map的用法

#include<iostream>#include<map>using namespace std;struct comp{/* data */typedef std::pair<int,int> value_type;bool operator()(const value_type &ls,const value_type &rs){return (ls.first<rs.first)||(ls.first==rs.first&& ls.second<rs.second);}};int main(){std::map<std::pair<int,int>, int,comp> map1;map1.insert(make_pair(make_pair(12,56),56));//error: no matching function for call to `std::map<std::pair<int, int>, int, std::less<std::pair<int, int> >,// std::allocator<std::pair<const std::pair<int, int>, int> > >::insert(std::pair<int, int>, int)'    map1.insert(std::make_pair(std::make_pair(121,331), 331));   std::map<std::pair<int, int>, int, comp>::iterator it = map1.find(std::make_pair(121,331));         if (it == map1.end())                 printf("NULL\n");           else                printf("%d %d %d \n", it->first.first, it->first.second, it->second);  system("pause");return 0;}