C++ Unordered_multimap Library - operator!=() Function


The C++ function std::unordered_multimap::operator!=() tests whether two unordered_multimaps are equal or not.


Following is the declaration for std::unordered_multimap::operator!=() function form std::unordered_map() header.


template <class Key, class T, class Hash, class Pred, class Alloc>
bool operator!=(const unordered_multimap<Key,T,Hash,Pred,Alloc>& first,
                const unordered_multimap<Key,T,Hash,Pred,Alloc>& second);


  • first − First unordered_multimap object.

  • second − Second unordered_multimap object.

Return value

Returns true if both unordered_multimaps not are equal otherwise false.

Time complexity

Linear i.e. O(n) in average case.

Quadratic i.e. O(n2) in worst case.


The following example shows the usage of std::unordered_multimap::operator!=() function.

#include <iostream>
#include <unordered_map>

using namespace std;

int main(void) {
   unordered_multimap<char, int> umm1;
   unordered_multimap<char, int> umm2;

   umm1.emplace('a', 1);

   if (umm1 != umm2)
      cout << "Both unordered_multimaps are not equal." << endl;

   umm1 = umm2;

   if (!(umm1 != umm2))
      cout << "Both unordered_multimaps are equal." << endl;

   return 0;

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

Both unordered_multimaps are not equal.
Both unordered_multimaps are equal.