C++ Algorithm Library - is_partitioned() Function


The C++ function std::algorithm::is_partitioned() tests whether range is partitioned or not. For empty ranges this function returns true.


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


template <class InputIterator, class UnaryPredicate>
bool is_partitioned (InputIterator first, InputIterator last, UnaryPredicate pred);


  • first − Input iterator to the initial position.

  • last − Input iterator to the final position.

  • pred − A unary function which accepts an element and returns a bool.

Return value

Returns true if range is partitioned otherwise it returns false.


Throws exception if either the pred 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_partitioned() function.

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

using namespace std;

bool is_even(int n) {
   return (n % 2 == 0);

int main(void) {
   vector<int> v = {1, 2, 3, 4, 5};
   bool result;

   result = is_partitioned(v.begin(), v.end(), is_even);

   if (result == false)
      cout << "Vector is not partitioned." << endl;

   partition(v.begin(), v.end(), is_even);

   result = is_partitioned(v.begin(), v.end(), is_even);

   if (result == true)
      cout << "Vector is paritioned." << endl;

   return 0;

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

Vector is not partitioned.
Vector is paritioned.