Overriding operator< in C++ (http://coliru.stacked-crooked.com/a/dcbd4cf20810c3a4 & http://coliru.stacked-crooked.com/a/75fddbccc876ab94)

firstway.cpp

#include <string>
#include <vector>
#include <algorithm>

using namespace std;

struct One {
  string name;
  vector<string> values;
};

struct Two {
  string name;
  vector<One> one_values;

  bool operator<(const Two& other) const
  {
      return name < other.name;
  }
};

int main() {
   vector<Two> twos;
   std::sort(twos.begin(), twos.end());
}

secondway.cpp

#include <string>
#include <vector>
#include <algorithm>
 
using namespace std;
 
struct One {
  string name;
  vector<string> values;
};
 
struct Two {
  string name;
  vector<One> one_values;
};
 
bool operator<(const Two& lhs, const Two& rhs)
{
    return lhs.name < rhs.name;
}
 
int main() {
   vector<Two> twos;
   std::sort(twos.begin(), twos.end());
}