The versioned H5Oget_info functions (H5Oget_info1 and H5Oget_info2) were added in 1.10.3, and H5Oget_info was replaced by a macro to invoke H5Oget_info1 or H5Oget_info2. However, this broke compatibility and caused problems for users because there was no longer a function H5Oget_info.  In 1.10.4 and subsequent 1.10.x versions the macro was removed, H5Oget_info1 was deprecated, and H5Oget_info was resurrected as a function. H5Oget_info2 remained as a function, but is not a versioned alternative to the original H5Oget_info. The same is true for H5Oget_info_by name, H5Oget_info_by_idx, H5Ovisit, and H5Ovisit_by_name. The "version 2 " versions functions were introduced added to improve performance.

The unversioned originals and version 2 of those functions exist in 1.10 because having released them in 1.10.3, it would break compatibility to remove them, so the original and version 2 functions remained in the source but without any macro to map to one or the other.  Therefore, version 2 functions are available, but only when invoked directly.

In 1.12 there is a version 3 of all 5 functions which uses version 2 H5Oinfo2_t or H5Oiterate2_t structures.  Both versions 1 and 2 are deprecated and macros replace the unversioned functions, mapping to version 1 for 18 and 110 default apis and to version 3 for 112 default api.  Version 2 is available, but will only be invoked if invoked directly.