std::lexicographical_compare - cppreference.com (original) (raw)

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

1. Elements are compared using operator<.

2. Elements are compared using the given binary comparison function comp.

2,4) Same as (1,3), but executed according to policy. These overloads participate in overload resolution only if all following conditions are satisfied:

Lexicographical comparison is an 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.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Exceptions
• 5 Possible implementation
• 6 Example
• 7 Defect reports
• 8 See also

[edit] Parameters

[edit] Return value

true if the first range is lexicographically less than the second, otherwise false.

[edit] Complexity

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

1,2) At most \(\scriptsize 2\min(N_1,N_2)\)2min(1,N2) comparisons using operator<.

3,4) At most \(\scriptsize 2\min(N_1,N_2)\)2min(N1,N2) applications of the comparison function comp.

[edit] Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

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

[edit] Possible implementation

[edit] Example

#include #include #include #include   void print(const std::vector& v, auto suffix) { for (char c : v) std::cout << c << ' '; std::cout << suffix; }   int main() { std::vector v1{'a', 'b', 'c', 'd'}; std::vector 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'); }

Possible output:

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