std::experimental::ranges::lexicographical_compare

 

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Technical specifications

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Algorithms library

Non-modifying sequence operations
all_ofany_ofnone_of countcount_if	findfind_iffind_if_not find_end find_first_of	adjacent_find search search_n mismatch	equal for_each lexicographical_compare
Modifying sequence operations
copycopy_if copy_n copy_backward move move_backward	fill fill_n generate generate_n swap_ranges shuffle transform	removeremove_if replacereplace_if reverse rotate unique	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy
Partitioning operations
is_partitioned partition_point	partition partition_copy	stable_partition
Sorting operations
is_sorted is_sorted_until	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	includes	set_difference set_intersection	set_symmetric_difference set_union
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is_heap is_heap_until	make_heap sort_heap	push_heap pop_heap
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max max_element	min min_element	minmax minmax_element
Permutations
is_permutation	next_permutation	prev_permutation

 

Defined in header <experimental/ranges/algorithm>
template< InputIterator I1, Sentinel<I1> S1, InputIterator I2, Sentinel<I2> S2,           class Proj1 = ranges::identity, class Proj2 = ranges::identity,           class Comp = ranges::less<> >   requires IndirectStrictWeakOrder<Comp, projected<I1, Proj1>, projected<I2, Proj2>> bool lexicographical_compare(I1 first1, S1 last1, I2 first2, S2 last2,                              Comp comp = Comp{},                              Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{});	(1)	(ranges TS)
template< InputRange R1, InputRange R2,           class Proj1 = ranges::identity, class Proj2 = ranges::identity,           class Comp = ranges::less<> >   requires IndirectStrictWeakOrder<Comp, projected<ranges::iterator_t<R1>, Proj1>,                                          projected<ranges::iterator_t<R2>, Proj2>> bool lexicographical_compare(R1&& r1, R2&& r2, Comp comp = Comp{},                              Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{});	(2)	(ranges TS)

1) Checks if the first range [first1, last1) is lexicographically less than the second range [first2, last2). Elements are compared using the given binary comparison function comp, after being projected with proj1 and proj2 respectively.

2) Same as (1), but uses r1 as the first source range and r2 as the second source range, as if using ranges::begin(r1) as first1, ranges::end(r1) as last1, ranges::begin(r2) as first2, and ranges::end(r2) as last2.

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 ranges are lexicographically equal.

Parameters

first1, last1	-	the first range of elements to examine
r1	-	the first range of elements to examine
first2, last2	-	the second range of elements to examine
r2	-	the second range of elements to examine
comp	-	comparison function to apply to the projected elements
proj1	-	projection to apply to the elements in the first range
proj2	-	projection to apply to the elements in the second range

Return value

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

Complexity

At most 2·min(N1, N2) applications of the comparison operation, where N1 = last1 - first1 and N2 = last2 - first2.

Possible implementation

template< InputIterator I1, Sentinel<I1> S1, InputIterator I2, Sentinel<I2> S2, class Proj1 = ranges::identity, class Proj2 = ranges::identity, class Comp = ranges::less<> > requires IndirectStrictWeakOrder<Comp, projected<I1, Proj1>, projected<I2, Proj2>> bool lexicographical_compare(I1 first1, S1 last1, I2 first2, S2 last2, Comp comp = Comp{}, Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{}) { for ( ; (first1 != last1) && (first2 != last2); (void) ++first1, (void) ++first2 ) { if (ranges::invoke(comp, ranges::invoke(proj1, *first1), ranges::invoke(proj2, *first2))) return true; if (ranges::invoke(comp, ranges::invoke(proj2, *first2), ranges::invoke(proj1, *first1))) return false; } return (first1 == last1) && (first2 != last2); }

See also

lexicographical_compare	returns true if one range is lexicographically less than another (function template)
equal	determines if two sets of elements are the same (function template)