zhash man page

zhash — simple generic hash container

Synopsis

//  This is a stable class, and may not change except for emergencies. It
//  is provided in stable builds.
// Callback function for zhash_freefn method
typedef void (zhash_free_fn) (
    void *data);

//  Create a new, empty hash container
CZMQ_EXPORT zhash_t *
    zhash_new (void);

//  Unpack binary frame into a new hash table. Packed data must follow format
//  defined by zhash_pack. Hash table is set to autofree. An empty frame
//  unpacks to an empty hash table.
CZMQ_EXPORT zhash_t *
    zhash_unpack (zframe_t *frame);

//  Destroy a hash container and all items in it
CZMQ_EXPORT void
    zhash_destroy (zhash_t **self_p);

//  Insert item into hash table with specified key and item.
//  If key is already present returns -1 and leaves existing item unchanged
//  Returns 0 on success.
CZMQ_EXPORT int
    zhash_insert (zhash_t *self, const char *key, void *item);

//  Update item into hash table with specified key and item.
//  If key is already present, destroys old item and inserts new one.
//  Use free_fn method to ensure deallocator is properly called on item.
CZMQ_EXPORT void
    zhash_update (zhash_t *self, const char *key, void *item);

//  Remove an item specified by key from the hash table. If there was no such
//  item, this function does nothing.
CZMQ_EXPORT void
    zhash_delete (zhash_t *self, const char *key);

//  Return the item at the specified key, or null
CZMQ_EXPORT void *
    zhash_lookup (zhash_t *self, const char *key);

//  Reindexes an item from an old key to a new key. If there was no such
//  item, does nothing. Returns 0 if successful, else -1.
CZMQ_EXPORT int
    zhash_rename (zhash_t *self, const char *old_key, const char *new_key);

//  Set a free function for the specified hash table item. When the item is
//  destroyed, the free function, if any, is called on that item.
//  Use this when hash items are dynamically allocated, to ensure that
//  you don't have memory leaks. You can pass 'free' or NULL as a free_fn.
//  Returns the item, or NULL if there is no such item.
CZMQ_EXPORT void *
    zhash_freefn (zhash_t *self, const char *key, zhash_free_fn free_fn);

//  Return the number of keys/items in the hash table
CZMQ_EXPORT size_t
    zhash_size (zhash_t *self);

//  Make copy of hash table; if supplied table is null, returns null.
//  Does not copy items themselves. Rebuilds new table so may be slow on
//  very large tables. NOTE: only works with item values that are strings
//  since there's no other way to know how to duplicate the item value.
//  Caller owns return value and must destroy it when done.
CZMQ_EXPORT zhash_t *
    zhash_dup (zhash_t *self);

//  Return keys for items in table
//  Caller owns return value and must destroy it when done.
CZMQ_EXPORT zlist_t *
    zhash_keys (zhash_t *self);

//  Simple iterator; returns first item in hash table, in no given order,
//  or NULL if the table is empty. This method is simpler to use than the
//  foreach() method, which is deprecated. To access the key for this item
//  use zhash_cursor(). NOTE: do NOT modify the table while iterating.
CZMQ_EXPORT void *
    zhash_first (zhash_t *self);

//  Simple iterator; returns next item in hash table, in no given order,
//  or NULL if the last item was already returned. Use this together with
//  zhash_first() to process all items in a hash table. If you need the
//  items in sorted order, use zhash_keys() and then zlist_sort(). To
//  access the key for this item use zhash_cursor(). NOTE: do NOT modify
//  the table while iterating.
CZMQ_EXPORT void *
    zhash_next (zhash_t *self);

//  After a successful first/next method, returns the key for the item that
//  was returned. This is a constant string that you may not modify or
//  deallocate, and which lasts as long as the item in the hash. After an
//  unsuccessful first/next, returns NULL.
CZMQ_EXPORT const char *
    zhash_cursor (zhash_t *self);

//  Add a comment to hash table before saving to disk. You can add as many
//  comment lines as you like. These comment lines are discarded when loading
//  the file. If you use a null format, all comments are deleted.
CZMQ_EXPORT void
    zhash_comment (zhash_t *self, const char *format, ...) CHECK_PRINTF (2);

