Checks if the first range[first1, last1) is lexicographicallyless than the second range[first2, last2).

Lexicographical comparison is an operation with the following properties:

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

The function-like entities described on this page arealgorithm function objects (informally known asniebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible toargument-dependent lookup.
• When any of them are found bynormal unqualified lookup as the name to the left of the function-call operator,argument-dependent lookup is inhibited.

[edit]Parameters

[edit]Return value

true if the first range is lexicographicallyless than the second.

[edit]Complexity

At most2·min(N1, N2) applications of the comparison and corresponding projections, whereN1=ranges::distance(first1, last1) andN2=ranges::distance(first2, last2).

[edit]Possible implementation

struct lexicographical_compare_fn{template<std::input_iterator I1,std::sentinel_for<I1> S1,std::input_iterator I2,std::sentinel_for<I2> S2,class Proj1=std::identity,class Proj2=std::identity,std::indirect_strict_weak_order<                 std::projected<I1, Proj1>,                 std::projected<I2, Proj2>> Comp=ranges::less>constexprbool operator()(I1 first1, S1 last1, I2 first2, S2 last2,                              Comp comp={}, Proj1 proj1={}, Proj2 proj2={})const{for(;(first1!= last1)&&(first2!= last2);++first1,(void)++first2){if(std::invoke(comp,std::invoke(proj1,*first1),std::invoke(proj2,*first2)))returntrue; if(std::invoke(comp,std::invoke(proj2,*first2),std::invoke(proj1,*first1)))returnfalse;}return(first1== last1)&&(first2!= last2);} template<ranges::input_range R1,ranges::input_range R2,class Proj1=std::identity,class Proj2=std::identity,std::indirect_strict_weak_order<                 std::projected<ranges::iterator_t<R1>, Proj1>,                 std::projected<ranges::iterator_t<R2>, Proj2>> Comp=ranges::less>constexprbool operator()(R1&& r1, R2&& r2, Comp comp={},                              Proj1 proj1={}, Proj2 proj2={})const{return(*this)(ranges::begin(r1),ranges::end(r1),ranges::begin(r2),ranges::end(r2),std::ref(comp),std::ref(proj1),std::ref(proj2));}}; inlineconstexpr lexicographical_compare_fn lexicographical_compare;

[edit]Example

#include <algorithm>#include <iostream>#include <iterator>#include <random>#include <vector> int main(){std::vector<char> v1{'a','b','c','d'};std::vector<char> v2{'a','b','c','d'}; namespace ranges= std::ranges;auto os=std::ostream_iterator<char>(std::cout," "); std::mt19937 g{std::random_device{}()};while(not ranges::lexicographical_compare(v1, v2)){ranges::copy(v1, os);std::cout<<">= ";ranges::copy(v2, os);std::cout<<'\n'; ranges::shuffle(v1, g);ranges::shuffle(v2, g);} ranges::copy(v1, os);std::cout<<"<  ";ranges::copy(v2, os);std::cout<<'\n';}

a b c d >= a b c dd a b c >= c b d ab d a c >= a d c ba c d b <  c d a b

[edit]See also

• In other languages

• Deutsch
• Español
• Français
• Italiano
• 日本語
• Português
• Русский
• 中文