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Our hash table implementation

This is a generic hash table implementation used in several coral applications, but is not an essential part of libcoral.

To create a hash table, use init_hash_table(), which sets up the hash table and all of the necessary functions for using it. So before doing this, you must create three functions:

Comparison function

int compare_function(const void *, const void *);

This function is used to check the equality of two entries.
Returns 0 if equal, non-zero otherwise.

Example:

int compare_long(const void * entry1, const void * entry2)
{
    static long * typed_entry1 = (long *)entry1;
    static long * typed_entry2 = (long *)entry2;
    return *typed_entry1 == *typed_entry2;
}

Key Generation function

unsigned long key_function(const void *);

This function takes the pointer to an entry and creates a key from it. eg, a struct might have one of its members as a key, a long would just be its own key.

Example:

unsigned long make_key_long(const void * entry)
{
    static long * typed_entry = (long *)entry;
    return *typed_entry;
}

Deletion function

void delete_function(void *);

This function is called when a hash entry is to be deleted.

Example:

void delete_long(void * entry)
{
    static long * typed_entry = (long *)entry;
    free(typed_entry);
}

Once these functions are defined, you can create a hash table thusly:

....
hash_tab * long_hash;
long_hash = init_hash_table("My table of longs", compare_long, make_key_long,
			    delete_long, 101);
....

The rest of the functions are fairly self-explanatory and can be demonstrated with code examples:

long * new_entry;
long check_entry;
long * found_entry;

new_entry = (long *)malloc(sizeof(long));
*new_entry = 3.14159;
check_entry = 2.7;
add_hash_entry(long_hash, new_entry);
found_entry = (long *)find_hash_entry(long_hash, &check_entry);
if (found_entry == NULL) {
    printf("Hey, I couldn't find it!\n");
} else {
    *found_entry = 22/7;
}

init_hash_walk(long_hash);
while (found_entry = next_hash_walk(long_hash)) {
    printf("Found this entry: %d\n", *found_entry);
}
dump_hashtab_stats(long_hash);

clear_hash_entry(long_hash, found_entry);
clear_hash_table(long_hash);
free_hash_table(long_hash);

Notes:

add_hash_entry() does NOT copy the entry, so make sure not to pass in pointers to local variables.
find_hash_entry() returns the pointer to the actual data in the hashtable, so any modifications are made in the hashtable.
dump_hashtab_stats() dumps to stdout.

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Problems? Write us:

coral-bugs@caida.org