GHashTable

typedef struct _GHashTable GHashTable;

The GHashTable struct is an opaque data structure to represent a Hash Table. It should only be accessed via the following functions.

g_hash_table_new ()

GHashTable *        g_hash_table_new                    (GHashFunc hash_func,
                                                         GEqualFunc key_equal_func);

Creates a new GHashTable with a reference count of 1.

g_hash_table_new_full ()

GHashTable *        g_hash_table_new_full               (GHashFunc hash_func,
                                                         GEqualFunc key_equal_func,
                                                         GDestroyNotify key_destroy_func,
                                                         GDestroyNotify value_destroy_func);

Creates a new GHashTable like g_hash_table_new() with a reference count of 1 and allows to specify functions to free the memory allocated for the key and value that get called when removing the entry from the GHashTable.

GHashFunc ()

guint               (*GHashFunc)                        (gconstpointer key);

Specifies the type of the hash function which is passed to g_hash_table_new() when a GHashTable is created.

The function is passed a key and should return a guint hash value. The functions g_direct_hash(), g_int_hash() and g_str_hash() provide hash functions which can be used when the key is a gpointer, gint, and gchar* respectively.

The hash values should be evenly distributed over a fairly large range? The modulus is taken with the hash table size (a prime number) to find the 'bucket' to place each key into. The function should also be very fast, since it is called for each key lookup.

GEqualFunc ()

gboolean            (*GEqualFunc)                       (gconstpointer a,
                                                         gconstpointer b);

Specifies the type of a function used to test two values for equality. The function should return TRUE if both values are equal and FALSE otherwise.

g_hash_table_insert ()

void                g_hash_table_insert                 (GHashTable *hash_table,
                                                         gpointer key,
                                                         gpointer value);

Inserts a new key and value into a GHashTable.

If the key already exists in the GHashTable its current value is replaced with the new value. If you supplied a value_destroy_func when creating the GHashTable, the old value is freed using that function. If you supplied a key_destroy_func when creating the GHashTable, the passed key is freed using that function.

g_hash_table_replace ()

void                g_hash_table_replace                (GHashTable *hash_table,
                                                         gpointer key,
                                                         gpointer value);

Inserts a new key and value into a GHashTable similar to g_hash_table_insert(). The difference is that if the key already exists in the GHashTable, it gets replaced by the new key. If you supplied a value_destroy_func when creating the GHashTable, the old value is freed using that function. If you supplied a key_destroy_func when creating the GHashTable, the old key is freed using that function.

g_hash_table_size ()

guint               g_hash_table_size                   (GHashTable *hash_table);

Returns the number of elements contained in the GHashTable.

g_hash_table_lookup ()

gpointer            g_hash_table_lookup                 (GHashTable *hash_table,
                                                         gconstpointer key);

Looks up a key in a GHashTable. Note that this function cannot distinguish between a key that is not present and one which is present and has the value NULL. If you need this distinction, use g_hash_table_lookup_extended().

g_hash_table_lookup_extended ()

gboolean            g_hash_table_lookup_extended        (GHashTable *hash_table,
                                                         gconstpointer lookup_key,
                                                         gpointer *orig_key,
                                                         gpointer *value);

Looks up a key in the GHashTable, returning the original key and the associated value and a gboolean which is TRUE if the key was found. This is useful if you need to free the memory allocated for the original key, for example before calling g_hash_table_remove().

You can actually pass NULL for lookup_key to test whether the NULL key exists, provided the hash and equal functions of hash_table are NULL-safe.

g_hash_table_foreach ()

void                g_hash_table_foreach                (GHashTable *hash_table,
                                                         GHFunc func,
                                                         gpointer user_data);

Calls the given function for each of the key/value pairs in the GHashTable. The function is passed the key and value of each pair, and the given user_data parameter. The hash table may not be modified while iterating over it (you can't add/remove items). To remove all items matching a predicate, use g_hash_table_foreach_remove().

See g_hash_table_find() for performance caveats for linear order searches in contrast to g_hash_table_lookup().

g_hash_table_find ()

gpointer            g_hash_table_find                   (GHashTable *hash_table,
                                                         GHRFunc predicate,
                                                         gpointer user_data);

Calls the given function for key/value pairs in the GHashTable until predicate returns TRUE. The function is passed the key and value of each pair, and the given user_data parameter. The hash table may not be modified while iterating over it (you can't add/remove items).

Note, that hash tables are really only optimized for forward lookups, i.e. g_hash_table_lookup(). So code that frequently issues g_hash_table_find() or g_hash_table_foreach() (e.g. in the order of once per every entry in a hash table) should probably be reworked to use additional or different data structures for reverse lookups (keep in mind that an O(n) find/foreach operation issued for all n values in a hash table ends up needing O(n*n) operations).