//  Serialize hash table to a binary frame that can be sent in a message.
//  The packed format is compatible with the 'dictionary' type defined in
//  http://rfc.zeromq.org/spec:35/FILEMQ, and implemented by zproto:
//
//     ; A list of name/value pairs
//     dictionary      = dict-count *( dict-name dict-value )
//     dict-count      = number-4
//     dict-value      = longstr
//     dict-name       = string
//
//     ; Strings are always length + text contents
//     longstr         = number-4 *VCHAR
//     string          = number-1 *VCHAR
//
//     ; Numbers are unsigned integers in network byte order
//     number-1        = 1OCTET
//     number-4        = 4OCTET
//
//  Comments are not included in the packed data. Item values MUST be
//  strings.
//  Caller owns return value and must destroy it when done.
CZMQ_EXPORT zframe_t *
    zhash_pack (zhash_t *self);

//  Save hash table to a text file in name=value format. Hash values must be
//  printable strings; keys may not contain '=' character. Returns 0 if OK,
//  else -1 if a file error occurred.
CZMQ_EXPORT int
    zhash_save (zhash_t *self, const char *filename);

//  Load hash table from a text file in name=value format; hash table must
//  already exist. Hash values must printable strings; keys may not contain
//  '=' character. Returns 0 if OK, else -1 if a file was not readable.
CZMQ_EXPORT int
    zhash_load (zhash_t *self, const char *filename);

//  When a hash table was loaded from a file by zhash_load, this method will
//  reload the file if it has been modified since, and is "stable", i.e. not
//  still changing. Returns 0 if OK, -1 if there was an error reloading the
//  file.
CZMQ_EXPORT int
    zhash_refresh (zhash_t *self);

//  Set hash for automatic value destruction
CZMQ_EXPORT void
    zhash_autofree (zhash_t *self);

//  Self test of this class.
CZMQ_EXPORT void
    zhash_test (bool verbose);

Description

zhash is an expandable hash table container. This is a simple container. For heavy-duty applications we recommend using zhashx.

Note that it’s relatively slow (50K insertions/deletes per second), so don’t do inserts/updates on the critical path for message I/O. It can do 2.5M lookups per second for 16-char keys. Timed on a 1.6GHz CPU.

Example

From zhash_test method.

zhash_t *hash = zhash_new ();
assert (hash);
assert (zhash_size (hash) == 0);
assert (zhash_first (hash) == NULL);
assert (zhash_cursor (hash) == NULL);

//  Insert some items
int rc;
rc = zhash_insert (hash, "DEADBEEF", "dead beef");
char *item = (char *) zhash_first (hash);
assert (streq (zhash_cursor (hash), "DEADBEEF"));
assert (streq (item, "dead beef"));
assert (rc == 0);
rc = zhash_insert (hash, "ABADCAFE", "a bad cafe");
assert (rc == 0);
rc = zhash_insert (hash, "C0DEDBAD", "coded bad");
assert (rc == 0);
rc = zhash_insert (hash, "DEADF00D", "dead food");
assert (rc == 0);
assert (zhash_size (hash) == 4);

//  Look for existing items
item = (char *) zhash_lookup (hash, "DEADBEEF");
assert (streq (item, "dead beef"));
item = (char *) zhash_lookup (hash, "ABADCAFE");
assert (streq (item, "a bad cafe"));
item = (char *) zhash_lookup (hash, "C0DEDBAD");
assert (streq (item, "coded bad"));
item = (char *) zhash_lookup (hash, "DEADF00D");
assert (streq (item, "dead food"));

//  Look for non-existent items
item = (char *) zhash_lookup (hash, "foo");
assert (item == NULL);

//  Try to insert duplicate items
rc = zhash_insert (hash, "DEADBEEF", "foo");
assert (rc == -1);
item = (char *) zhash_lookup (hash, "DEADBEEF");
assert (streq (item, "dead beef"));

//  Some rename tests

//  Valid rename, key is now LIVEBEEF
rc = zhash_rename (hash, "DEADBEEF", "LIVEBEEF");
assert (rc == 0);
item = (char *) zhash_lookup (hash, "LIVEBEEF");
assert (streq (item, "dead beef"));

//  Trying to rename an unknown item to a non-existent key
rc = zhash_rename (hash, "WHATBEEF", "NONESUCH");
assert (rc == -1);

