C++ unordered_multimap::operator==() Function

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

This function will work when the both the multimaps have the same data type, If we try to compare the unordered_multimaps with different data types, then it will displays an error.

Syntax

Following is the syntax of std::unordered_multimap::operator== function.

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

Parameters

  • first − First unordered_multimap object.
  • second − Second unordered_multimap object.

Return value

This function returns true if both unordered_multimap are equal otherwise false.

Example 1

In the following example, let's see the usage of unordered_multimap::operator== function.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_map<char, int> umm1;
   unordered_map<char, int> umm2;
   if (umm1 == umm2)
      cout << "Both unordered_maps are equal" << endl;
   umm1.emplace('a', 1);
   if (!(umm1 == umm2))
      cout << "Both unordered_maps are not equal" << endl;
   return 0;
}

Output

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

Both unordered_multimaps are equal
Both unordered_multimaps are not equal

Example 2

Let's the following example, where we are going to use the operator==() function on the multimaps stored with same elements in different order.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm1 = {{'C', 3}, {'A', 5}, {'B', 2}, {'A', 1}, {'D', 4}};
   unordered_multimap<char, int> umm2 = {{'D', 4}, {'A', 5}, {'A', 1}, {'B', 2}, {'C', 3}};
   if (umm1 == umm2)
      cout << "Both unordered_multimaps are equal" << endl;
   else
      cout << "Bothe are not equal"<<endl;
   return 0;
}

Output

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

Both unordered_multimaps are equal

Example 3

Consider the another scenario, where we are going to use the operator==() function on the multimaps of the same type with different elements.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm1 = {{'E', 5}, {'f', 6}, {'g', 7}, {'H', 8}};
   unordered_multimap<char, int> umm2 = {{'D', 4}, {'A', 1}, {'B', 2}, {'C', 3}};
   if (umm1 == umm2)
      cout << "Both unordered_multimaps are equal" << endl;
   if (!(umm1 == umm2))
      cout << "Both unordered_multimaps are not equal" << endl;
   return 0;
}

Output

Following is the output of the above code −

Both unordered_multimaps are not equal

Example 4

Following is the example, where we are going to create a multimap that stores different data types and applying the operator==() function to check whether both are equal or not.

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm1 = {{'E', 5}, {'f', 6}, {'g', 7}, {'H', 8}};
   unordered_multimap<int, int> umm2 = {{1, 4}, {2, 1}, {2, 2}, {4, 3}};
   if (umm1 == umm2)
      cout << "Both unordered_multimaps are equal" << endl;
   if (!(umm1 == umm2))
      cout << "Both unordered_multimaps are not equal" << endl;
   return 0;
}

Output

Output of the above code is as follows −

ERROR!
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