ITERATOR INVALIDATION

An iterator that has been invalidated must be repositioned with dict_itor_first(), dict_itor_last() or dict_itor_search() before further use. Freeing a dictionary leaves all of its iterators unusable; they may only be freed.

Trees and the skip list:

Inserting never invalidates an iterator.
Removing an element (by key, by dict_itor_remove() or by dict_clear()) invalidates iterators positioned on that element; using them is undefined. In every tree except tr_tree, removing a key whose node has two children moves the key and datum of an in-order neighbour (the successor in rb_tree and sp_tree, the successor or predecessor in hb_tree, pr_tree and wb_tree) into that node and frees the neighbour's node instead. So an iterator positioned on that neighbour is invalidated as well, and one positioned on the removed key is left on the neighbour.

Hash tables:

An insert that grows the table, an explicit resize, and dict_clear() invalidate every iterator. Inserting a key that is already present never grows the table.
hashtable: removing an element invalidates iterators positioned on it, as for the trees.
hashtable2: any removal invalidates every iterator, since it moves other elements between slots. Hash table iterators detect these invalidations: dict_itor_valid() returns false, dict_itor_key() and dict_itor_datum() return NULL, and dict_itor_next(), dict_itor_prev() and dict_itor_remove() return false.