to an application-defined function if successful. Otherwise returns NULL; this can happen if no overflow handling function is registered.

    Name: H5Tcreate
    Signature:
    hid_t H5Tcreate(H5T_class_t class, size_tsize )
    Purpose:
    Creates a new dataype.
    Description:
    H5Tcreate creates a new dataype of the specified class with the specified number of bytes.

    The following datatype classes are supported with this function:

    Use H5Tcopy to create integer or floating-point datatypes.

    The datatype identifier returned from this function should be released with H5Tclose or resource leaks will result.

    Parameters:
    H5T_class_t class
    Class of datatype to create.
    size_t size
    The number of bytes in the datatype to create.
    Returns:
    Returns datatype identifier if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tvlen_create
    Signature:
    hid_t H5Tvlen_create(hid_t base_type_id )
    Purpose:
    Creates a new variable-length dataype.
    Description:
    H5Tvlen_create creates a new variable-length (VL) dataype.

    The base datatype will be the datatype that the sequence is composed of, characters for character strings, vertex coordinates for polygon lists, etc. The base type specified for the VL datatype can be of any HDF5 datatype, including another VL datatype, a compound datatype or an atomic datatype.

    When necessary, use H5Tget_super to determine the base type of the VL datatype.

    The datatype identifier returned from this function should be released with H5Tclose or resource leaks will result.

    Parameters:
    hid_t base_type_id
    Base type of datatype to create.
    See Also:
    H5Dget_vlen_buf_size
    H5Dvlen_reclaim
    Returns:
    Returns datatype identifier if successful; otherwise returns a negative value.

    Name: H5Tcopy
    Signature:
    hid_t H5Tcopy(hid_t type_id)
    Purpose:
    Copies an existing datatype.
    Description:
    H5Tcopy copies an existing datatype. The returned type is always transient and unlocked.

    The type_id argument can be either a datatype identifier, a predefined datatype (defined in H5Tpublic.h), or a dataset identifier. If type_id is a dataset identifier instead of a datatype identifier, then this function returns a transient, modifiable datatype which is a copy of the dataset's datatype.

    The datatype identifier returned should be released with H5Tclose or resource leaks will occur.

    Parameters:
    hid_t type_id
    Identifier of datatype to copy. Can be a datatype identifier, a predefined datatype (defined in H5Tpublic.h), or a dataset identifier.
    Returns:
    Returns a datatype identifier if successful; otherwise returns a negative value
    Non-C API(s):

    Name: H5Tequal
    Signature:
    htri_t H5Tequal(hid_t type_id1, hid_ttype_id2 )
    Purpose:
    Determines whether two datatype identifiers refer to the same datatype.
    Description:
    H5Tequal determines whether two datatype identifiers refer to the same datatype.
    Parameters:
    hid_t type_id1
    Identifier of datatype to compare.
    hid_t type_id2
    Identifier of datatype to compare.
    Returns:
    When successful, returns a positive value, for TRUE, if the datatype identifiers refer to the same datatype, or 0 (zero), for FALSE. Otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tlock
    Signature:
    herr_t H5Tlock(hid_t type_id )
    Purpose:
    Locks a datatype.
    Description:
    H5Tlock locks the datatype specified by the type_id identifier, making it read-only and non-destrucible. This is normally done by the library for predefined datatypes so the application does not inadvertently change or delete a predefined type. Once a datatype is locked it can never be unlocked.
    Parameters:
    hid_t type_id
    Identifier of datatype to lock.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.

    Name: H5Tget_class
    Signature:
    H5T_class_t H5Tget_class(hid_t type_id )
    Purpose:
    Returns the datatype class identifier.
    Description:
    H5Tget_class returns the datatype class identifier.

