GVariant Type Strings

A GVariant type string can be any of the following:

A basic type string describes a basic type (as per g_variant_type_is_basic()) and is always a single character in length. The valid basic type strings are "b", "y", "n", "q", "i", "u", "x", "t", "h", "d", "s", "o", "g" and "?".

The above definition is recursive to arbitrary depth. "aaaaai" and "(ui(nq((y)))s)" are both valid type strings, as is "a(aa(ui)(qna{ya(yd)}))".

The meaning of each of the characters is as follows:

Any type string of a container that contains an indefinite type is, itself, an indefinite type. For example, the type string "a*" (corresponding to G_VARIANT_TYPE_ARRAY) is an indefinite type that is a supertype of every array type. "(*s)" is a supertype of all tuples that contain exactly two items where the second item is a string.

"a{?*}" is an indefinite type that is a supertype of all arrays containing dictionary entries where the key is any basic type and the value is any type at all. This is, by definition, a dictionary, so this type string corresponds to G_VARIANT_TYPE_DICTIONARY. Note that, due to the restriction that the key of a dictionary entry must be a basic type, "{**}" is not a valid type string.

GVariantType

typedef struct _GVariantType GVariantType;

A type in the GVariant type system.

Two types may not be compared by value; use g_variant_type_equal() or g_variant_type_is_subtype(). May be copied using g_variant_type_copy() and freed using g_variant_type_free().

G_VARIANT_TYPE_BOOLEAN

#define G_VARIANT_TYPE_BOOLEAN              ((const GVariantType *) "b")

The type of a value that can be either TRUE or FALSE.

G_VARIANT_TYPE_BYTE

#define G_VARIANT_TYPE_BYTE                 ((const GVariantType *) "y")

The type of an integer value that can range from 0 to 255.

G_VARIANT_TYPE_INT16

#define G_VARIANT_TYPE_INT16                ((const GVariantType *) "n")

The type of an integer value that can range from -32768 to 32767.

G_VARIANT_TYPE_UINT16

#define G_VARIANT_TYPE_UINT16               ((const GVariantType *) "q")

The type of an integer value that can range from 0 to 65535. There were about this many people living in Toronto in the 1870s.

G_VARIANT_TYPE_INT32

#define G_VARIANT_TYPE_INT32                ((const GVariantType *) "i")

The type of an integer value that can range from -2147483648 to 2147483647.

G_VARIANT_TYPE_UINT32

#define G_VARIANT_TYPE_UINT32               ((const GVariantType *) "u")

The type of an integer value that can range from 0 to 4294967295. That's one number for everyone who was around in the late 1970s.

G_VARIANT_TYPE_INT64

#define G_VARIANT_TYPE_INT64                ((const GVariantType *) "x")

The type of an integer value that can range from -9223372036854775808 to 9223372036854775807.

G_VARIANT_TYPE_UINT64

#define G_VARIANT_TYPE_UINT64               ((const GVariantType *) "t")

The type of an integer value that can range from 0 to 18446744073709551616. That's a really big number, but a Rubik's cube can have a bit more than twice as many possible positions.

G_VARIANT_TYPE_HANDLE

#define G_VARIANT_TYPE_HANDLE               ((const GVariantType *) "h")

The type of a 32bit signed integer value, that by convention, is used as an index into an array of file descriptors that are sent alongside a DBus message.

If you are not interacting with DBus, then there is no reason to make use of this type.

G_VARIANT_TYPE_DOUBLE

#define G_VARIANT_TYPE_DOUBLE               ((const GVariantType *) "d")

The type of a double precision IEEE754 floating point number. These guys go up to about 1.80e308 (plus and minus) but miss out on some numbers in between. In any case, that's far greater than the estimated number of fundamental particles in the observable universe.

G_VARIANT_TYPE_STRING

#define G_VARIANT_TYPE_STRING               ((const GVariantType *) "s")

The type of a string. "" is a string. NULL is not a string.

G_VARIANT_TYPE_OBJECT_PATH

#define G_VARIANT_TYPE_OBJECT_PATH          ((const GVariantType *) "o")

The type of a DBus object reference. These are strings of a specific format used to identify objects at a given destination on the bus.

