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Calls user-defined function for each attribute on an object


H5A_ITERATE2 ( obj_id, idx_type, order, n, op, op_data )


herr_t H5Aiterate2(
            hid_t obj_id, 
            H5_index_t idx_type, 
            H5_iter_order_t order, 
            hsize_t *n, 
            H5A_operator2_t op, 
            void *op_data, 

hid_t obj_idIN: Identifier for object to which attributes are attached; may be a group, dataset, or named datatype identifier
H5_index_t idx_typeIN: Type of index
H5_iter_order_t order    IN: Order in which to iterate over index
hsize_t *nIN/OUT: Initial and returned offset within index
H5A_operator2_t opIN: User-defined function to pass each attribute to
void *op_dataIN/OUT: User data to pass through to and to be returned by iterator operator function


H5A_ITERATE2 iterates over the attributes attached to a dataset, named datatype, or group, as specified by obj_id. For each attribute, user-provided data, op_data, with additional information as defined below, is passed to a user-defined function, op, which operates on that attribute.

The order of the iteration and the attributes iterated over are specified by three parameters: the index type, idx_type; the order in which the index is to be traversed, order; and the attribute’s position in the index, n.

The type of index specified by idx_type can be one of the following:

H5_INDEX_NAMEAn alpha-numeric index by attribute name
H5_INDEX_CRT_ORDERAn index by creation order

The order in which the index is to be traversed, as specified by order, can be one of the following:

H5_ITER_INCIteration is from beginning to end, i.e., a top-down iteration incrementing the index position at each step.
H5_ITER_DECIteration starts at the end of the index, i.e., a bottom-up iteration decrementing the index position at each step.
H5_ITER_NATIVEHDF5 iterates in the fastest-available order. No information is provided as to the order, but HDF5 ensures that each element in the index will be visited if the iteration completes successfully.

The next attribute to be operated on is specified by n, a position in the index.

For example, if idx_type, order, and n are set to H5_INDEX_NAME, H5_ITER_INC, and 5, respectively, the attribute in question is the fifth attribute from the beginning of the alpha-numeric index of attribute names. If order were set to H5_ITER_DEC, it would be the fifth attribute from the end of the index.

The parameter n is passed in on an H5A_ITERATE2 call with one value and may be returned with another value. The value passed in identifies the parameter to be operated on first; the value returned identifies the parameter to be operated on in the next step of the iteration.

The H5A_operator2_t prototype for the op parameter is as follows:

typedef herr_t (*H5A_operator2_t)( hid_t location_id/*in*/, const char *attr_name/*in*/, const H5A_info_t *ainfo/*in*/, void *op_data/*in,out*/)

The operation receives the location identifier for the group or dataset being iterated over, location_id; the name of the current object attribute, attr_name; the attribute’s info struct, ainfo; and a pointer to the operator data passed into H5Aiterate2, op_data.

Valid return values from an operator and the resulting H5A_ITERATE2 and op behavior are as follows:

  • Zero causes the iterator to continue, returning zero when all attributes have been processed.
  • A positive value causes the iterator to immediately return that positive value, indicating short-circuit success. The iterator can be restarted at the next attribute, as indicated by the return value of n.
  • A negative value causes the iterator to immediately return that value, indicating failure. The iterator can be restarted at the next attribute, as indicated by the return value of n.


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

Further note that this function returns the return value of the last operator if it was non-zero, which can be a negative value, zero if all attributes were processed, or a positive value indicating short-circuit success (see above).


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Release    C
1.8.0Function introduced in this release.

--- Last Modified: May 08, 2018 | 10:14 AM