C++ Algorithm Library - is_sorted() Function


The C++ function std::algorithm::is_sorted() tests whether range is sorted or not. It uses binary function for comparision.


Following is the declaration for std::algorithm::is_sorted() function form std::algorithm header.


template <class ForwardIterator, class Compare>
bool is_sorted (ForwardIterator first, ForwardIterator last, Compare comp);


  • first − Forward iterator to the initial position.

  • last − Forward iterator to the final position.

  • comp − A binary function which accepts two arguments and returns bool.

Return value

Returns true if range is sorted otherwise returns false.


Throws exception if either the binary function or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

Time complexity



The following example shows the usage of std::algorithm::is_sorted() function.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

bool ignore_case(char a, char b) {
   return (tolower(a) == tolower(b));

int main(void) {
   vector<char> v = {'A', 'b', 'C', 'd', 'E'};
   bool result;

   result = is_sorted(v.begin(), v.end());

   if (result == false)
      cout << "Vector elements are not sorted in ascending order." << endl;

   result = is_sorted(v.begin(), v.end(), ignore_case);

   if (result == true)
      cout << "Vector elements are sorted in ascending order." << endl;

   return 0;

Let us compile and run the above program, this will produce the following result −

Vector elements are not sorted in ascending order.
Vector elements are sorted in ascending order.
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