It might not be clear from the example, that
strcspn('abcdhelloabcd', 'abcd', -9, -5) == 4
because it's only evaluating 'hell' which doesn't contain any mask, so returns strlen('hell').
It might not be clear from the example, that
strcspn('abcdhelloabcd', 'abcd', -9, -5) == 4
because it's only evaluating 'hell' which doesn't contain any mask, so returns strlen('hell').