If you are not interacting with DBus, then there is no reason to make use of this type. If you are, then the DBus specification contains a precise description of valid object paths.

G_VARIANT_TYPE_SIGNATURE

#define G_VARIANT_TYPE_SIGNATURE            ((const GVariantType *) "g")

The type of a DBus type signature. These are strings of a specific format used as type signatures for DBus methods and messages.

If you are not interacting with DBus, then there is no reason to make use of this type. If you are, then the DBus specification contains a precise description of valid signature strings.

G_VARIANT_TYPE_VARIANT

#define G_VARIANT_TYPE_VARIANT              ((const GVariantType *) "v")

The type of a box that contains any other value (including another variant).

G_VARIANT_TYPE_ANY

#define G_VARIANT_TYPE_ANY                  ((const GVariantType *) "*")

An indefinite type that is a supertype of every type (including itself).

G_VARIANT_TYPE_BASIC

#define G_VARIANT_TYPE_BASIC                ((const GVariantType *) "?")

An indefinite type that is a supertype of every basic (ie: non-container) type.

G_VARIANT_TYPE_MAYBE

#define G_VARIANT_TYPE_MAYBE                ((const GVariantType *) "m*")

An indefinite type that is a supertype of every maybe type.

G_VARIANT_TYPE_ARRAY

#define G_VARIANT_TYPE_ARRAY                ((const GVariantType *) "a*")

An indefinite type that is a supertype of every array type.

G_VARIANT_TYPE_TUPLE

#define G_VARIANT_TYPE_TUPLE                ((const GVariantType *) "r")

An indefinite type that is a supertype of every tuple type, regardless of the number of items in the tuple.

G_VARIANT_TYPE_UNIT

#define G_VARIANT_TYPE_UNIT                 ((const GVariantType *) "()")

The empty tuple type. Has only one instance. Known also as "triv" or "void".

G_VARIANT_TYPE_DICT_ENTRY

#define G_VARIANT_TYPE_DICT_ENTRY           ((const GVariantType *) "{?*}")

An indefinite type that is a supertype of every dictionary entry type.

G_VARIANT_TYPE_DICTIONARY

#define G_VARIANT_TYPE_DICTIONARY           ((const GVariantType *) "a{?*}")

An indefinite type that is a supertype of every dictionary type -- that is, any array type that has an element type equal to any dictionary entry type.

G_VARIANT_TYPE()

#define             G_VARIANT_TYPE(type_string)

Converts a string to a const GVariantType. Depending on the current debugging level, this function may perform a runtime check to ensure that string is a valid GVariant type string.

It is always a programmer error to use this macro with an invalid type string.

Since 2.24

g_variant_type_free ()

void                g_variant_type_free                 (GVariantType *type);

Frees a GVariantType that was allocated with g_variant_type_copy(), g_variant_type_new() or one of the container type constructor functions.

In the case that type is NULL, this function does nothing.

Since 2.24

g_variant_type_copy ()

GVariantType *      g_variant_type_copy                 (const GVariantType *type);

Makes a copy of a GVariantType. It is appropriate to call g_variant_type_free() on the return value. type may not be NULL.

Since 2.24

g_variant_type_new ()

GVariantType *      g_variant_type_new                  (const gchar *type_string);

Creates a new GVariantType corresponding to the type string given by type_string. It is appropriate to call g_variant_type_free() on the return value.

It is a programmer error to call this function with an invalid type string. Use g_variant_type_string_is_valid() if you are unsure.

Since 2.24

g_variant_type_string_is_valid ()

gboolean            g_variant_type_string_is_valid      (const gchar *type_string);

Checks if type_string is a valid GVariant type string. This call is equivalent to calling g_variant_type_string_scan() and confirming that the following character is a nul terminator.

Since 2.24

g_variant_type_string_scan ()

gboolean            g_variant_type_string_scan          (const gchar *string,
                                                         const gchar *limit,
                                                         const gchar **endptr);

Scan for a single complete and valid GVariant type string in string. The memory pointed to by limit (or bytes beyond it) is never accessed.

