std::lexicographical_compare

From Cppreference

Checks if the first range ​[first1, last1)​ is lexicographically less than the second range ​[first2, last2)​. The first version uses ​operator<​ to compare the elements, the second version uses the given comparison function comp.

Lexicographical comparison is a operation with the following properties:

• Two ranges are compared element by element.
• The first mismatching element defines which range is lexicographically less or greater than the other.
• If one range is a prefix of another, the shorter range is lexicographically less than the other.
• If two ranges have equivalent elements and are of the same length, then the ranges are lexicographically equal.
• An empty range is lexicographically less than any non-empty range.
• Two empty range- are lexicographically equal.

Parameters

Return value

​true​ if the first range is lexicographically less than the second.

Complexity

At most ​2 * min(count1, count2)​ applications of the comparison operation, where ​count1 = std::distance(first1, last1)​ and ​count2 = std::distance(first2, last2)​.

Equivalent function

​template<class InputIterator1, class InputIterator2>
bool lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
                             InputIterator2 first2, InputIterator2 last2)
{
    for ( ; (first1 != last1) && (first2 != last2) ; first1++, first2++ ) {
        if (*first1 < *first2) return true;
        if (*first2 < *first1) return false;
    }
    return (first1 == last1) && (first2 != last2);
}​

​template<class InputIterator1, class InputIterator2, class Compare>
bool lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
                             InputIterator2 first2, InputIterator2 last2,
                             Compare comp)
{
    for ( ; (first1 != last1) && (first2 != last2) ; first1++, first2++ ) {
        if (comp(*first1, *first2)) return true;
        if (comp(*first2, *first1)) return false;
    }
    return (first1 == last1) && (first2 != last2);
}​

Example