c++ sorting with custom compare function

Question

I have a vector of following type:

std::vector< std::pair< std::pair< int, int >, std::vector > >  neighbors;

I

Answer 1

Pre-C++11 solution: use an object instance as a custom comparator

struct Comparator {
    Comparator(int index) : index_(index) {}
    bool operator () (const std::pair< std::pair< int, int >, std::vector > &a,
                      const std::pair< std::pair< int, int >, std::vector > &b) 
    {
        return ( a.second[index_] > b.second[index_] );
    }

    int index_;
};

sort(neighbors.begin(), neighbors.end(), Comparator(42));

C++11+ solution: use a lambda

std::sort(neighbors.begin(), neighbors.end(), [index]
                         (const std::pair< std::pair< int, int >, std::vector > &a, 
                          const std::pair< std::pair< int, int >, std::vector > &b) 
  { 
    return ( a.second[index] > b.second[index] );
  }
);

My advice: go for a lambda if you're allowed to use C++11 features. It's probably more elegant and readable.