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.
a valid GVariant type string
Makes a copy of a #GVariantType. It is appropriate to call
g_variant_type_free() on the return value. type may not be %NULL.
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.
Determines the element type of an array or maybe type.
This function may only be used with array or maybe types.
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.
a #GVariantType
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.
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
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().
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.
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.
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.
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.
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.
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.
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.
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.
a #GVariantType
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.
Determines if the given type is the variant 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().
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.
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.
Determines the value type of a dictionary entry type.
This function may only be used with a dictionary entry type.
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.
a valid GVariant type string
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.
a #GVariantType
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.
a basic #GVariantType
a #GVariantType
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.
a #GVariantType
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.
an array of #GVariantTypes, one for each item
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.
a pointer to any string
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().
a pointer to any string
the end of string, or %NULL
This section introduces the GVariant type system. It is based, in large part, on the D-Bus type system, with two major changes and some minor lifting of restrictions. The D-Bus specification, therefore, provides a significant amount of information that is useful when working with GVariant.
The first major change with respect to the D-Bus type system is the introduction of maybe (or "nullable") types. Any type in GVariant can be converted to a maybe type, in which case, "nothing" (or "null") becomes a valid value. Maybe types have been added by introducing the character "m" to type strings.
The second major change is that the GVariant type system supports the concept of "indefinite types" -- types that are less specific than the normal types found in D-Bus. For example, it is possible to speak of "an array of any type" in GVariant, where the D-Bus type system would require you to speak of "an array of integers" or "an array of strings". Indefinite types have been added by introducing the characters "*", "?" and "r" to type strings.
Finally, all arbitrary restrictions relating to the complexity of types are lifted along with the restriction that dictionary entries may only appear nested inside of arrays.
Just as in D-Bus, GVariant types are described with strings ("type strings"). Subject to the differences mentioned above, these strings are of the same form as those found in D-Bus. Note, however: D-Bus always works in terms of messages and therefore individual type strings appear nowhere in its interface. Instead, "signatures" are a concatenation of the strings of the type of each argument in a message. GVariant deals with single values directly so GVariant type strings always describe the type of exactly one value. This means that a D-Bus signature string is generally not a valid GVariant type string -- except in the case that it is the signature of a message containing exactly one argument.
An indefinite type is similar in spirit to what may be called an abstract type in other type systems. No value can exist that has an indefinite type as its type, but values can exist that have types that are subtypes of indefinite types. That is to say, g_variant_get_type() will never return an indefinite type, but calling g_variant_is_of_type() with an indefinite type may return %TRUE. For example, you cannot have a value that represents "an array of no particular type", but you can have an "array of integers" which certainly matches the type of "an array of no particular type", since "array of integers" is a subtype of "array of no particular type".
This is similar to how instances of abstract classes may not directly exist in other type systems, but instances of their non-abstract subtypes may. For example, in GTK, no object that has the type of #GtkBin can exist (since #GtkBin is an abstract class), but a #GtkWindow can certainly be instantiated, and you would say that the #GtkWindow is a #GtkBin (since #GtkWindow is a subclass of #GtkBin).
GVariant Type Strings
A GVariant type string can be any of the following:
any basic type string (listed below)
"v", "r" or "*"
one of the characters 'a' or 'm', followed by another type string
the character '(', followed by a concatenation of zero or more other type strings, followed by the character ')'
the character '{', followed by a basic type string (see below), followed by another type string, followed by the character '}'
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)}))". In order to not hit memory limits, #GVariant imposes a limit on recursion depth of 65 nested containers. This is the limit in the D-Bus specification (64) plus one to allow a #GDBusMessage to be nested in a top-level tuple.
The meaning of each of the characters is as follows:
b: the type string of %G_VARIANT_TYPE_BOOLEAN; a boolean value.y: the type string of %G_VARIANT_TYPE_BYTE; a byte.n: the type string of %G_VARIANT_TYPE_INT16; a signed 16 bit integer.q: the type string of %G_VARIANT_TYPE_UINT16; an unsigned 16 bit integer.i: the type string of %G_VARIANT_TYPE_INT32; a signed 32 bit integer.u: the type string of %G_VARIANT_TYPE_UINT32; an unsigned 32 bit integer.x: the type string of %G_VARIANT_TYPE_INT64; a signed 64 bit integer.t: the type string of %G_VARIANT_TYPE_UINT64; an unsigned 64 bit integer.h: the type string of %G_VARIANT_TYPE_HANDLE; a signed 32 bit value that, by convention, is used as an index into an array of file descriptors that are sent alongside a D-Bus message.d: the type string of %G_VARIANT_TYPE_DOUBLE; a double precision floating point value.s: the type string of %G_VARIANT_TYPE_STRING; a string.o: the type string of %G_VARIANT_TYPE_OBJECT_PATH; a string in the form of a D-Bus object path.g: the type string of %G_VARIANT_TYPE_SIGNATURE; a string in the form of a D-Bus type signature.?: the type string of %G_VARIANT_TYPE_BASIC; an indefinite type that is a supertype of any of the basic types.v: the type string of %G_VARIANT_TYPE_VARIANT; a container type that contain any other type of value.a: used as a prefix on another type string to mean an array of that type; the type string "ai", for example, is the type of an array of signed 32-bit integers.m: used as a prefix on another type string to mean a "maybe", or "nullable", version of that type; the type string "ms", for example, is the type of a value that maybe contains a string, or maybe contains nothing.(): used to enclose zero or more other concatenated type strings to create a tuple type; the type string "(is)", for example, is the type of a pair of an integer and a string.r: the type string of %G_VARIANT_TYPE_TUPLE; an indefinite type that is a supertype of any tuple type, regardless of the number of items.{}: used to enclose a basic type string concatenated with another type string to create a dictionary entry type, which usually appears inside of an array to form a dictionary; the type string "a{sd}", for example, is the type of a dictionary that maps strings to double precision floating point values.The first type (the basic type) is the key type and the second type is the value type. The reason that the first type is restricted to being a basic type is so that it can easily be hashed.
*: the type string of %G_VARIANT_TYPE_ANY; the indefinite type that is a supertype of all types. Note that, as with all type strings, this character represents exactly one type. It cannot be used inside of tuples to mean "any number of items".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.