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H5O_VISIT3

Recursively visits all objects accessible from a specified object

Procedure:

H5O_VISIT3 ( obj_id, idx_type, order, op, op_data, fields )

Signature:

herr_t H5Ovisit3 ( hid_t obj_id, H5_index_t idx_type, H5_iter_order_t order, H5O_iterate2_t op, 
           void *op_data, unsigned fields )

SUBROUTINE h5ovisit_f(object_id, index_type, order, op, op_data, &
            return_value, hdferr)
    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

Parameters:
hid_t obj_idIN: 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_typeIN: 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_iterate2_t opIN: Callback function passing data regarding the object to the calling application
void *op_dataIN: User-defined pointer to data required by the application for its processing of the object
unsigned fieldsIN: Flags specifying the fields to be retrieved to the callback op.

Description:

H5O_VISIT3 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_ITERATE2 .

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_NAMEAlpha-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_INCIncreasing order
H5_ITER_DECDecreasing 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_iterate2_t)(hid_t obj, const char *name, const H5O_info2_t *info, void *op_data);

The parameters of this callback function have the following values or meanings:

objObject that serves as root of the iteration; same value as the H5Ovisit object_id parameter
nameName of object, relative to o_id, being examined at current step of the iteration
info    H5O_info2_t struct containing information regarding that object
op_dataUser-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_info2_t struct is defined in H5Opublic.h as follows:

src / H5Opublic.h [129:141]  hdf5_1_12  HDFFV/hdf5
    } mesg;
} H5O_hdr_info_t;

/* Data model information struct for objects */
/* (For H5Oget_info / H5Oget_info_by_name / H5Oget_info_by_idx version 3) */
typedef struct H5O_info2_t {
    unsigned long fileno;    /* File number that object is located in */
    H5O_token_t   token;     /* Token representing the object        */
    H5O_type_t    type;      /* Basic object type (group, dataset, etc.) */
    unsigned      rc;        /* Reference count of object            */
    time_t        atime;     /* Access time                          */
    time_t        mtime;     /* Modification time                    */
    time_t        ctime;     /* Change time                          */

H5O_token_t is defined in H5public.h as follows:

src / H5public.h [337:341]  hdf5_1_12  HDFFV/hdf5
/*
 * Allocation statistics info struct
 */
typedef struct H5_alloc_stats_t {
    unsigned long long total_alloc_bytes;        /* Running count of total # of bytes allocated */

The  H5O_type_t  enum indicates the object type and is defined (in  H5Opublic.h) as follows:

src / H5Opublic.h [101:109]  hdf5_1_12  HDFFV/hdf5
/* Public Typedefs */
/*******************/

/* Types of objects in file */
typedef enum H5O_type_t {
    H5O_TYPE_UNKNOWN = -1,   /* Unknown object type		*/
    H5O_TYPE_GROUP,          /* Object is a group		*/
    H5O_TYPE_DATASET,        /* Object is a dataset		*/
    H5O_TYPE_NAMED_DATATYPE, /* Object is a named data type	*/

Note that obj_id refers only to the types specified by H5O_type_t.

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_VISIT3 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:

FlagPurpose
H5O_INFO_BASICFill in the fileno, addr, type, and rc fields
H5O_INFO_TIMEFill in the atime, mtime, ctime, and btime fields
H5O_INFO_NUM_ATTRSFill in the num_attrs field
H5O_INFO_HDRFill in the hdr field
H5O_INFO_META_SIZEFill in the meta_size field
H5O_INFO_ALLH5O_INFO_BASIC | H5O_INFO_TIME | H5O_INFO_NUM_ATTRS | H5O_INFO_HDR | H5O_INFO_META_SIZE

H5L_VISIT2 and H5O_VISIT3 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
1.12.0The function was introduced

--- Last Modified: October 23, 2020 | 02:58 PM