C++ Unordered_map::key_eq() Function

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The C++ function std::unordered_map::key_eq() is used to return the boolean value according to the comparison. It returns true if the equivalence occurs; otherwise, it returns false.

The key equivalence comparison is a predicate that takes two arguments of the key type and returns a bool value indicating whether they are to be considered equivalent. Default predicate is equal_to<key_type>, which returns the same as applying the equal-to operator (==) to the arguments.

Syntax

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

key_equal key_eq() const;

Parameters

This function does not accept any parameter.

Return value

This function returns a boolean value true if the equivalence occurs; otherwise, it returns false.

Example 1

Let's look at the following example, where we are going to demonstrate the usage of the key_eq() function.

#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;
int main () {
   unordered_map<string,string> um;
   bool case_insensitive = um.key_eq()("jerry","JERRY");
   cout << "mymap.key_eq() is ";
   cout << ( case_insensitive ? "case insensitive" : "case sensitive" );
   cout << endl;
   return 0;
}

Output

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

mymap.key_eq() is case sensitive

Example 2

In the following example, we are using key_eq() function to check both key of unordered_map is similar or not.

#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;
int main () {
   unordered_map<string,string> um;
   bool equal = um.key_eq()("tutorialspoint","TUTORIALSPOAINT");
   if(equal){
      cout<<"both are similar\n";
   }
   else{
      cout<<"dissimilar\n";
   }
   return 0;
}

Output

Following is the output of the above code −

dissimilar

Example 3

Consider the following example, where we are creating an unordered_map that takes integer value and applying the key_eq() function to check both key of unordered_map is similar or not.

#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;
int main () {
   unordered_map<int,int> um;
   bool equal = um.key_eq()(105, 105);
   if(equal)
      cout<<"similar\n";
   else
      cout<<"dissimilar";
   return 0;
}

Output

Output of the above code is as follows −

similar