#include <hash_map> #include <string> #include <iostream> //#include <unordered_map> using namespace std; using namespace __gnu_cxx; //define the class class ClassA{ public: ClassA(int a):c_a(a){} int getvalue()const { return c_a;} void setvalue(int a){c_a;} private: int c_a; }; //1 define the hash function struct hash_A{ size_t operator()(const class ClassA & A)const{ // return hash<int>(classA.getvalue()); return A.getvalue(); } }; //2 define the equal function struct equal_A{ bool operator()(const class ClassA & a1, const class ClassA & a2)const{ return a1.getvalue() == a2.getvalue(); } }; int main() { hash_map<ClassA, string, hash_A, equal_A> hmap; ClassA a1(12); hmap[a1]="I am 12"; ClassA a2(198877); hmap[a2]="I am 198877"; cout<<hmap[a1]<<endl; cout<<hmap[a2]<<endl; return 0; }