Properly dereferencing an array of strings

Question

I'm working on a spell checking program for a class and am running into trouble trying to make the hash array accessible to other functions by using pointers.

Below is just a small part of the code since the program is too large to paste. Basic idea of this part of the code is:

-Create array and pointer to array. -Hash each word and use the value as index in array. -Use pointer to store the hashed value. -Access the array using the pointer for the array and hashed value.

As noted below, directly accessing the word stored in the array works, but I get a seg fault when trying to use the pointers to access the word stored in the array.

==1845== Invalid read of size 8
==1845==    at 0x401367: load (dictionary.c:133)
==1845==    by 0x40095D: main (speller.c:45)
==1845==  Address 0xfffc3fab8 is not stack'd, malloc'd or (recently) free'd


char** hash_array = calloc(HASH_TABLE_SIZE, sizeof(*hash_array));
char*** array_pointer;

// storing the address of the hash array in pointer
array_pointer = &hash_array;

uint32_t* hash_pointer;
hash_pointer = NULL;

uint32_t hash = hashlittle(word_buffer, word_length, 1578459744);
hash_pointer = &hash;

// this prints out the word successfully
printf("word in h-array: %s\n", hash_array[hash]);

// this seg faults
printf("word in h-array: %s\n", *array_pointer[*hash_pointer]);

Answer 1

The issue you're seeing is because of the operator precedence of the dereference operator * .

The following are all equivalent:

*array_pointer[*hash_pointer]

*array_pointer[hash]

*(array_pointer[hash])

*((&hash_array)[hash])

*(*(&hash_array + hash))

The problem is here: *(&hash_array + hash) . You're attempting to dereference a pointer to some memory location offset from the location of where the pointer hash_array is stored, rather than where it points, which is causing undefined behavior.