hash_map之自己构造hash函数和查找函数

#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;
}