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      std::is_sorted

      From cppreference.com
      <cpp‎ |algorithm
       
       
      Algorithm library
      Constrained algorithms and algorithms on ranges(C++20)
      Constrained algorithms, e.g.ranges::copy,ranges::sort, ...
      Execution policies(C++17)
      Sorting and related operations
      Partitioning operations
      Sorting operations
      is_sorted
      (C++11)

      Binary search operations
      (on partitioned ranges)
      Set operations (on sorted ranges)
      Merge operations (on sorted ranges)
      Heap operations
      Minimum/maximum operations
      (C++11)
      (C++17)
      Lexicographical comparison operations
      Permutation operations
      C library
      Numeric operations
      Operations on uninitialized memory
       
      Defined in header<algorithm>
      template<class ForwardIt>
      bool is_sorted( ForwardIt first, ForwardIt last);
      		 (1)(since C++11)
      (constexpr since C++20)
      template<class ExecutionPolicy,class ForwardIt>

      bool is_sorted( ExecutionPolicy&& policy,

                      ForwardIt first, ForwardIt last);
      		 (2)(since C++17)
      template<class ForwardIt,class Compare>
      bool is_sorted( ForwardIt first, ForwardIt last, Compare comp);
      		 (3)(since C++11)
      (constexpr since C++20)
      template<class ExecutionPolicy,class ForwardIt,class Compare>

      bool is_sorted( ExecutionPolicy&& policy,

                      ForwardIt first, ForwardIt last, Compare comp);
      		 (4)(since C++17)

      Checks if the elements in range[first, last) are sorted in non-descending order.

      1) Checks if the elements aresorted with respect tooperator<(until C++20)std::less{}(since C++20).
      3) Checks if the elements are sorted with respect tocomp.
      2,4) Same as(1,3), but executed according topolicy.
      These overloads participate in overload resolution only if all following conditions are satisfied:

      std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> istrue.

      		(until C++20)

      std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> istrue.

      		(since C++20)

      Contents

      [edit]Parameters

      first, last - the pair of iterators defining therange of elements to examine
      policy - theexecution policy to use
      comp - comparison function object (i.e. an object that satisfies the requirements ofCompare) which returns ​true if the first argument isless than (i.e. is orderedbefore) the second.

      The signature of the comparison function should be equivalent to the following:

      bool cmp(const Type1& a,const Type2& b);

      While the signature does not need to haveconst&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const)Type1 andType2 regardless ofvalue category (thus,Type1& is not allowed, nor isType1 unless forType1 a move is equivalent to a copy(since C++11)).
      The typesType1 andType2 must be such that an object of typeForwardIt can be dereferenced and then implicitly converted to both of them.​

      Type requirements
      -
      ForwardIt must meet the requirements ofLegacyForwardIterator.
      -
      Compare must meet the requirements ofCompare.

      [edit]Return value

      true if the elements in the range are sorted in non-descending order,false otherwise.

      [edit]Complexity

      Given\(\scriptsize N\)N asstd::distance(first, last):

      1,2)\(\scriptsize O(N)\)O(N) comparisons usingoperator<(until C++20)std::less{}(since C++20).
      3,4)\(\scriptsize O(N)\)O(N) applications of the comparatorcomp.

      [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

      See also the implementations inlibstdc++ andlibc++.


      is_sorted (1)
      template<class ForwardIt>bool is_sorted(ForwardIt first, ForwardIt last){returnstd::is_sorted_until(first, last)== last;}
      is_sorted (3)
      template<class ForwardIt,class Compare>bool is_sorted(ForwardIt first, ForwardIt last, Compare comp){returnstd::is_sorted_until(first, last, comp)== last;}

      [edit]Notes

      std::is_sorted returnstrue for empty ranges and ranges of length one.

      [edit]Example

      Run this code
      #include <algorithm>#include <cassert>#include <functional>#include <iterator>#include <vector> int main(){std::vector<int> v;assert(std::is_sorted(v.cbegin(), v.cend())&&"an empty range is always sorted");    v.push_back(42);assert(std::is_sorted(v.cbegin(), v.cend())&&"a range of size 1 is always sorted"); int data[]={3,1,4,1,5};assert(not std::is_sorted(std::begin(data),std::end(data))); std::sort(std::begin(data),std::end(data));assert(std::is_sorted(std::begin(data),std::end(data)));assert(not std::is_sorted(std::begin(data),std::end(data),std::greater<>{}));}

      [edit]See also

      finds the largest sorted subrange
      (function template)[edit]
      checks whether a range is sorted into ascending order
      (algorithm function object)[edit]
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