C++ Algorithm Library - is_heap() Function


The C++ function std::algorithm::is_heap() tests whether given sequence is max heap or not. It uses binary function for comparison.


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


template <class RandomAccessIterator, class Compare>
bool is_heap(RandomAccessIterator first,RandomAccessIterator last,Compare comp);


  • first − Random access iterator to the initial position.

  • last − Random access iterator to the final position.

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

Return value

Returns true if given sequence is max heap otherwise returns false.


Throws exception if either the element comparison 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_heap() 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 = {'E', 'd', 'C', 'b', 'A'};
   bool result;

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

   if (result == false)
      cout << "Given sequence is not a max heap." << endl;

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

   if (result == true)
      cout << "Given sequence is a max heap." << endl;

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

Given sequence is not a max heap.
Given sequence is a max heap.