If a valid type string is found, endptr is updated to point to the first character past the end of the string that was found and TRUE is returned.

If there is no valid type string starting at string, or if the type string does not end before limit then FALSE is returned.

For the simple case of checking if a string is a valid type string, see g_variant_type_string_is_valid().

Since 2.24

g_variant_type_get_string_length ()

gsize               g_variant_type_get_string_length    (const GVariantType *type);

Returns the length of the type string corresponding to the given type. This function must be used to determine the valid extent of the memory region returned by g_variant_type_peek_string().

Since 2.24

g_variant_type_peek_string ()

const gchar *       g_variant_type_peek_string          (const GVariantType *type);

Returns the type string corresponding to the given type. The result is not nul-terminated; in order to determine its length you must call g_variant_type_get_string_length().

To get a nul-terminated string, see g_variant_type_dup_string().

Since 2.24

g_variant_type_dup_string ()

gchar *             g_variant_type_dup_string           (const GVariantType *type);

Returns a newly-allocated copy of the type string corresponding to type. The returned string is nul-terminated. It is appropriate to call g_free() on the return value.

Since 2.24

g_variant_type_is_definite ()

gboolean            g_variant_type_is_definite          (const GVariantType *type);

Determines if the given type is definite (ie: not indefinite).

A type is definite if its type string does not contain any indefinite type characters ('*', '?', or 'r').

A GVariant instance may not have an indefinite type, so calling this function on the result of g_variant_get_type() will always result in TRUE being returned. Calling this function on an indefinite type like G_VARIANT_TYPE_ARRAY, however, will result in FALSE being returned.

Since 2.24

g_variant_type_is_container ()

gboolean            g_variant_type_is_container         (const GVariantType *type);

Determines if the given type is a container type.

Container types are any array, maybe, tuple, or dictionary entry types plus the variant type.

This function returns TRUE for any indefinite type for which every definite subtype is a container -- G_VARIANT_TYPE_ARRAY, for example.

Since 2.24

g_variant_type_is_basic ()

gboolean            g_variant_type_is_basic             (const GVariantType *type);

Determines if the given type is a basic type.

Basic types are booleans, bytes, integers, doubles, strings, object paths and signatures.

Only a basic type may be used as the key of a dictionary entry.

This function returns FALSE for all indefinite types except G_VARIANT_TYPE_BASIC.

Since 2.24

g_variant_type_is_maybe ()

gboolean            g_variant_type_is_maybe             (const GVariantType *type);

Determines if the given type is a maybe type. This is true if the type string for type starts with an 'm'.

This function returns TRUE for any indefinite type for which every definite subtype is a maybe type -- G_VARIANT_TYPE_MAYBE, for example.

Since 2.24

g_variant_type_is_array ()

gboolean            g_variant_type_is_array             (const GVariantType *type);

Determines if the given type is an array type. This is true if the type string for type starts with an 'a'.

This function returns TRUE for any indefinite type for which every definite subtype is an array type -- G_VARIANT_TYPE_ARRAY, for example.

Since 2.24

g_variant_type_is_tuple ()

gboolean            g_variant_type_is_tuple             (const GVariantType *type);

Determines if the given type is a tuple type. This is true if the type string for type starts with a '(' or if type is G_VARIANT_TYPE_TUPLE.

This function returns TRUE for any indefinite type for which every definite subtype is a tuple type -- G_VARIANT_TYPE_TUPLE, for example.

Since 2.24

g_variant_type_is_dict_entry ()

gboolean            g_variant_type_is_dict_entry        (const GVariantType *type);

Determines if the given type is a dictionary entry type. This is true if the type string for type starts with a '{'.

This function returns TRUE for any indefinite type for which every definite subtype is a dictionary entry type -- G_VARIANT_TYPE_DICT_ENTRY, for example.

Since 2.24

g_variant_type_is_variant ()

gboolean            g_variant_type_is_variant           (const GVariantType *type);

Determines if the given type is the variant type.

Since 2.24

g_variant_type_hash ()

guint               g_variant_type_hash                 (gconstpointer type);

Hashes type.

