C++: What is the difference between std::binary_search and std::lower_bound?

binary_search — checks existence. lower_bound — finds position.

std::binary_search:

• Returns bool.
• Checks if element exists.

1std::vector<int> v = {1, 3, 5, 7, 9};
2bool found = std::binary_search(v.begin(), v.end(), 5);
3// true

std::lower_bound:

• Returns iterator.
• First element >= value.

1auto it = std::lower_bound(v.begin(), v.end(), 5);
2// Points to 5
3
4auto it2 = std::lower_bound(v.begin(), v.end(), 6);
5// Points to 7 (first >= 6)

upper_bound:

• First element > value.

equal_range:

• Pair of lower/upper bounds.