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Associative arrays/Creation/C: Difference between revisions
Add simple simple way to create hash tables in C
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* Back to [[Associative arrays/Creation]].
* Back to [[Associative arrays/Iteration]].
==From Scratch==
A hash table can be implemented with the following. Because of this example's simplicity, it comes with some restrictions on use and capabilities: It can't be resized automatically, if you try to insert values than its capacity it will freeze, the hashing function is very simple, etc. All are fixable with additional logic or using a library:
<lang c>typedef struct {
int size;
void **keys;
void **values;
} Hash;
Hash *hash_new (int size) {
Hash *hash = calloc(1, sizeof (Hash));
hash->size = size;
hash->keys = calloc(size, sizeof (void *));
hash->values = calloc(size, sizeof (void *));
return hash;
}
void hash_free (Hash *hash) {
free(hash->keys);
free(hash->values);
free(hash);
}
int hash_index (Hash *hash, void *key) {
int index = (int) key % hash->size;
while (hash->keys[index] && hash->keys[index] != key)
index = (index + 1) % hash->size;
return index;
}
void hash_insert (Hash *hash, void *key, void *value) {
int index = hash_index(hash, key);
hash->keys[index] = key;
hash->values[index] = value;
}
void *hash_lookup (Hash *hash, void *key) {
int index = hash_index(hash, key);
return hash->values[index];
}
int main () {
Hash *hash = hash_new(15);
hash_insert(hash, "hello", "world");
hash_insert(hash, "a", "b");
printf("hello => %s\n", hash_lookup(hash, "hello"));
printf("herp => %s\n", hash_lookup(hash, "herp"));
printf("a => %s\n", hash_lookup(hash, "a"));
return 0;
}</lang>
==Libraries==
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