C++ Unordered_set::key_eq() Function

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The C++ std::unordered_set::key_eq() function is used to return the boolean value according to the comparison, it returns true if the equivalence occurs; otherwise, it returns false that depends on the key equivalence comparison predicate used by the unordered_set container that compares elements for equality.

The key equivalence comparison is a predicate that takes two arguments of the key type and returns a boolean value indicating whether they are to be considered equivalent.

Syntax

Following is the syntax of std::unordered_set::key_eq() function.

key_equal key_eq() const;

Parameters

This function does not accepts any parameter.

Return Value

This function returns a key equality comparison object.

Example 1

In the following example, we are going to use the unordered_set::key_eq() function and check whether the function is case-sensitive or not.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<string> uSet;
   bool case_insensitive = uSet.key_eq()("jerry","JERRY");
   cout << "uSet.key_eq() is ";
   cout << ( case_insensitive ? "case insensitive" : "case sensitive" );
   cout << endl;
   return 0;
}

Output

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

uSet.key_eq() is case sensitive

Example 2

Consider the following example, where we are going to check whether the unordered_set is similar or not using the e are using key_eq() function.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<string> uSet;
   bool equal = uSet.key_eq()("tutorialspoint","tutorialspoint");
   if(equal){
      cout<<"both elements are similar\n";
   } else{
      cout<<"dissimilar\n";
   }
   return 0;
}

Output

Following is the output of the above code −

both elements are similar

Example 3

Let's look at the following example, where we are going to use the key_eq() function and check whether the given elements are similar or not.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main() {
   unordered_set<int> uSet;
   bool	r = uSet.key_eq()( 105, 115);

   cout << "Integers are ";
   if (r == 1) {
      cout << "same";
   } else {
      cout << "not same";
   }
   return 0;
}

Output

Output of the above code is as follows −

Integers are not same