C++ Unordered_set::operator!=() Function

The C++ std::unordered_set::operator!=() function is used to check whether two unordered_sets are equal or not. if both unordered_set are not equal returns true otherwise false.

This function checks the size of the unordered_set, if the size is same then it starts comparing the elements of the unordered_set and this function stop comparing when it find the first mismatch.

Syntax

Following is the syntax of non member std::unordered_set::operator!= function.

bool operator!= (const unordered_set<Key,Hash,Pred,Alloc>& lhs, 
                 const unordered_set<Key,Hash,Pred,Alloc>& rhs);

Parameters

• first − It indicates the First unordered_set.
• second − It indicates the Second unordered_set.

Return value

This function returns true if both unordered_set are not equal otherwise false.

Example 1

Let's look at the following example, where we are going to demonstrate the usage of the unordered_set::operator!=() function.

#include <iostream>
#include <unordered_set>
using namespace std;
int main(void) {
   unordered_set<int> uSet1;
   unordered_set<int> uSet2;
   uSet1.emplace(1);
   if (uSet1 != uSet2)
      cout << "Both unordered_sets are not equal" << endl;
   //copy element of uSet1 into uSet2
   uSet1 = uSet2;
   if (!(uSet1 != uSet2))
      cout << "Both unordered_sets are equal" << endl;
   return 0;
}

Output

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

Both unordered_sets are not equal
Both unordered_sets are equal

Example 2

In the following example, we are going to create a unordered_set of same type with different elements and applying the operator!=() function to compare whether they are equal or not.

#include <iostream>
#include <unordered_set>
using namespace std;
int main(void) {
   unordered_set<int> uSet1 = { 1, 2, 3, 4, 8 };
   unordered_set<int> uSet2 = { 2, 3, 4, 5, 3 };
   if (uSet1 != uSet2)
      cout << "Both unordered_sets are not equal" << endl;
   if (!(uSet1 != uSet2))
      cout << "Both unordered_sets are equal" << endl;
   return 0;
}

Output

If we run the above code it will generate the following output −

Both unordered_sets are not equal

Example 3

Following is the example, where we are going to display the elements of both unordered_sets, if they are not equal orelse elements of one unordered_set is displayed.

#include <iostream>
#include <unordered_set>
using namespace std;
int main(void) {
   unordered_set<string> uSet1 = {"aman", "akash", "vivek", "Rahul"};
   unordered_set<string> uSet2 = {"Vivek", "Alok", "Sakshi", "Akash"};
   if (uSet1 != uSet2) {
      cout<<"elements of uSet1"<<endl;
      for(auto & it: uSet1){
         cout<<it<<endl;
      }
      cout<<endl;
      cout<<"elements of uSet2"<<endl;
      for(auto & it: uSet2){
         cout<<it<<endl;
      }
   }
   if (!(uSet1 != uSet2)){
      cout << " elements of both unordered_sets are equal" << endl;
      for(auto& it: uSet1){
         cout<<it<<endl;
      }
   }
   return 0;
}

Output

Following is the output of the above code −

elements of uSet1
vivek
Rahul
akash
aman

elements of uSet2
Akash
Sakshi
Alok
Vivek

Example 4

Consider the following example, where we are going to use the using the operator!=() function to check whether the size of unordered_sets effects or not.

#include <iostream>
#include <unordered_set>
using namespace std;
int main(void) {
   unordered_set<int> uSet1 = {1, 2, 3, 4};
   unordered_set<int> uSet2 = {1, 2, 3};
   cout<<"Is both unorded_set container not equal: ";
   if(uSet1!=uSet2)
      cout<<"not equal!"<<endl;
   else
      cout<<"equal"<<endl;
   return 0;
}

Output

Output of the above code is as follows −

Is both unorded_set container not equal: not equal!