    Valid class identifiers, as defined in H5Tpublic.h, are:

    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns datatype class identifier if successful; otherwise H5T_NO_CLASS (-1).
    Non-C API(s):

    Name: H5Tget_size
    Signature:
    size_t H5Tget_size(hid_t type_id )
    Purpose:
    Returns the size of a datatype.
    Description:
    H5Tget_size returns the size of a datatype in bytes.
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns the size of the datatype in bytes if successful; otherwise 0.
    Non-C API(s):

    Name: H5Tset_size
    Signature:
    herr_t H5Tset_size(hid_t type_id, size_tsize )
    Purpose:
    Sets the total size for an atomic datatype.
    Description:
    H5Tset_size sets the total size in bytes, size, for an atomic datatype (this operation is not permitted on compound datatypes). If the size is decreased so that the significant bits of the datatype extend beyond the edge of the new size, then the `offset' property is decreased toward zero. If the `offset' becomes zero and the significant bits of the datatype still hang over the edge of the new size, then the number of significant bits is decreased. Adjusting the size of an H5T_STRING automatically sets the precision to 8*size. All datatypes have a positive size.
    Parameters:
    hid_t type_id
    Identifier of datatype to change size.
    size_t size
    Size in bytes to modify datatype.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_super
    Signature:
    hid_t H5Tget_super(hid_t type )
    Purpose:
    Returns the base datatype from which a datatype is derived.
    Description:
    H5Tget_super returns the base datatype from which the datatype type is derived.

    In the case of an enumeration type, the return value is an integer type.

    Parameters:
    hid_t type
    Datatype identifier for the derived datatype.
    Returns:
    Returns the datatype identifier for the base datatype if successful; otherwise returns a negative value.

    Name: H5Tget_order
    Signature:
    H5T_order_t H5Tget_order(hid_t type_id )
    Purpose:
    Returns the byte order of an atomic datatype.
    Description:
    H5Tget_order returns the byte order of an atomic datatype.

    Possible return values are:

    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns a byte order constant if successful; otherwise H5T_ORDER_ERROR (-1).
    Non-C API(s):

    Name: H5Tset_order
    Signature:
    herr_t H5Tset_order(hid_t type_id, H5T_order_torder )
    Purpose:
    Sets the byte ordering of an atomic datatype.
    Description:
    H5Tset_order sets the byte ordering of an atomic datatype. Byte orderings currently supported are:
    Parameters:
    hid_t type_id
    Identifier of datatype to set.
    H5T_order_t order
    Byte ordering constant.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_precision
    Signature:
    size_t H5Tget_precision(hid_t type_id )
    Purpose:
    Returns the precision of an atomic datatype.
    Description:
    H5Tget_precision returns the precision of an atomic datatype. The precision is the number of significant bits which, unless padding is present, is 8 times larger than the value returned by H5Tget_size().
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns the number of significant bits if successful; otherwise 0.
    Non-C API(s):

    Name: H5Tset_precision
    Signature:
    herr_t H5Tset_precision(hid_t type_id, size_tprecision )
    Purpose:
    Sets the precision of an atomic datatype.
    Description:
    H5Tset_precision sets the precision of an atomic datatype. The precision is the number of significant bits which, unless padding is present, is 8 times larger than the value returned by H5Tget_size().

    If the precision is increased then the offset is decreased and then the size is increased to insure that significant bits do not "hang over" the edge of the datatype.

    Changing the precision of an H5T_STRING automatically changes the size as well. The precision must be a multiple of 8.

    When decreasing the precision of a floating point type, set the locations and sizes of the sign, mantissa, and exponent fields first.

    Parameters:
    hid_t type_id
    Identifier of datatype to set.
    size_t precision
    Number of bits of precision for datatype.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_offset
    Signature:
    size_t H5Tget_offset(hid_t type_id )
    Purpose:
    Retrieves the bit offset of the first significant bit.
    Description:
    H5Tget_offset retrieves the bit offset of the first significant bit. The signficant bits of an atomic datum can be offset from the beginning of the memory for that datum by an amount of padding. The `offset' property specifies the number of bits of padding that appear to the "right of" the value. That is, if we have a 32-bit datum with 16-bits of precision having the value 0x1122 then it will be layed out in memory as (from small byte address toward larger byte addresses):

    Byte Position Big-Endian Offset=0 Big-Endian Offset=16 Little-Endian Offset=0 Little-Endian Offset=16
    0: [ pad] [0x11] [0x22] [ pad]
    1: [ pad] [0x22] [0x11] [ pad]
    2: [0x11] [ pad] [ pad] [0x22]
    3: [0x22] [ pad] [ pad] [0x11]
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns a positive offset value if successful; otherwise 0.
    Non-C API(s):

