Last modified: 10 April 2013
Name: H5Ovisit
Signature:
herr_t H5Ovisit( hid_t object_id, H5_index_t index_type, H5_iter_order_t order, H5O_iterate_t op, void *op_data )

Purpose:
Recursively visits all objects accessible from a specified object.

Description:
H5Ovisit is a recursive iteration function to visit the object object_id and, if object_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 H5Literate.

If object_id is a group identifier, that group serves as the root of a recursive iteration. If object_id is a file identifier, that file’s root group serves as the root of the recursive iteration. If object_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: index_type and order.

index_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 unnecesary, 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 index_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 index_type. Valid values include the following:
     H5_ITER_INC Increasing order
     H5_ITER_DEC Decreasing order
     H5_ITER_NATIVE     Fastest available order

The protoype of the callback function op is as follows (as defined in the source code file H5Opublic.h):

herr_t (*H5O_iterate_t)( hid_t o_id, const char *name, const H5O_info_t *object_info, void *op_data)

The parameters of this callback function have the following values or meanings:
     o_id Object that serves as root of the iteration; same value as the H5Ovisit object_id parameter
     name Name of object, relative to o_id, being examined at current step of the iteration
     object_info     H5O_info_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_info_t struct is defined in H5Opublic.h and described in the H5Oget_info function entry.

The return values from an operator are:

The H5Ovisit 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.
 

H5Lvisit and H5Ovisit 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.

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 H5Pset_elink_cb and H5Pset_type_conv_cb and functions such as H5Tconvert and H5Ewalk2.

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.

Parameters:
hid_t object_id IN: Identifier of the object at which the recursive iteration begins.
H5_index_t index_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_iterate_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

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.

Fortran2003 Interface: h5ovisit_f

History:
Release     Change
1.8.8 Fortran subroutine and data structure added.
1.8.0 C function introduced.