【STL】-pair的用法

初始化：

　　std::pair<int, float> p; //initialize p.first and p.second with zero

　　std::pair<int, const char*> p(42, "hello");

　　make_pair(42, "hello"); // no need for the var name, it's returned by make_pair

　　make_pair<int, float>(42, "hello");