unordered_set == operator in C++ STL

The ‘==’ is an operator in C++ STL performs equality comparison operation between two unordered sets and unordered_set::operator== is the corresponding operator function for the same.

Syntax:

(unordered_set &uset1 == unordered_set &uset2)

Parameters: This operator function takes reference of two unordered sets uset1 and uset2 as parameters which are to be compared.

Return Value: This method returns a boolean result value after comparing the two sets. The comparison procedure is as follows:

  • Firstly their sizes are compared .
  • Then each element in ust1 is looked for in ust2

If both the conditions are satisfied true value is returned and at any point if a condition is not satisfied, false value is returned.

Below program illustrates unordered_set::operator== in C++.

Program:

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#include <iostream>
#include <unordered_set>
using namespace std;
  
int main()
{
    // Initilize three unordered sets
    unordered_set<int>
        sample1 = { 10, 20, 30, 40, 50 };
    unordered_set<int>
        sample2 = { 10, 30, 50, 40, 20 };
    unordered_set<int>
        sample3 = { 10, 20, 30, 50, 60 };
  
    // Compare sample1 and sample2
    if (sample1 == sample2) {
  
        cout << "sample1 and "
             << "sample2 are equal."
             << endl;
    }
    else {
  
        cout << "sample1 and "
             << "sample2 are not equal."
             << endl;
    }
  
    // Compare sample2 and sample3
    if (sample2 == sample3) {
  
        cout << "sample2 and "
             << "sample3 are equal."
             << endl;
    }
    else {
  
        cout << "sample2 and "
             << "sample3 are not equal."
             << endl;
    }
  
    return 0;
}

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Output:

sample1 and sample2 are equal.
sample2 and sample3 are not equal.


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