template <typename K, typename V>
 int comparePairs(const void* left, const void* right){
        if((((pair<K,V>*)left)->first) <= (((pair<K,V>*)right)->first))
            return 1;
        else
            return -1;
    }

vector<pair<K,V>> items;

std::sort(items.begin(), items.end(), comparePairs<K,V>);

std::vector<pair<K,V>> items;
std::sort(items.begin(), items.end());

template <typename K, typename V>
bool comparePairs(const std::pair<K,V>& lhs, const std::pair<K,V>& rhs)
{
  return lhs.first < rhs.first;
}

template< class RandomIt, class Compare >
void sort( RandomIt first, RandomIt last, Compare comp );

std::sort(std::begin(container), std::end(container),
          [] (const auto& lhs, const auto& rhs) {
    return lhs.first < rhs.first;
});