- Created by Barbara Jones, last modified on Feb 19, 2020
H5O_VISIT2
Recursively visits all objects accessible from a specified object
As of HDF5-1.12 this function has been deprecated in favor of the function H5O_VISIT3 or the macro H5O_VISIT.
Procedure:
H5O_VISIT2 ( obj_id, idx_type, order, op, op_data, fields)
Signature:
herr_t H5Ovisit2 ( hid_t obj_id, H5_index_t idx_type, H5_iter_order_t order, H5O_iterate1_t op, void *op_data, unsigned fields )
SUBROUTINE h5ovisit_f(object_id, index_type, order, op, op_data, &
return_value, hdferr, fields)
INTEGER(HID_T), INTENT(IN) :: object_id
INTEGER, INTENT(IN) :: index_type
INTEGER, INTENT(IN) :: order
TYPE(C_FUNPTR):: op
TYPE(C_PTR) :: op_data
INTEGER, INTENT(OUT) :: return_value
INTEGER, INTENT(OUT) :: hdferr
INTEGER, INTENT(IN), OPTIONAL :: fields
Parameters:
hid_t obj_id | IN: Location identifier of the object at which the recursive iteration begins; may be a file, group, dataset, named datatype or attribute identifier |
H5_index_t idx_type | IN: Type of index; valid values include: H5_INDEX_NAME H5_INDEX_CRT_ORDER |
H5_iter_order_t order | IN: Order in which index is traversed; valid values include: H5_ITER_DEC H5_ITER_INC H5_ITER_NATIVE |
H5O_iterate1_t op | IN: Callback function passing data regarding the object to the calling application |
void *op_data | IN: User-defined pointer to data required by the application for its processing of the object |
unsigned int fields | IN: Flags specifying the fields to be retrieved to the callback op. |
Description:
H5O_VISIT2 is a recursive iteration function to visit the object obj_id and, if obj_id is a group, all objects in and below it in an HDF5 file, thus providing a mechanism for an application to perform a common set of operations across all of those objects or a dynamically selected subset. For non-recursive iteration across the members of a group, see H5L_ITERATE1.
If obj_id is a group identifier, that group serves as the root of a recursive iteration. If obj_id is a file identifier, that file’s root group serves as the root of the recursive iteration. If obj_id is any other type of object, such as a dataset or named datatype, there is no iteration.
Two parameters are used to establish the iteration: idx_type and order.
idx_type specifies the index to be used. If the links in a group have not been indexed by the index type, they will first be sorted by that index then the iteration will begin; if the links have been so indexed, the sorting step will be unnecessary, so the iteration may begin more quickly. Valid values include the following:
H5_INDEX_NAME | Alpha-numeric index on name |
H5_INDEX_CRT_ORDER | Index on creation order |
Note that the index type passed in idx_type is a best effort setting. If the application passes in a value indicating iteration in creation order and a group is encountered that was not tracked in creation order, that group will be iterated over in alpha-numeric order by name, or name order. (Name order is the native order used by the HDF5 library and is always available.)
order specifies the order in which objects are to be inspected along the index specified in idx_type. Valid values include the following:
H5_ITER_INC | Increasing order |
H5_ITER_DEC | Decreasing order |
H5_ITER_NATIVE | Fastest available order |
The prototype of the callback function op is as follows (as defined in the source code file H5Opublic.h):
typedef herr_t (*H5O_iterate1_t)(hid_t obj, const char *name, const H5O_info1_t *info, void *op_data);
The parameters of this callback function have the following values or meanings:
obj | Object that serves as root of the iteration; same value as theH5O_VISIT1 obj_id parameter |
name | Name of object, relative to o_id, being examined at current step of the iteration |
info | H5O_info1_t struct containing information regarding that object |
op_data | User-defined pointer to data required by the application in processing the object; a pass-through of the op_data pointer provided with the H5Ovisit_by_name function call |
The H5O_info1_t struct is defined in H5Opublic.h and described in the H5O_GET_INFO1 function entry.
The return values from an operator are:
- Zero causes the visit iterator to continue, returning zero when all group members have been processed.
- A positive value causes the visit iterator to immediately return that positive value, indicating short-circuit success.
- A negative value causes the visit iterator to immediately return that value, indicating failure.
The H5O_VISIT2 op_data parameter is a user-defined pointer to the data required to process objects in the course of the iteration. This pointer is passed back to each step of the iteration in the callback function’s op_data parameter.
The fields parameter contains flags to determine which fields will be retrieved by the op callback function. These flags are defined in the H5Opublic.h file:
| Flag | Purpose |
|---|---|
| H5O_INFO_BASIC | Fill in the fileno, addr, type, and rc fields |
| H5O_INFO_TIME | Fill in the atime, mtime, ctime, and btime fields |
| H5O_INFO_NUM_ATTRS | Fill in the num_attrs field |
| H5O_INFO_HDR | Fill in the hdr field |
| H5O_INFO_META_SIZE | Fill in the meta_size field |
| H5O_INFO_ALL | H5O_INFO_BASIC | H5O_INFO_TIME | H5O_INFO_NUM_ATTRS | H5O_INFO_HDR | H5O_INFO_META_SIZE |
H5L_VISIT and H5O_VISIT are companion functions: one for examining and operating on links; the other for examining and operating on the objects that those links point to. Both functions ensure that by the time the function completes successfully, every link or object below the specified point in the file has been presented to the application for whatever processing the application requires. These functions assume that the membership of the group being iterated over remains unchanged through the iteration; if any of the links in the group change during the iteration, the resulting behavior is undefined.
Programming Note for C++ Developers Using C Functions:
If a C routine that takes a function pointer as an argument is called from within C++ code, the C routine should be returned from normally.
Examples of this kind of routine include callbacks such as H5P_SET_ELINK_CB and H5P_SET_TYPE_CONV_CB and functions such as H5T_CONVERT and H5E_WALK2.
Exiting the routine in its normal fashion allows the HDF5 C library to clean up its work properly. In other words, if the C++ application jumps out of the routine back to the C++ “catch” statement, the library is not given the opportunity to close any temporary data structures that were set up when the routine was called. The C++ application should save some state as the routine is started so that any problem that occurs might be diagnosed.
Returns:
On success, returns the return value of the first operator that returns a positive value, or zero if all members were processed with no operator returning non-zero.
On failure, returns a negative value if something goes wrong within the library, or the first negative value returned by an operator.
Example:
History:
| Release | Change |
|---|---|
| 1.10.3 | C function introduced in this release. |
--- Last Modified: February 19, 2020 | 03:24 PM