    Name: H5Tset_offset
    Signature:
    herr_t H5Tset_offset(hid_t type_id, size_t offset )
    Purpose:
    Sets the bit offset of the first significant bit.
    Description:
    H5Tset_offset sets the bit offset of the first significant bit. The signficant bits of an atomic datum can be offset from the beginning of the memory for that datum by an amount of padding. The `offset' property specifies the number of bits of padding that appear to the "right of" the value. That is, if we have a 32-bit datum with 16-bits of precision having the value 0x1122 then it will be layed out in memory as (from small byte address toward larger byte addresses):

    Byte Position Big-Endian Offset=0 Big-Endian Offset=16 Little-Endian Offset=0 Little-Endian Offset=16
    0: [ pad] [0x11] [0x22] [ pad]
    1: [ pad] [0x22] [0x11] [ pad]
    2: [0x11] [ pad] [ pad] [0x22]
    3: [0x22] [ pad] [ pad] [0x11]

    If the offset is incremented then the total size is incremented also if necessary to prevent significant bits of the value from hanging over the edge of the datatype.

    The offset of an H5T_STRING cannot be set to anything but zero.

    Parameters:
    hid_t type_id
    Identifier of datatype to set.
    size_t offset
    Offset of first significant bit.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_pad
    Signature:
    herr_t H5Tget_pad(hid_t type_id, H5T_pad_t * lsb, H5T_pad_t * msb )
    Purpose:
    Retrieves the padding type of the least and most-significant bit padding.
    Description:
    H5Tget_pad retrieves the padding type of the least and most-significant bit padding. Valid types are:
    Parameters:
    hid_t type_id
    IN: Identifier of datatype to query.
    H5T_pad_t * lsb
    OUT: Pointer to location to return least-significant bit padding type.
    H5T_pad_t * msb
    OUT: Pointer to location to return most-significant bit padding type.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tset_pad
    Signature:
    herr_t H5Tset_pad(hid_t type_id, H5T_pad_t lsb, H5T_pad_t msb )
    Purpose:
    Sets the least and most-significant bits padding types.
    Description:
    H5Tset_pad sets the least and most-significant bits padding types.
    Parameters:
    hid_t type_id
    Identifier of datatype to set.
    H5T_pad_t lsb
    Padding type for least-significant bits.
    H5T_pad_t msb
    Padding type for most-significant bits.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_sign
    Signature:
    H5T_sign_t H5Tget_sign(hid_t type_id )
    Purpose:
    Retrieves the sign type for an integer type.
    Description:
    H5Tget_sign retrieves the sign type for an integer type. Valid types are:
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns a valid sign type if successful; otherwise H5T_SGN_ERROR (-1).
    Non-C API(s):

    Name: H5Tset_sign
    Signature:
    herr_t H5Tset_sign(hid_t type_id, H5T_sign_t sign )
    Purpose:
    Sets the sign proprety for an integer type.
    Description:
    H5Tset_sign sets the sign proprety for an integer type.
    Parameters:
    hid_t type_id
    Identifier of datatype to set.
    H5T_sign_t sign
    Sign type.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_fields
    Signature:
    herr_t H5Tget_fields(hid_t type_id, size_t *spos, size_t *epos, size_t *esize, size_t *mpos, size_t *msize )
    Purpose:
    Retrieves floating point datatype bit field information.
    Description:
    H5Tget_fields retrieves information about the locations of the various bit fields of a floating point datatype. The field positions are bit positions in the significant region of the datatype. Bits are numbered with the least significant bit number zero. Any (or even all) of the arguments can be null pointers.
    Parameters:
    hid_t type_id
    IN: Identifier of datatype to query.
    size_t *spos
    OUT: Pointer to location to return floating-point sign bit.
    size_t *epos
    OUT: Pointer to location to return exponent bit-position.
    size_t *esize
    OUT: Pointer to location to return size of exponent in bits.
    size_t *mpos
    OUT: Pointer to location to return mantissa bit-position.
    size_t *msize
    OUT: Pointer to location to return size of mantissa in bits.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tset_fields
    Signature:
    herr_t H5Tset_fields(hid_t type_id, size_t spos, size_t epos, size_t esize, size_t mpos, size_t msize )
    Purpose:
    Sets locations and sizes of floating point bit fields.
    Description:
    H5Tset_fields sets the locations and sizes of the various floating-point bit fields. The field positions are bit positions in the significant region of the datatype. Bits are numbered with the least significant bit number zero.

