HASH(3)

NAME
hash_create, hash_destroy, hash_install, hash_lookup, hash_uninstall, hash_iter - generic hash tables

SYNOPSIS
#include <publib.h>

Hashtab *hash_create(unsigned long (*fun)(void *),
         int (*cmp)(const void *, const void *));
void hash_destroy(Hashtab *ht);
void *hash_install(Hashtab *ht, void *data, size_t size);
void *hash_lookup(Hashtab *ht, void *data);
int hash_uninstall(Hashtab *ht, void *data);
int hash_iter(Hashtab *ht, int (*doit)(void *, void *), void *param);

DESCRIPTION
These functions implement generic hash tables. The table is created by hash_create and destroyed by hash_destroy. The fun argument is a pointer to the hashing function, which must convert a datum to an unsigned long, which is then converted to an index into the hashing table. cmp is a qsort(3)-like comparison functions, used to compare to (wannabe) hash table elements.

hash_install installs a new datum into the table. A pointer to the data and the size of the data are given as the arguments. If the size is 0, only the pointer value is copied to the table. Otherwise a copy of the data is made into dynamically allocated memory.

hash_lookup attempts to find a datum in the hash table. A pointer to another datum is given as the argument. The comparison function should compare equal (return 0) the desired datum and this datum (but the argument needn't be a fully initialized datum, although that is up to the writer of the comparison function). There cannot be two elements in the hash table that are equal (the comparison function returns 0 for them). It is up to the user to handle collisions.

hash_uninstall removes an element from a table. The argument is a pointer to a datum that identifies the element.

hash_iter goes through every element in the hash table and calls the doit function for each. The first argument it provides to doit is the element in question, the second is whatever was given to hash_iter as param. If doit returns -1 or 0 for any element in the hash table, hash_iter immediately returns without going through the remaining elements in the hash table. Any other return value from doit is ignored.

RETURNS
hash_create returns a pointer to the new hash table, or NULL if it fails.

hash_install returns a pointer to an element in the table (either the installed one, or one that was already installed, if one tries to install the same datum twice).

hash_uninstall returns 0 if it found the element in the array, or -1 if it didn't.

hash_lookup return a pointer to the element it finds, or NULL if it doesn't find anything beautiful.

hash_iter returns -1, 0, or 1. If hash_iter receives a return value of -1 or 0 for some element from doit, hash_iter immediately returns -1 or 0, respectively. In all other cases hash_iter returns 1.

SEE ALSO
publib(3), qsort(3), bsearch(3)

AUTHOR
Lars Wirzenius (lars.wirzenius@helsinki.fi)