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Recursively visits all links starting from a specified group


H5L_VISIT_BY_NAME2 ( loc_id, group_name, idx_type, order, op, op_data, lapl_id )


herr_t H5Lvisit_by_name2 ( hid_t loc_id, const char *group_name, H5_index_t idx_type,
    H5_iter_order_t order, H5L_iterate2_t op, void *op_data, hid_t lapl_id )

hid_t loc_idIN: Location identifier; may be a file, group, dataset, named datatype or attribute identifier
const char *nameIN: Name of the group, generally relative to loc_id, that will serve as root of the iteration
H5_index_t idx_typeIN: Type of index; valid values include: 
H5_iter_order_t order    IN: Order in which index is traversed; valid values include: 
H5L_iterate2_t opIN: Callback function passing data regarding the link to the calling application
void *op_dataIN: User-defined pointer to data required by the application for its processing of the link
hid_t lapl_idIN: Link access property list identifier


H5L_VISIT_BY_NAME2 is a recursive iteration function to visit all links in and below a group in an HDF5 file, thus providing a mechanism for an application to perform a common set of operations across all of those links or a dynamically selected subset. For non-recursive iteration across the members of a group, see   H5L_ITERATE2  .

The group serving as the root of the iteration is specified by the loc_id / group_name parameter pair. loc_id specifies a file or group; group_name specifies either a group in the file (with an absolute name based in the file’s root group) or a group relative to loc_id. If loc_id fully specifies the group that is to serve as the root of the iteration, group_name should be '.' (a dot). (Note that when loc_id fully specifies the the group that is to serve as the root of the iteration, the user may wish to consider using  H5L_VISIT2 instead of H5L_VISIT_BY_NAME2.)

Two parameters are used to establish the iteration: idx_type and order.

idx_type specifies the index to be used. If the links 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_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 op callback function, the related H5L_info2_t struct, and the effect that the callback function’s return value has on the application are described in H5L_VISIT2.

The H5L_VISIT_BY_NAME2 op_data parameter is a user-defined pointer to the data required to process links 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.

lapl_id is a link access property list. In the general case, when default link access properties are acceptable, this can be passed in as H5P_DEFAULT. An example of a situation that requires a non-default link access property list is when the link is an external link; an external link may require that a link prefix be set in a link access property list (see H5P_SET_ELINK_PREFIX).

H5L_VISIT_BY_NAME2 and H5O_VISIT_BY_NAME2 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 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.


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.


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Release    Change
1.12.0Function was introduced in this release.

--- Last Modified: March 12, 2020 | 02:26 PM