H5A_ITERATE_BY_NAME iterates over the attributes attached to the dataset or group specified with
obj_name. 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.
loc_id fully specifies the object to which these attributes are attached,
obj_name should be
'.' (a dot).
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,
The type of index specified by
idx_type can be one of the following:
|An alpha-numeric index by attribute name|
|An index by creation order|
The order in which the index is to be traversed, as specified by
order, can be one of the following:
|Iteration is from beginning to end, i.e., a top-down iteration incrementing the index position at each step.|
|Iteration starts at the end of the index, i.e., a bottom-up iteration decrementing the index position at each step.|
|HDF5 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
n are set to
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.
n is passed in on an
H5Aiterate_by_name 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.
H5A_operator2_t prototype for the
op parameter is as follows:
typedef herr_t (*
location_id/*in*/, const char *
attr_name/*in*/, const H5A_info_t *
ainfo/*in*/, void *
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
Valid return values from an operator and the resulting
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
- 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
The link access property list,
lapl_id, may provide information regarding the properties of links required to access the object,
obj_name. See “Link Access Properties” in the H5P APIs.