    Fields are not allowed to extend beyond the number of bits of precision, nor are they allowed to overlap with one another.

    Parameters:
    hid_t type_id
    Identifier of datatype to set.
    size_t spos
    Sign position, i.e., the bit offset of the floating-point sign bit.
    size_t epos
    Exponent bit position.
    size_t esize
    Size of exponent in bits.
    size_t mpos
    Mantissa bit position.
    size_t msize
    Size of mantissa in bits.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_ebias
    Signature:
    size_t H5Tget_ebias(hid_t type_id )
    Purpose:
    Retrieves the exponent bias of a floating-point type.
    Description:
    H5Tget_ebias retrieves the exponent bias of a floating-point type.
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns the bias if successful; otherwise 0.
    Non-C API(s):

    Name: H5Tset_ebias
    Signature:
    herr_t H5Tset_ebias(hid_t type_id, size_t ebias )
    Purpose:
    Sets the exponent bias of a floating-point type.
    Description:
    H5Tset_ebias sets the exponent bias of a floating-point type.
    Parameters:
    hid_t type_id
    Identifier of datatype to set.
    size_t ebias
    Exponent bias value.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_norm
    Signature:
    H5T_norm_t H5Tget_norm(hid_t type_id )
    Purpose:
    Retrieves mantissa normalization of a floating-point datatype.
    Description:
    H5Tget_norm retrieves the mantissa normalization of a floating-point datatype. Valid normalization types are:
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns a valid normalization type if successful; otherwise H5T_NORM_ERROR (-1).
    Non-C API(s):

    Name: H5Tset_norm
    Signature:
    herr_t H5Tset_norm(hid_t type_id, H5T_norm_t norm )
    Purpose:
    Sets the mantissa normalization of a floating-point datatype.
    Description:
    H5Tset_norm sets the mantissa normalization of a floating-point datatype. Valid normalization types are:
    Parameters:
    hid_t type_id
    Identifier of datatype to set.
    H5T_norm_t norm
    Mantissa normalization type.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_inpad
    Signature:
    H5T_pad_t H5Tget_inpad(hid_t type_id )
    Purpose:
    Retrieves the internal padding type for unused bits in floating-point datatypes.
    Description:
    H5Tget_inpad retrieves the internal padding type for unused bits in floating-point datatypes. Valid padding types are:
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns a valid padding type if successful; otherwise H5T_PAD_ERROR (-1).
    Non-C API(s):

    Name: H5Tset_inpad
    Signature:
    herr_t H5Tset_inpad(hid_t type_id, H5T_pad_t inpad )
    Purpose:
    Fills unused internal floating point bits.
    Description:
    If any internal bits of a floating point type are unused (that is, those significant bits which are not part of the sign, exponent, or mantissa), then H5Tset_inpad will be filled according to the value of the padding value property inpad. Valid padding types are:
    Parameters:
    hid_t type_id
    Identifier of datatype to modify.
    H5T_pad_t pad
    Padding type.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_cset
    Signature:
    H5T_cset_t H5Tget_cset(hid_t type_id )
    Purpose:
    Retrieves the character set type of a string datatype.
    Description:
    H5Tget_cset retrieves the character set type of a string datatype. Valid character set types are:
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns a valid character set type if successful; otherwise H5T_CSET_ERROR (-1).
    Non-C API(s):

    Name: H5Tset_cset
    Signature:
    herr_t H5Tset_cset(hid_t type_id, H5T_cset_t cset )
    Purpose:
    Sets character set to be used.
    Description:
    H5Tset_cset the character set to be used.