Since 2.4

GHFunc ()

void                (*GHFunc)                           (gpointer key,
                                                         gpointer value,
                                                         gpointer user_data);

Specifies the type of the function passed to g_hash_table_foreach(). It is called with each key/value pair, together with the user_data parameter which is passed to g_hash_table_foreach().

g_hash_table_remove ()

gboolean            g_hash_table_remove                 (GHashTable *hash_table,
                                                         gconstpointer key);

Removes a key and its associated value from a GHashTable.

If the GHashTable was created using g_hash_table_new_full(), the key and value are freed using the supplied destroy functions, otherwise you have to make sure that any dynamically allocated values are freed yourself.

g_hash_table_steal ()

gboolean            g_hash_table_steal                  (GHashTable *hash_table,
                                                         gconstpointer key);

Removes a key and its associated value from a GHashTable without calling the key and value destroy functions.

g_hash_table_foreach_remove ()

guint               g_hash_table_foreach_remove         (GHashTable *hash_table,
                                                         GHRFunc func,
                                                         gpointer user_data);

Calls the given function for each key/value pair in the GHashTable. If the function returns TRUE, then the key/value pair is removed from the GHashTable. If you supplied key or value destroy functions when creating the GHashTable, they are used to free the memory allocated for the removed keys and values.

See GHashTableIter for an alternative way to loop over the key/value pairs in the hash table.

g_hash_table_foreach_steal ()

guint               g_hash_table_foreach_steal          (GHashTable *hash_table,
                                                         GHRFunc func,
                                                         gpointer user_data);

Calls the given function for each key/value pair in the GHashTable. If the function returns TRUE, then the key/value pair is removed from the GHashTable, but no key or value destroy functions are called.

See GHashTableIter for an alternative way to loop over the key/value pairs in the hash table.

g_hash_table_remove_all ()

void                g_hash_table_remove_all             (GHashTable *hash_table);

Removes all keys and their associated values from a GHashTable.

If the GHashTable was created using g_hash_table_new_full(), the keys and values are freed using the supplied destroy functions, otherwise you have to make sure that any dynamically allocated values are freed yourself.

Since 2.12

g_hash_table_steal_all ()

void                g_hash_table_steal_all              (GHashTable *hash_table);

Removes all keys and their associated values from a GHashTable without calling the key and value destroy functions.

Since 2.12

g_hash_table_get_keys ()

GList *             g_hash_table_get_keys               (GHashTable *hash_table);

Retrieves every key inside hash_table. The returned data is valid until hash_table is modified.

Since 2.14

g_hash_table_get_values ()

GList *             g_hash_table_get_values             (GHashTable *hash_table);

Retrieves every value inside hash_table. The returned data is valid until hash_table is modified.

Since 2.14

GHRFunc ()

gboolean            (*GHRFunc)                          (gpointer key,
                                                         gpointer value,
                                                         gpointer user_data);

Specifies the type of the function passed to g_hash_table_foreach_remove(). It is called with each key/value pair, together with the user_data parameter passed to g_hash_table_foreach_remove(). It should return TRUE if the key/value pair should be removed from the GHashTable.

g_hash_table_freeze()

#define             g_hash_table_freeze(hash_table)

This function is deprecated and will be removed in the next major release of GLib. It does nothing.

g_hash_table_thaw()

#define             g_hash_table_thaw(hash_table)

This function is deprecated and will be removed in the next major release of GLib. It does nothing.

g_hash_table_destroy ()

void                g_hash_table_destroy                (GHashTable *hash_table);

Destroys all keys and values in the GHashTable and decrements its reference count by 1. If keys and/or values are dynamically allocated, you should either free them first or create the GHashTable with destroy notifiers using g_hash_table_new_full(). In the latter case the destroy functions you supplied will be called on all keys and values during the destruction phase.

g_hash_table_ref ()

GHashTable *        g_hash_table_ref                    (GHashTable *hash_table);

Atomically increments the reference count of hash_table by one. This function is MT-safe and may be called from any thread.

Since 2.10

g_hash_table_unref ()

void                g_hash_table_unref                  (GHashTable *hash_table);

Atomically decrements the reference count of hash_table by one. If the reference count drops to 0, all keys and values will be destroyed, and all memory allocated by the hash table is released. This function is MT-safe and may be called from any thread.

Since 2.10

struct GHashTableIter

struct GHashTableIter {
};

A GHashTableIter structure represents an iterator that can be used to iterate over the elements of a GHashTable. GHashTableIter structures are typically allocated on the stack and then initialized with g_hash_table_iter_init().

g_hash_table_iter_init ()

void                g_hash_table_iter_init              (GHashTableIter *iter,
                                                         GHashTable *hash_table);

Initializes a key/value pair iterator and associates it with hash_table. Modifying the hash table after calling this function invalidates the returned iterator.

