H5P_SET_MCDT_SEARCH_CB provides the means to define a callback function. An application can then use that callback to take an additional action before the default search of all committed datatypes in the destination file or to take an action that replaces the default search. This mechanism is intended to improve performance when the global search might take a long time.

H5P_SET_MCDT_SEARCH_CB allows an application to set a callback function, func, that will be invoked before searching the destination file for a matching committed datatype. The default, global search process is described in H5P_ADD_MERGE_COMMITTED_DTYPE_PATH.

The callback function must conform to the H5O_MCDT_SEARCH_CB_T prototype and will return an instruction for one of the following actions:

• Continue the search for a matching committed datatype in the destination file.
• Discontinue the search for a matching committed datatype. H5O_COPY will then apply the default behavior of creating an anonymous committed datatype.
• Abort the copy operation and exit H5O_COPY.

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 a non-negative value if successful; otherwise returns a negative value.

H5P_SET_MCDT_SEARCH_CB will fail if the object copy property list is invalid.

/* The user-defined callback function */
static H5O_mcdt_search_ret_t
mcdt_search_cb(void *_udata)
{
    H5O_mcdt_search_ret_t action = *((H5O_mcdt_search_ret_t *)_udata);

    return(action);
}

int main(void) {
    hid_t ocpypl_id = H5Pcreate(H5P_OBJECT_COPY);

    /* Enable the merging committed datatype feature. */
    H5Pset_copy_object(ocpypl_id, H5O_COPY_MERGE_COMMITTED_DTYPE_FLAG);

    /* Add a path to search for a matching committed datatype. */
    H5Padd_merge_committed_dtype_path(ocpypl_id, "/group/committed_dtypeA");

    /* 
     * Set the callback function to discontinue the global search
     * if H5Ocopy cannot find a matching committed datatype from the 
     * above suggested path.
     */
    action = H5O_MCDT_SEARCH_STOP;
    H5Pset_mcdt_search_cb(ocpypl_id, mcdt_search_cb, &action);
    H5Ocopy(...ocpypl_id...);
    ...
    ...
}