    HDF5 is able to distinguish between character sets of different nationalities and to convert between them to the extent possible. Valid character set types are:

    Parameters:
    hid_t type_id
    Identifier of datatype to modify.
    H5T_cset_t cset
    Character set type.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_strpad
    Signature:
    H5T_str_t H5Tget_strpad(hid_t type_id )
    Purpose:
    Retrieves the string padding method for a string datatype.
    Description:
    H5Tget_strpad retrieves the string padding method for a string datatype. Valid string padding types are:
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns a valid string padding type if successful; otherwise H5T_STR_ERROR (-1).
    Non-C API(s):

    Name: H5Tset_strpad
    Signature:
    herr_t H5Tset_strpad(hid_t type_id, H5T_str_t strpad )
    Purpose:
    Defines the storage mechanism for character strings.
    Description:
    H5Tset_strpad defines the storage mechanism for the string.

    The method used to store character strings differs with the programming language:

    Valid string padding values, as passed in the parameter strpad, are as follows:

    When converting from a longer string to a shorter string, the behavior is as follows. If the short string is H5T_STR_NULLPAD or H5T_STR_SPACEPAD, then the string is simply truncated. If the short string is H5T_STR_NULLTERM, it is truncated and a null terminator is appended.

    When converting from a shorter string to a longer string, the long string is padded on the end by appending nulls or spaces.

    Parameters:
    hid_t type_id
    Identifier of datatype to modify.
    H5T_str_t strpad
    String padding type.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_nmembers
    Signature:
    int H5Tget_nmembers(hid_t type_id )
    Purpose:
    Retrieves the number of fields in a compound datatype.
    Description:
    H5Tget_nmembers retrieves the number of fields a compound datatype has.
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    Returns:
    Returns number of members datatype has if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_member_name
    Signature:
    char * H5Tget_member_name(hid_t type_id, int field_idx )
    Purpose:
    Retrieves the name of a field of a compound datatype.
    Description:
    H5Tget_member_name retrieves the name of a field of a compound datatype. Fields are stored in no particular order, with indexes 0 through N-1, where N is the value returned by H5Tget_nmembers(). The name of the field is allocated with malloc() and the caller is responsible for freeing the memory used by the name.
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    int field_idx
    Field index (0-based) of the field name to retrieve.
    Returns:
    Returns a valid pointer if successful; otherwise NULL.
    Non-C API(s):

    Name: H5Tget_member_offset
    Signature:
    size_t H5Tget_member_offset(hid_t type_id, int memb_no )
    Purpose:
    Retrieves the offset of a field of a compound datatype.
    Description:
    H5Tget_member_offset retrieves the byte offset of the beginning of a field within a compound datatype with respect to the beginning of the compound data type datum.
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    int memb_no
    Number of the field whose offset is requested.
    Returns:
    Returns the byte offset of the field if successful; otherwise returns 0 (zero). Note that zero is a valid offset and that this function will fail only if a call to H5Tget_member_dims() fails with the same arguments.
    Non-C API(s):

    Name: H5Tget_member_dims
    Signature:
    int H5Tget_member_dims(hid_t type_id, int field_idx, size_t *dims, int *perm )
    Purpose:
    Returns the dimensionality of the field.
    Description:
    H5Tget_member_dims returns the dimensionality of the field. The dimensions and permuation vector are returned through arguments dims and perm, both arrays of at least four elements. Either (or even both) may be null pointers.
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    int field_idx
    Field index (0-based) of the field dims to retrieve.
    size_t * dims
    Pointer to buffer to store the dimensions of the field.
    int * perm
    Pointer to buffer to store the permutation vector of the field.
    Returns:
    Returns the number of dimensions, a number from 0 to 4, if successful. Otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_member_type
    Signature:
    hid_t H5Tget_member_type(hid_t type_id, int field_idx )
    Purpose:
    Returns the datatype of the specified member.
    Description:
    H5Tget_member_type returns the datatype of the specified member. The caller should invoke H5Tclose() to release resources associated with the type.
    Parameters:
    hid_t type_id
    Identifier of datatype to query.
    int field_idx
    Field index (0-based) of the field type to retrieve.
    Returns:
    Returns the identifier of a copy of the datatype of the field if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tinsert
    Signature:
    herr_t H5Tinsert(hid_t type_id, const char * name, size_t offset, hid_t field_id )
    Purpose:
    Adds a new member to a compound datatype.
    Description:
    H5Tinsert adds another member to the compound datatype type_id. The new member has a name which must be unique within the compound datatype. The offset argument defines the start of the member in an instance of the compound datatype, and field_id is the datatype identifier of the new member.

