insertion to map- key is always exist

Question

I have an issue with inserting values to map.

#define SIZE 5
#define pair<unsigned char *, int> pair_t

struct myCmp
{
   int operator()(const unsigned char arr_1[SIZE], const unsigned char arr_2[SIZE])
   {
     printf("arr_1: %02x,%02x,%02x,%02x,%02x  arr_2: %02x,%02x,%02x,%02x,%02x", 
                  arr_1[0], arr_1[1],arr_1[2],arr_1[3],arr_1[4],
                  arr_2[0],arr_2[1],arr_2[2],arr_2[3],arr_2[4]);
   }
} 
void main()
{
  map<unsigned char *, int, myCmp> myMap;
  map<unsigned char *, int, myCmp>::iterator it;

  unsigned char arr[SIZE] = {'\0'};

  //---- first insertion ----//

  arr[0] 0xa;
  pait_t data_1(arr,1);
  pair< map<unsigned char *, int, myCmp>::iterator> ret_1 = myMap.insert(data_1);

  if(ret_1.second)
    printf("added one");

  else
    printf("already exist one");



 //---- second insertion ----//

  arr[1] 0xb;
  pait_t data_2(arr,2);
  pair< map<unsigned char *, int, myCmp>::iterator> ret_2 =  myMap.insert(data_2);

  if(ret_2.second)
    printf("added two");

  else
    printf("already exist two");
}

the first insertion is ok, myCmp is not activated yet and I get added one

the problem is with the second insertion, it seems that myCmp gets the same two arrays and always return 0 (equal)- it prints arr_1: ab arr_2: ab so the ret_2.second is false (key is already exist) and prints already exist two .

I tried to change the value of arr, but it doesn`t have any affect.

the strange part is when I tried to do the same but instead of char * I used string (changed the all the signatures of course..), the myCmp function got two different values.

I can`t use string as key..

I don't know why it behaves like this and myCmp gets two identical values.

I will be happy for guidance on that matter.

Answer 1

You're giving the arr address that is the same in both cases. Try using a std::string .