ZHASH(3) CZMQ Manual ZHASH(3) NAME zhash - Class for 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. Note that this assumes that // values are NULL-terminated strings. Do not use with different types. CZMQ_EXPORT void zhash_autofree (zhash_t *self); // Self test of this class. CZMQ_EXPORT void zhash_test (bool verbose); Please add '@interface' section in './../src/zhash.c'. 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 (©); // 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 (©); // 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 (©); 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); assert (testnbr != testmax); assert (testnbr < 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); #if defined (__WINDOWS__) zsys_shutdown(); #endif 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]> COPYRIGHT Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for 0MQ: http://czmq.zeromq.org. This Source Code Form is subject to the terms of the Mozilla Public Li- cense, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/. LICENSE included with the czmq distribution. NOTES 1. zeromq-dev@lists.zeromq.org mailto:zeromq-dev@lists.zeromq.org CZMQ 4.2.1 08/27/2026 ZHASH(3)
NAME | SYNOPSIS | DESCRIPTION | EXAMPLE | AUTHORS | RESOURCES | COPYRIGHT | NOTES
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