The argument type of type is only gconstpointer to allow use with GHashTable without function pointer casting. A valid GVariantType must be provided.

Since 2.24

g_variant_type_equal ()

gboolean            g_variant_type_equal                (gconstpointer type1,
                                                         gconstpointer type2);

Compares type1 and type2 for equality.

Only returns TRUE if the types are exactly equal. Even if one type is an indefinite type and the other is a subtype of it, FALSE will be returned if they are not exactly equal. If you want to check for subtypes, use g_variant_type_is_subtype_of().

The argument types of type1 and type2 are only gconstpointer to allow use with GHashTable without function pointer casting. For both arguments, a valid GVariantType must be provided.

Since 2.24

g_variant_type_is_subtype_of ()

gboolean            g_variant_type_is_subtype_of        (const GVariantType *type,
                                                         const GVariantType *supertype);

Checks if type is a subtype of supertype.

This function returns TRUE if type is a subtype of supertype. All types are considered to be subtypes of themselves. Aside from that, only indefinite types can have subtypes.

Since 2.24

g_variant_type_new_maybe ()

GVariantType *      g_variant_type_new_maybe            (const GVariantType *element);

Constructs the type corresponding to a maybe instance containing type type or Nothing.

It is appropriate to call g_variant_type_free() on the return value.

Since 2.24

g_variant_type_new_array ()

GVariantType *      g_variant_type_new_array            (const GVariantType *element);

Constructs the type corresponding to an array of elements of the type type.

It is appropriate to call g_variant_type_free() on the return value.

Since 2.24

g_variant_type_new_tuple ()

GVariantType *      g_variant_type_new_tuple            (const GVariantType * const *items,
                                                         gint length);

Constructs a new tuple type, from items.

length is the number of items in items, or -1 to indicate that items is NULL-terminated.

It is appropriate to call g_variant_type_free() on the return value.

Since 2.24

g_variant_type_new_dict_entry ()

GVariantType *      g_variant_type_new_dict_entry       (const GVariantType *key,
                                                         const GVariantType *value);

Constructs the type corresponding to a dictionary entry with a key of type key and a value of type value.

It is appropriate to call g_variant_type_free() on the return value.

Since 2.24

g_variant_type_element ()

const GVariantType * g_variant_type_element             (const GVariantType *type);

Determines the element type of an array or maybe type.

This function may only be used with array or maybe types.

Since 2.24

g_variant_type_n_items ()

gsize               g_variant_type_n_items              (const GVariantType *type);

Determines the number of items contained in a tuple or dictionary entry type.

This function may only be used with tuple or dictionary entry types, but must not be used with the generic tuple type G_VARIANT_TYPE_TUPLE.

In the case of a dictionary entry type, this function will always return 2.

Since 2.24

g_variant_type_first ()

const GVariantType * g_variant_type_first               (const GVariantType *type);

Determines the first item type of a tuple or dictionary entry type.

This function may only be used with tuple or dictionary entry types, but must not be used with the generic tuple type G_VARIANT_TYPE_TUPLE.

In the case of a dictionary entry type, this returns the type of the key.

NULL is returned in case of type being G_VARIANT_TYPE_UNIT.

This call, together with g_variant_type_next() provides an iterator interface over tuple and dictionary entry types.

Since 2.24

g_variant_type_next ()

const GVariantType * g_variant_type_next                (const GVariantType *type);

Determines the next item type of a tuple or dictionary entry type.

type must be the result of a previous call to g_variant_type_first() or g_variant_type_next().

If called on the key type of a dictionary entry then this call returns the value type. If called on the value type of a dictionary entry then this call returns NULL.

For tuples, NULL is returned when type is the last item in a tuple.

Since 2.24

g_variant_type_key ()

const GVariantType * g_variant_type_key                 (const GVariantType *type);

Determines the key type of a dictionary entry type.

This function may only be used with a dictionary entry type. Other than the additional restriction, this call is equivalent to g_variant_type_first().

Since 2.24

g_variant_type_value ()

const GVariantType * g_variant_type_value               (const GVariantType *type);

Determines the value type of a dictionary entry type.

This function may only be used with a dictionary entry type.

Since 2.24