    Note: Members of a compound datatype do not have to be atomic datatypes; a compound datatype can have a member which is a compound datatype.

    Parameters:
    hid_t type_id
    Identifier of compound datatype to modify.
    const char * name
    Name of the field to insert.
    size_t offset
    Offset in memory structure of the field to insert.
    hid_t field_id
    Datatype identifier of the field to insert.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tpack
    Signature:
    herr_t H5Tpack(hid_t type_id )
    Purpose:
    Recursively removes padding from within a compound datatype.
    Description:
    H5Tpack recursively removes padding from within a compound datatype to make it more efficient (space-wise) to store that data.
    Parameters:
    hid_t type_id
    Identifier of datatype to modify.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tregister
    Signature:
    herr_t H5Tregister(H5T_pers_t pers, const char * name, hid_t src_id, hid_t dst_id, H5T_conv_t func )
    Purpose:
    Registers a conversion function.
    Description:
    H5Tregister registers a hard or soft conversion function for a datatype conversion path.

    The parameter pers indicates whether a conversion function is hard (H5T_PERS_HARD) or soft (H5T_PERS_SOFT).

    A conversion path can have only one hard function. When pers is H5T_PERS_HARD, func replaces any previous hard function. If pers is H5T_PERS_HARD and func is the null pointer, then any hard function registered for this path is removed.

    When pers is H5T_PERS_SOFT, H5Tregister adds the function to the end of the master soft list and replaces the soft function in all applicable existing conversion paths. Soft functions are used when determining which conversion function is appropriate for this path.

    The name is used only for debugging and should be a short identifier for the function.

    The path is specified by the source and destination datatypes src_id and dst_id. For soft conversion functions, only the class of these types is important.

    The type of the conversion function pointer is declared as:

    typedef herr_t (*H5T_conv_t) (hid_t src_id, hid_t dst_id, H5T_cdata_t *cdata, size_t nelmts, size_t stride, void *buf, void *bkg, hid_t dset_xfer_plist);
    Parameters:
    H5T_pers_t pers
    H5T_PERS_HARD for hard conversion functions; H5T_PERS_SOFT for soft conversion functions.
    const char * name
    Name displayed in diagnostic output.
    hid_t src_id
    Identifier of source datatype.
    hid_t dst_id
    Identifier of destination datatype.
    H5T_conv_t func
    Function to convert between source and destination datatypes.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.

    Name: H5Tunregister
    Signature:
    herr_t H5Tunregister(H5T_conv_t func )
    Purpose:
    Removes a conversion function from all conversion paths.
    Description:
    H5Tunregister removes a conversion function from all conversion paths.

    The conversion function pointer type declaration is described in H5Tregister.

    Parameters:
    H5T_conv_t func
    Function to remove from conversion paths.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.

    Name: H5Tenum_create
    Signature:
    hid_t H5Tenum_create(hid_t parent_id )
    Purpose:
    Creates a new enumeration datatype.
    Description:
    H5Tenum_create creates a new enumeration datatype based on the specified base datatype, parent_id, which must be an integer type.
    Parameters:
    hid_t parent_id
    IN: Datatype identifier for the base datatype.
    Returns:
    Returns the datatype identifier for the new enumeration datatype if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tenum_insert
    Signature:
    herr_t H5Tenum_insert(hid_t type, const char *name, void *value )
    Purpose:
    Inserts a new enumeration datatype member.
    Description:
    H5Tenum_insert inserts a new enumeration datatype member into an enumeration datatype.

    type is the enumeration datatype, name is the name of the new member, and value points to the value of the new member.

    name and value must both be unique within type.

    value points to data which is of the datatype defined when the enumeration datatype was created.