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GHashTableIter iter;
gpointer key, value;

g_hash_table_iter_init (&iter, hash_table);
while (g_hash_table_iter_next (&iter, &key, &value)) 
  {
    /* do something with key and value */
  }

Since 2.16

g_hash_table_iter_next ()

gboolean            g_hash_table_iter_next              (GHashTableIter *iter,
                                                         gpointer *key,
                                                         gpointer *value);

Advances iter and retrieves the key and/or value that are now pointed to as a result of this advancement. If FALSE is returned, key and value are not set, and the iterator becomes invalid.

Since 2.16

g_hash_table_iter_get_hash_table ()

GHashTable *        g_hash_table_iter_get_hash_table    (GHashTableIter *iter);

Returns the GHashTable associated with iter.

Since 2.16

g_hash_table_iter_remove ()

void                g_hash_table_iter_remove            (GHashTableIter *iter);

Removes the key/value pair currently pointed to by the iterator from its associated GHashTable. Can only be called after g_hash_table_iter_next() returned TRUE, and cannot be called more than once for the same key/value pair.

If the GHashTable was created using g_hash_table_new_full(), the key and value are freed using the supplied destroy functions, otherwise you have to make sure that any dynamically allocated values are freed yourself.

Since 2.16

g_hash_table_iter_steal ()

void                g_hash_table_iter_steal             (GHashTableIter *iter);

Removes the key/value pair currently pointed to by the iterator from its associated GHashTable, without calling the key and value destroy functions. Can only be called after g_hash_table_iter_next() returned TRUE, and cannot be called more than once for the same key/value pair.

Since 2.16

g_direct_equal ()

gboolean            g_direct_equal                      (gconstpointer v1,
                                                         gconstpointer v2);

Compares two gpointer arguments and returns TRUE if they are equal. It can be passed to g_hash_table_new() as the key_equal_func parameter, when using pointers as keys in a GHashTable.

g_direct_hash ()

guint               g_direct_hash                       (gconstpointer v);

Converts a gpointer to a hash value. It can be passed to g_hash_table_new() as the hash_func parameter, when using pointers as keys in a GHashTable.

g_int_equal ()

gboolean            g_int_equal                         (gconstpointer v1,
                                                         gconstpointer v2);

Compares the two gint values being pointed to and returns TRUE if they are equal. It can be passed to g_hash_table_new() as the key_equal_func parameter, when using pointers to integers as keys in a GHashTable.

g_int_hash ()

guint               g_int_hash                          (gconstpointer v);

Converts a pointer to a gint to a hash value. It can be passed to g_hash_table_new() as the hash_func parameter, when using pointers to integers values as keys in a GHashTable.

g_int64_equal ()

gboolean            g_int64_equal                       (gconstpointer v1,
                                                         gconstpointer v2);

Compares the two gint64 values being pointed to and returns TRUE if they are equal. It can be passed to g_hash_table_new() as the key_equal_func parameter, when using pointers to 64-bit integers as keys in a GHashTable.

Since 2.22

g_int64_hash ()

guint               g_int64_hash                        (gconstpointer v);

Converts a pointer to a gint64 to a hash value. It can be passed to g_hash_table_new() as the hash_func parameter, when using pointers to 64-bit integers values as keys in a GHashTable.

Since 2.22

g_double_equal ()

gboolean            g_double_equal                      (gconstpointer v1,
                                                         gconstpointer v2);

Compares the two gdouble values being pointed to and returns TRUE if they are equal. It can be passed to g_hash_table_new() as the key_equal_func parameter, when using pointers to doubles as keys in a GHashTable.

Since 2.22

g_double_hash ()

guint               g_double_hash                       (gconstpointer v);

Converts a pointer to a gdouble to a hash value. It can be passed to g_hash_table_new() as the hash_func parameter, when using pointers to doubles as keys in a GHashTable.

Since 2.22

g_str_equal ()

gboolean            g_str_equal                         (gconstpointer v1,
                                                         gconstpointer v2);

Compares two strings for byte-by-byte equality and returns TRUE if they are equal. It can be passed to g_hash_table_new() as the key_equal_func parameter, when using strings as keys in a GHashTable.

Note that this function is primarily meant as a hash table comparison function. For a general-purpose, NULL-safe string comparison function, see g_strcmp0().

g_str_hash ()

guint               g_str_hash                          (gconstpointer v);

Converts a string to a hash value.

This function implements the widely used "djb" hash apparently posted by Daniel Bernstein to comp.lang.c some time ago. The 32 bit unsigned hash value starts at 5381 and for each byte 'c' in the string, is updated: hash = hash * 33 + c. This function uses the signed value of each byte.

It can be passed to g_hash_table_new() as the hash_func parameter, when using strings as keys in a GHashTable.