H5O_VISIT1 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.
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 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:
|Alpha-numeric index on name|
|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:
|Fastest available order|
The prototype of the callback function
op is as follows (as defined in the source code file
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:
|Object that serves as root of the iteration; same value as the H5O_VISIT1 |
|Name of object, relative to |
obj, being examined at current step of the iteration
|H5O_info1_t struct containing information regarding that object|
|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
|Bitbucket Server file|
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.
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
H5L_VISIT1 and H5O_VISIT1 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.