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.

[edit]Parameters

[edit]Return value

true if the first range is lexicographicallyless than the second, otherwisefalse.

[edit]Complexity

Given\(\scriptsize N_1\)N1 asstd::distance(first1, last1) and\(\scriptsize N_2\)N2 asstd::distance(first2, last2):

[edit]Exceptions

The overloads with a template parameter namedExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard policies,std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory,std::bad_alloc is thrown.

[edit]Possible implementation

template<class InputIt1,class InputIt2>bool lexicographical_compare(InputIt1 first1, InputIt1 last1,                             InputIt2 first2, InputIt2 last2){for(;(first1!= last1)&&(first2!= last2);++first1,(void)++first2){if(*first1<*first2)returntrue;if(*first2<*first1)returnfalse;} return(first1== last1)&&(first2!= last2);}

template<class InputIt1,class InputIt2,class Compare>bool lexicographical_compare(InputIt1 first1, InputIt1 last1,                             InputIt2 first2, InputIt2 last2, Compare comp){for(;(first1!= last1)&&(first2!= last2);++first1,(void)++first2){if(comp(*first1,*first2))returntrue;if(comp(*first2,*first1))returnfalse;} return(first1== last1)&&(first2!= last2);}

[edit]Example

#include <algorithm>#include <iostream>#include <random>#include <vector> void print(conststd::vector<char>& v,auto suffix){for(char c: v)std::cout<< c<<' ';std::cout<< suffix;} int main(){std::vector<char> v1{'a','b','c','d'};std::vector<char> v2{'a','b','c','d'}; for(std::mt19937 g{std::random_device{}()};!std::lexicographical_compare(v1.begin(), v1.end(),                                       v2.begin(), v2.end());){        print(v1,">= ");        print(v2,'\n'); std::shuffle(v1.begin(), v1.end(), g);std::shuffle(v2.begin(), v2.end(), g);}     print(v1,"<  ");    print(v2,'\n');}

a b c d >= a b c d d a b c >= c b d a b d a c >= a d c b a c d b <  c d a b

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]See also

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