Question

I’m trying to use a file pointer that I have declared in a structure of linked list, but I keep getting it as a NULL value.

I have the following structure:

struct _hash_table
{
    char found;
    struct _hash_chain *hash_chain;
}

struct _hash_chain
{
    uint64_t value;
    FILE *fout;
    struct _hash_chain *next;
}

and

struct _hash_table hash_table[TABLE_SIZE];

I keep getting hash_table[i]->hash_chain->fout = NULL and it’s pointer address is nil.

Do I need to dynamically allocate memory for the pointer?

Answer 1

struct _hash_table hash_table[TABLE_SIZE]; – This will not allocate memory for struct _hash_chain because hash_chain is pointer variable in _hash_table.

...
struct _hash_table hash_table[TABLE_SIZE];
for (i = 0; i < TABLE_SIZE; i++);
{
    hash_table[i].hash_chain = (struct _hash_chain *)malloc(sizeof(struct _hash_chain));
    memset(hash_table[i].hash_chain, 0, sizeof(struct _hash_chain));
}

//Then do file open for TABLE_SIZE times
//hash_table[0].hash_chain->fout = fopen("file.txt", "w");
...

Accssing h_table[i].hash_chain without dynamic memory allocation will leads to crash(an undefined behaviour). I hope you will take care of next pointer.