关于map的erase方法的使用

   void erase( iterator pos ); 

   void erase( iterator start, iterator end ); 

   size_type erase( const KEY_TYPE &key );  

  

    map<int,int> mp;

    mp[1] = 2;
    mp[2] = 3;
    mp[3] = 4;
    map<int,int>::size_type ret = mp.erase(0);
    printf("retis %u\n",ret);//打印0
    ret = mp.erase(3);
    printf("ret is %u\n",ret);//打印1