//  Trying to rename an unknown item to an existing key
rc = zhash_rename (hash, "WHATBEEF", "LIVEBEEF");
assert (rc == -1);
item = (char *) zhash_lookup (hash, "LIVEBEEF");
assert (streq (item, "dead beef"));

//  Trying to rename an existing item to another existing item
rc = zhash_rename (hash, "LIVEBEEF", "ABADCAFE");
assert (rc == -1);
item = (char *) zhash_lookup (hash, "LIVEBEEF");
assert (streq (item, "dead beef"));
item = (char *) zhash_lookup (hash, "ABADCAFE");
assert (streq (item, "a bad cafe"));

//  Test keys method
zlist_t *keys = zhash_keys (hash);
assert (zlist_size (keys) == 4);
zlist_destroy (&keys);

//  Test dup method
zhash_t *copy = zhash_dup (hash);
assert (zhash_size (copy) == 4);
item = (char *) zhash_lookup (copy, "LIVEBEEF");
assert (item);
assert (streq (item, "dead beef"));
zhash_destroy (&copy);

//  Test pack/unpack methods
zframe_t *frame = zhash_pack (hash);
copy = zhash_unpack (frame);
zframe_destroy (&frame);
assert (zhash_size (copy) == 4);
item = (char *) zhash_lookup (copy, "LIVEBEEF");
assert (item);
assert (streq (item, "dead beef"));
zhash_destroy (&copy);

//  Test save and load
zhash_comment (hash, "This is a test file");
zhash_comment (hash, "Created by %s", "czmq_selftest");
zhash_save (hash, ".cache");
copy = zhash_new ();
assert (copy);
zhash_load (copy, ".cache");
item = (char *) zhash_lookup (copy, "LIVEBEEF");
assert (item);
assert (streq (item, "dead beef"));
zhash_destroy (&copy);
zsys_file_delete (".cache");

//  Delete a item
zhash_delete (hash, "LIVEBEEF");
item = (char *) zhash_lookup (hash, "LIVEBEEF");
assert (item == NULL);
assert (zhash_size (hash) == 3);

//  Check that the queue is robust against random usage
struct {
    char name [100];
    bool exists;
} testset [200];
memset (testset, 0, sizeof (testset));
int testmax = 200, testnbr, iteration;

srandom ((unsigned) time (NULL));
for (iteration = 0; iteration < 25000; iteration++) {
    testnbr = randof (testmax);
    if (testset [testnbr].exists) {
        item = (char *) zhash_lookup (hash, testset [testnbr].name);
        assert (item);
        zhash_delete (hash, testset [testnbr].name);
        testset [testnbr].exists = false;
    }
    else {
        sprintf (testset [testnbr].name, "%x-%x", rand (), rand ());
        if (zhash_insert (hash, testset [testnbr].name, "") == 0)
            testset [testnbr].exists = true;
    }
}
//  Test 10K lookups
for (iteration = 0; iteration < 10000; iteration++)
    item = (char *) zhash_lookup (hash, "DEADBEEFABADCAFE");

//  Destructor should be safe to call twice
zhash_destroy (&hash);
zhash_destroy (&hash);
assert (hash == NULL);

// Test autofree; automatically copies and frees string values
hash = zhash_new ();
assert (hash);
zhash_autofree (hash);
char value [255];
strcpy (value, "This is a string");
rc = zhash_insert (hash, "key1", value);
assert (rc == 0);
strcpy (value, "Inserting with the same key will fail");
rc = zhash_insert (hash, "key1", value);
assert (rc == -1);
strcpy (value, "Ring a ding ding");
rc = zhash_insert (hash, "key2", value);
assert (rc == 0);
assert (streq ((char *) zhash_lookup (hash, "key1"), "This is a string"));
assert (streq ((char *) zhash_lookup (hash, "key2"), "Ring a ding ding"));
zhash_destroy (&hash);

Authors

The czmq manual was written by the authors in the Authors file.

Resources

Main web site:

Report bugs to the email <zeromq-dev@lists.zeromq.org[1]>

Notes

1.

zeromq-dev@lists.zeromq.org

mailto:zeromq-dev@lists.zeromq.org

Referenced By

czmq(7).

11/11/2016 CZMQ 4.0.1 CZMQ Manual