lower_bound == upper_bound

Question

What does lower_bound mean. If I had to guess I would answer that this function returns the iterator at the last element that is less than the value asked for. But I see tha

Answer 1

lower_bound, upper_bound and equal_range are functions which perform binary search in a sorted sequence. The need for three functions comes from the fact that elements may be repeated in the sequence:

1, 2, 3, 4, 4, 4, 5, 6, 7

In this case, when searching for the value 4, lower_bound will return an iterator pointing to the first of the three elements with value 4, upper_bound will return an iterator pointing to the element with value 5, and equal_range will return a pair containing these two iterators.