Hash table implementation bad access error - c

Question

I was trying to make a hash table for my project but I keep getting bad access error. There is no mistake in syntax as compiler tells me. I think I have made a mistake in memory allocation but I can't see it. Any help is appreciated.
I get a bad access error in this loop:
hash_itself_p hash_table = (hash_itself_p)malloc(sizeof(hash_itself_t));
for (i = 0; i < 50; i++)
{
hash_table->data_id[i]->id = -1; // EXC_BAD_ACCESS here
}
And here is the all of the code:
#include <stdio.h>
#include <stdlib.h>
#define size 50
typedef struct hash_value
{
int id;
int data;
int key;
} hash_values_t[1], *hash_values;
typedef struct hash_itself
{
hash_values data_id[size];
} hash_itself_t[1], *hash_itself_p;
int hash_key(int n)
{
return ( n*n + 2*n ) % size;
}
int hash_id(int n)
{
return n % size;
}
void insert(hash_itself_p hash_table, int person)
{
int id;
int key;
key = hash_key(person);
id = hash_id(key);
if (hash_table->data_id[id]->id == -1)
{
hash_table->data_id[id]->id = id;
hash_table->data_id[id]->data = person;
}
else
{
int block = id;
while (hash_table->data_id[block%50]->id != -1)
{
block++;
if (block%50 == id) return;
}
hash_table->data_id[block]->id = id;
hash_table->data_id[block]->data = person;
}
}
void display(hash_itself_p hash_table)
{
int i;
for (i = 0; i < size; i++)
{
printf("id = %d, data = %d, key = %d \n", hash_table->data_id[i]->id, hash_table->data_id[i]->data, hash_table->data_id[i]->key);
}
}
int main()
{
int i;
hash_itself_p hash_table = (hash_itself_p)malloc(sizeof(hash_itself_t));
for (i = 0; i < 50; i++)
{
hash_table->data_id[i]->id = -1;
}
insert(hash_table, 30);
display(hash_table);
}

Answer 1

You've declared the data_id array in hash_itself as an array of pointers to hash_value structs. Since those pointers are not initialized, it accesses invalid memory.
I think you wanted to create an array of the structs directly, in which case you want:
typedef struct hash_itself
{
hash_values_t data_id[size];
}