How to create an unordered_set of user defined class or struct in C++?

In this tutorial, we will be discussing a program to understand how to create an unordered set of user defined class or struct in C++.

For this we will create a structure type and then compare two structure types with the function defined by the user to store the hash function.

Example

#include <bits/stdc++.h>
using namespace std;
//defined structure
struct Test {
   int id;
   bool operator==(const Test& t) const{
      return (this->id == t.id);
   }
};
//defined class for hash function
class MyHashFunction {
   public:
      size_t operator()(const Test& t) const{
         return t.id;
   }
};
int main(){
   Test t1 = { 110 }, t2 = { 102 }, t3 = { 101 }, t4 = { 115 };
   //defining unordered set
   unordered_set<Test, MyHashFunction> us;
   us.insert(t1);
   us.insert(t2);
   us.insert(t3);
   us.insert(t4);
   for (auto e : us) {
      cout << e.id << " ";
   }
   return 0;
}

Output

115 101 110 102