C++ set for user define data type

Here we will see how we can make a set for user defined datatypes. The Set is present in C++ STL. This is a special type of data structure, it can store data in sorted order, and does not support duplicate entry. We can use set for any type of data, but here we will see how we can also use set for userdefined datatypes.

To use user-defined datatypes into stack, we have to override < operator, that can compare two values of that type. If this is not present, it cannot compare two objects, so the set cannot store data in sorted order, so will raise an exception.

Example

#include <iostream>
#include<set>
using namespace std;
class Student {
   int id, marks;
   public:
   Student(int id, int marks){
      this->id = id;
      this->marks = marks;
   }
   bool operator <(const Student& st) const{ //sort using id,
      return (this->id < st.id);
   } void display() const{
      cout << "(" << id << ", " << marks << ")\n";
   }
};
main() {
   Student s1(5, 70), s2(3, 86), s3(2, 91), s4(2, 60), s5(1, 78), s6(6, 53), s7(4, 59);
   //the set will not consider duplicate id
   set<Student> st_set;
   st_set.insert(s1);
   st_set.insert(s2);
   st_set.insert(s3);
   st_set.insert(s4);
   st_set.insert(s5);
   st_set.insert(s6);
   st_set.insert(s7);
   set<Student>::iterator it;
   for(it = st_set.begin(); it != st_set.end(); it++){
      it->display();
   }
}

Output

(1, 78)
(2, 91)
(3, 86)
(4, 59)
(5, 70)
(6, 53)