Question

I’m having trouble to implement a simple list in C, the problem is the connection of the items via pointers.
The following piece of code is a snippet from a hashtable, which is supposed to store items with the same index in a list to avoid collisions.

typedef struct dictEntry {
    void *key;
    void *value;
    struct dictEntry *next;
} dictEntry;

typedef struct dict {
    dictEntry **table;
    unsigned long size;
    unsigned long used;
} dict;

void dictAdd(dict *d, void *key, void *value) {
    int index = hash(key) & d->size;
    dictEntry *entry;

    entry = malloc(sizeof(entry));

    entry->key   = key;
    entry->value = value;
    entry->next  = 0;

    if (d->table[index]) {
        /* this is does not work */
        dictEntry *next;
        next = d->table[index];

        while (next) {
            next = next->next;
        }

        next = entry;
    } else {
        d->table[index] = entry;
        d->used++;
    }
}

My thinking was to iterate through every element of the list (next->next) and assign the pointer of entry to the last element (next = entry;).
After a few days of rewriting and moving parts of the code around, I still can’t seem to find a solution.

Answer 1

You should try to implement the linked list first.

Here’s how I would implement the addition to the end (I’ve modified your code where you just overwrite the temporary “next” variable without modifying the list itself):

if (d->table[index]) {
    /* this should work*/
    dictEntry *next;
    dictEntry *prev = NULL;
    next = d->table[index];

    while (next) {
        prev = next;
        next = next->next;
    }

    // yes, add new entry as the "next" pointer to the "last" item
    prev->next = entry;
} else {

….