The documentation for H5Pset_efile_prefix() states:
The default behavior of the library is to search for the dataset’s external storage raw data files in the same directory as the HDF5 file which contains the dataset.
https://docs.hdfgroup.org/hdf5/v1_12/group___d_a_p_l.html#gad487f84157fd0944cbe1cbd4dea4e1b8
Examining the source code indicates the default prefix is the current directory of the program and NOT “the same directory as the HDF5 file”. The documentation appears to be incorrect here. Otherwise, this seems like a bug?
/* Prefix has to be checked for NULL / empty string again because the
* code above might have updated it.
*/
if (prefix == NULL || *prefix == '\0' || HDstrcmp(prefix, ".") == 0) {
/* filename is interpreted as relative to the current directory,
* does not need to be expanded
*/
*file_prefix = NULL;
} /* end if */
else {
if (HDstrncmp(prefix, "${ORIGIN}", HDstrlen("${ORIGIN}")) == 0) {
/* Replace ${ORIGIN} at beginning of prefix by directory of HDF5 file */
filepath_len = HDstrlen(filepath);
prefix_len = HDstrlen(prefix);
file_prefix_len = filepath_len + prefix_len - HDstrlen("${ORIGIN}") + 1;
if (NULL == (*file_prefix = (char *)H5MM_malloc(file_prefix_len)))
HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "unable to allocate buffer")
HDsnprintf(*file_prefix, file_prefix_len, "%s%s", filepath, prefix + HDstrlen("${ORIGIN}"));
} /* end if */
else {
if (NULL == (*file_prefix = (char *)H5MM_strdup(prefix)))
HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
} /* end else */
} /* end else */
done:
FUNC_LEAVE_NOAPI(ret_value)
} /* H5D__build_file_prefix() */