Establecido en la biblioteca de plantillas estándar de C++ (STL)

 Los conjuntos son un tipo de contenedor asociativo en el que cada elemento tiene que ser único porque el valor del elemento lo identifica. Los valores se almacenan en un orden ordenado específico, es decir, ascendente o descendente.

Sintaxis:

#include <iostream>
#include <set>
 
int main()
{
  std::set<char> a;
  a.insert('G');
  a.insert('F');
  a.insert('G');
  for(auto& str: a)
  {
    std::cout << str << ' ';
  }
  std::cout << '\n';
  return 0;
}

// CPP program to demonstrate various functions of
// Set in C++ STL
#include <iostream>
#include <iterator>
#include <set>
using namespace std;
 
int main()
{
    // empty set container
    set<int, greater<int> > s1;
 
    // insert elements in random order
    s1.insert(40);
    s1.insert(30);
    s1.insert(60);
    s1.insert(20);
    s1.insert(50);
 
    // only one 50 will be added to the set
    s1.insert(50);
    s1.insert(10);
 
    // printing set s1
    set<int, greater<int> >::iterator itr;
    cout << "\nThe set s1 is : \n";
    for (itr = s1.begin(); itr != s1.end(); itr++) {
        cout << *itr << " ";
    }
    cout << endl;
 
    // assigning the elements from s1 to s2
    set<int> s2(s1.begin(), s1.end());
 
    // print all elements of the set s2
    cout << "\nThe set s2 after assign from s1 is : \n";
    for (itr = s2.begin(); itr != s2.end(); itr++) {
        cout << *itr << " ";
    }
    cout << endl;
 
    // remove all elements up to 30 in s2
    cout << "\ns2 after removal of elements less than 30 "
            ":\n";
    s2.erase(s2.begin(), s2.find(30));
    for (itr = s2.begin(); itr != s2.end(); itr++) {
        cout << *itr << " ";
    }
 
    // remove element with value 50 in s2
    int num;
    num = s2.erase(50);
    cout << "\ns2.erase(50) : ";
    cout << num << " removed\n";
    for (itr = s2.begin(); itr != s2.end(); itr++) {
        cout << *itr << " ";
    }
 
    cout << endl;
 
    // lower bound and upper bound for set s1
    cout << "s1.lower_bound(40) : \n"
         << *s1.lower_bound(40) << endl;
    cout << "s1.upper_bound(40) : \n"
         << *s1.upper_bound(40) << endl;
 
    // lower bound and upper bound for set s2
    cout << "s2.lower_bound(40) :\n"
         << *s2.lower_bound(40) << endl;
    cout << "s2.upper_bound(40) : \n"
         << *s2.upper_bound(40) << endl;
 
    return 0;
}