    Parameters:
    hid_t type
    IN: Datatype identifier for the enumeration datatype.
    const char *name
    IN: Name of the new member.
    void *value
    IN: Pointer to the value of the new member.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tenum_nameof
    Signature:
    herr_t H5Tenum_nameof(hid_t type void *value, char *name, size_t size )
    Purpose:
    Returns the symbol name corresponding to a specified member of an enumeration datatype.
    Description:
    H5Tenum_nameof finds the symbol name that corresponds to the specified value of the enumeration datatype type.

    At most size characters of the symbol name are copied into the name buffer. If the entire symbol name and null terminator do not fit in the name buffer, then as many characters as possible are copied (not null terminated) and the function fails.

    Parameters:
    hid_t type
    IN: Enumeration datatype identifier.
    void *value,
    IN: Value of the enumeration datatype.
    char *name,
    OUT: Buffer for output of the symbol name.
    size_t size
    IN: Anticipated size of the symbol name, in bytes (characters).
    Returns:
    Returns a non-negative value if successful. Otherwise returns a negative value and, if size allows it, the first character of name is set to NULL.
    Non-C API(s):

    Name: H5Tenum_valueof
    Signature:
    herr_t H5Tenum_valueof(hid_t type char *name, void *value )
    Purpose:
    Returns the value corresponding to a specified member of an enumeration datatype.
    Description:
    H5Tenum_valueof finds the value that corresponds to the specified name of the enumeration datatype type.

    The value argument should be at least as large as the value of H5Tget_size(type) in order to hold the result.

    Parameters:
    hid_t type
    IN: Enumeration datatype identifier.
    const char *name,
    IN: Symbol name of the enumeration datatype.
    void *value,
    OUT: Buffer for output of the value of the enumeration datatype.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_member_value
    Signature:
    hid_t H5Tget_member_value(hid_t type int memb_no, void *value )
    Purpose:
    Returns the value of an enumeration datatype member.
    Description:
    H5Tget_member_value returns the value of the enumeration datatype member memb_no.

    The member value is returned in a user-supplied buffer pointed to by value.

    Parameters:
    hid_t type
    IN: Datatype identifier for the enumeration datatype.
    int memb_no,
    IN: Number of the enumeration datatype member.
    void *value
    OUT: Pointer to a buffer for output of the value of the enumeration datatype member.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tset_tag
    Signature:
    herr_t H5Tset_tag(hid_t type_id const char *tag )
    Purpose:
    Tags an opaque datatype.
    Description:
    H5Tset_tag tags an opaque datatype type_id with a unique ASCII identifier tag.
    Parameters:
    hid_t type_id
    IN: Datatype identifier for the opaque datatype to be tagged.
    const char *tag
    IN: Unique ASCII string with which the opaque datatype is to be tagged.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Name: H5Tget_tag
    Signature:
    char *H5Tget_tag(hid_t type_id )
    Purpose:
    Gets the tag associated with an opaque datatype.
    Description:
    H5Tget_tag returns the tag associated with the opaque datatype type_id.

    The tag is returned via a pointer to an allocated string, which the caller must free.

    Parameters:
    hid_t type_id
    Datatype identifier for the opaque datatype.
    Returns:
    Returns a pointer to an allocated string if successful; otherwise returns NULL.
    Non-C API(s):

    Name: H5Tclose
    Signature:
    herr_t H5Tclose(hid_t type_id )
    Purpose:
    Releases a datatype.
    Description:
    H5Tclose releases a datatype. Further access through the datatype identifier is illegal. Failure to release a datatype with this call will result in resource leaks.
    Parameters:
    hid_t type_id
    Identifier of datatype to release.
    Returns:
    Returns a non-negative value if successful; otherwise returns a negative value.
    Non-C API(s):

    Introduction to HDF5 
    HDF5 User Guide 
    Other HDF5 documents and links 
    And in this document, the HDF5 Reference Manual  
    H5   H5A   H5D   H5E   H5F   H5G   H5I  
    H5P   H5R   H5RA   H5S   H5T   H5Z   Tools  

    HDF Help Desk
    Last modified: 14 July 2000
    Describes HDF5 Version 1.3 (Unrelased development version. Dynamic.)