#include <set>
#include <iostream>
using namespace std;
set<string> yourSet;

    const string& add_new_entry(const string& str)
    {
        set<string>::iterator iter = yourSet.find(str);
        if (iter == yourSet.end())
          return *yourSet.insert(str).first;
        return *iter;
    }

int main()
{
    cout << add_new_entry("abc") << endl;
}