data to lookup
the function used to compare iterators in the sequence
user data passed to @iter_cmp
an #GSequenceIter pointing to the position of the first item found equal to @data according to @cmp_func and @cmp_data, or %NULL if no such item exists
2.28
Like g_sequence_lookup(), but uses a #GSequenceIterCompareFunc instead of a #GCompareDataFunc as the compare function.
@iter_cmp is called with two iterators pointing into @seq. It should return 0 if the iterators are equal, a negative value if the first iterator comes before the second, and a positive value if the second iterator comes before the first.
This function will fail if the data contained in the sequence is unsorted.