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| GVariantType | |
| #define | G_VARIANT_TYPE_BOOLEAN |
| #define | G_VARIANT_TYPE_BYTE |
| #define | G_VARIANT_TYPE_INT16 |
| #define | G_VARIANT_TYPE_UINT16 |
| #define | G_VARIANT_TYPE_INT32 |
| #define | G_VARIANT_TYPE_UINT32 |
| #define | G_VARIANT_TYPE_INT64 |
| #define | G_VARIANT_TYPE_UINT64 |
| #define | G_VARIANT_TYPE_HANDLE |
| #define | G_VARIANT_TYPE_DOUBLE |
| #define | G_VARIANT_TYPE_STRING |
| #define | G_VARIANT_TYPE_OBJECT_PATH |
| #define | G_VARIANT_TYPE_SIGNATURE |
| #define | G_VARIANT_TYPE_VARIANT |
| #define | G_VARIANT_TYPE_ANY |
| #define | G_VARIANT_TYPE_BASIC |
| #define | G_VARIANT_TYPE_MAYBE |
| #define | G_VARIANT_TYPE_ARRAY |
| #define | G_VARIANT_TYPE_TUPLE |
| #define | G_VARIANT_TYPE_UNIT |
| #define | G_VARIANT_TYPE_DICT_ENTRY |
| #define | G_VARIANT_TYPE_DICTIONARY |
| #define | G_VARIANT_TYPE_STRING_ARRAY |
| #define | G_VARIANT_TYPE_OBJECT_PATH_ARRAY |
| #define | G_VARIANT_TYPE_BYTESTRING |
| #define | G_VARIANT_TYPE_BYTESTRING_ARRAY |
| #define | G_VARIANT_TYPE_VARDICT |
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).
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.
# define G_VARIANT_TYPE(type_string) (g_variant_type_checked_ ((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. If in doubt, use g_variant_type_string_is_valid() to
check if the string is valid.
Since 2.24
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
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.
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
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.
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
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().
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().
[skip]
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.
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.
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.
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.
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.
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.
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.
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.
gboolean
g_variant_type_is_variant (const GVariantType *type);
Determines if the given type
is the variant type.
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.
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.
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.
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.
[constructor]
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.
[constructor]
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.
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.
[constructor]
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.
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.
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.
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.
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().
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.
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_of(). May be copied using
g_variant_type_copy() and freed using g_variant_type_free().
#define G_VARIANT_TYPE_BYTE ((const GVariantType *) "y")
The type of an integer value that can range from 0 to 255.
#define G_VARIANT_TYPE_INT16 ((const GVariantType *) "n")
The type of an integer value that can range from -32768 to 32767.
#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.
#define G_VARIANT_TYPE_INT32 ((const GVariantType *) "i")
The type of an integer value that can range from -2147483648 to 2147483647.
#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.
#define G_VARIANT_TYPE_INT64 ((const GVariantType *) "x")
The type of an integer value that can range from -9223372036854775808 to 9223372036854775807.
#define G_VARIANT_TYPE_UINT64 ((const GVariantType *) "t")
The type of an integer value that can range from 0 to 18446744073709551615 (inclusive). That's a really big number, but a Rubik's cube can have a bit more than twice as many possible positions.
#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 D-Bus message.
If you are not interacting with D-Bus, then there is no reason to make use of this type.
#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.
#define G_VARIANT_TYPE_STRING ((const GVariantType *) "s")
The type of a string. "" is a string. NULL is not a string.
#define G_VARIANT_TYPE_OBJECT_PATH ((const GVariantType *) "o")
The type of a D-Bus 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 D-Bus, then there is no reason to make use of this type. If you are, then the D-Bus specification contains a precise description of valid object paths.
#define G_VARIANT_TYPE_SIGNATURE ((const GVariantType *) "g")
The type of a D-Bus type signature. These are strings of a specific format used as type signatures for D-Bus methods and messages.
If you are not interacting with D-Bus, then there is no reason to make use of this type. If you are, then the D-Bus specification contains a precise description of valid signature strings.
#define G_VARIANT_TYPE_VARIANT ((const GVariantType *) "v")
The type of a box that contains any other value (including another variant).
#define G_VARIANT_TYPE_ANY ((const GVariantType *) "*")
An indefinite type that is a supertype of every type (including itself).
#define G_VARIANT_TYPE_BASIC ((const GVariantType *) "?")
An indefinite type that is a supertype of every basic (ie: non-container) type.
#define G_VARIANT_TYPE_MAYBE ((const GVariantType *) "m*")
An indefinite type that is a supertype of every maybe type.
#define G_VARIANT_TYPE_ARRAY ((const GVariantType *) "a*")
An indefinite type that is a supertype of every array type.
#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.
#define G_VARIANT_TYPE_UNIT ((const GVariantType *) "()")
The empty tuple type. Has only one instance. Known also as "triv" or "void".
#define G_VARIANT_TYPE_DICT_ENTRY ((const GVariantType *) "{?*}")
An indefinite type that is a supertype of every dictionary entry type.
#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.
#define G_VARIANT_TYPE_STRING_ARRAY ((const GVariantType *) "as")
The type of an array of strings.
#define G_VARIANT_TYPE_OBJECT_PATH_ARRAY ((const GVariantType *) "ao")
The type of an array of object paths.
#define G_VARIANT_TYPE_BYTESTRING ((const GVariantType *) "ay")
The type of an array of bytes. This type is commonly used to pass around strings that may not be valid utf8. In that case, the convention is that the nul terminator character should be included as the last character in the array.
#define G_VARIANT_TYPE_BYTESTRING_ARRAY ((const GVariantType *) "aay")
The type of an array of byte strings (an array of arrays of bytes).
#define G_VARIANT_TYPE_VARDICT ((const GVariantType *) "a{sv}")
The type of a dictionary mapping strings to variants (the ubiquitous "a{sv}" type).
Since: 2.30