GVariant

GVariant — strongly typed value datatype

Synopsis

#include <glib.h>

                    GVariant;
void                g_variant_unref                     (GVariant *value);
GVariant *          g_variant_ref                       (GVariant *value);
GVariant *          g_variant_ref_sink                  (GVariant *value);
const GVariantType * g_variant_get_type                 (GVariant *value);
const gchar *       g_variant_get_type_string           (GVariant *value);
gboolean            g_variant_is_of_type                (GVariant *value,
                                                         const GVariantType *type);
gboolean            g_variant_is_container              (GVariant *value);

GVariantClass       g_variant_classify                  (GVariant *value);
enum                GVariantClass;

GVariant *          g_variant_new_boolean               (gboolean boolean);
GVariant *          g_variant_new_byte                  (guchar byte);
GVariant *          g_variant_new_int16                 (gint16 int16);
GVariant *          g_variant_new_uint16                (guint16 uint16);
GVariant *          g_variant_new_int32                 (gint32 int32);
GVariant *          g_variant_new_uint32                (guint32 uint32);
GVariant *          g_variant_new_int64                 (gint64 int64);
GVariant *          g_variant_new_uint64                (guint64 uint64);
GVariant *          g_variant_new_handle                (gint32 handle);
GVariant *          g_variant_new_double                (gdouble floating);
GVariant *          g_variant_new_string                (const gchar *string);
GVariant *          g_variant_new_object_path           (const gchar *object_path);
gboolean            g_variant_is_object_path            (const gchar *string);
GVariant *          g_variant_new_signature             (const gchar *signature);
gboolean            g_variant_is_signature              (const gchar *string);
GVariant *          g_variant_new_variant               (GVariant *value);
GVariant *          g_variant_new_strv                  (const gchar * const *strv,
                                                         gssize length);

gboolean            g_variant_get_boolean               (GVariant *value);
guchar              g_variant_get_byte                  (GVariant *value);
gint16              g_variant_get_int16                 (GVariant *value);
guint16             g_variant_get_uint16                (GVariant *value);
gint32              g_variant_get_int32                 (GVariant *value);
guint32             g_variant_get_uint32                (GVariant *value);
gint64              g_variant_get_int64                 (GVariant *value);
guint64             g_variant_get_uint64                (GVariant *value);
gint32              g_variant_get_handle                (GVariant *value);
gdouble             g_variant_get_double                (GVariant *value);
const gchar *       g_variant_get_string                (GVariant *value,
                                                         gsize *length);
gchar *             g_variant_dup_string                (GVariant *value,
                                                         gsize *length);
GVariant *          g_variant_get_variant               (GVariant *value);
const gchar **      g_variant_get_strv                  (GVariant *value,
                                                         gsize *length);
gchar **            g_variant_dup_strv                  (GVariant *value,
                                                         gsize *length);

GVariant *          g_variant_new_maybe                 (const GVariantType *child_type,
                                                         GVariant *child);
GVariant *          g_variant_new_array                 (const GVariantType *child_type,
                                                         GVariant * const *children,
                                                         gsize n_children);
GVariant *          g_variant_new_tuple                 (GVariant * const *children,
                                                         gsize n_children);
GVariant *          g_variant_new_dict_entry            (GVariant *key,
                                                         GVariant *value);

GVariant *          g_variant_get_maybe                 (GVariant *value);
gsize               g_variant_n_children                (GVariant *value);
GVariant *          g_variant_get_child_value           (GVariant *value,
                                                         gsize index_);
gconstpointer       g_variant_get_fixed_array           (GVariant *value,
                                                         gsize *n_elements,
                                                         gsize element_size);

gsize               g_variant_get_size                  (GVariant *value);
gconstpointer       g_variant_get_data                  (GVariant *value);
void                g_variant_store                     (GVariant *value,
                                                         gpointer data);

guint               g_variant_hash                      (gconstpointer value);
gboolean            g_variant_equal                     (gconstpointer one,
                                                         gconstpointer two);

gchar *             g_variant_print                     (GVariant *value,
                                                         gboolean type_annotate);
GString *           g_variant_print_string              (GVariant *value,
                                                         GString *string,
                                                         gboolean type_annotate);

Description

GVariant is a variant datatype; it stores a value along with information about the type of that value. The range of possible values is determined by the type. The type system used by GVariant is GVariantType.

GVariant instances always have a type and a value (which are given at construction time). The type and value of a GVariant instance can never change other than by the GVariant itself being destroyed. A GVariant can not contain a pointer.

GVariant is reference counted using g_variant_ref() and g_variant_unref(). GVariant also has floating reference counts -- see g_variant_ref_sink().

GVariant is completely threadsafe. A GVariant instance can be concurrently accessed in any way from any number of threads without problems.

GVariant is heavily optimised for dealing with data in serialised form. It works particularly well with data located in memory-mapped files. It can perform nearly all deserialisation operations in a small constant time, usually touching only a single memory page. Serialised GVariant data can also be sent over the network.

GVariant is largely compatible with DBus. Almost all types of GVariant instances can be sent over DBus. See GVariantType for exceptions.

For convenience to C programmers, GVariant features powerful varargs-based value construction and destruction. This feature is designed to be embedded in other libraries.

There is a Python-inspired text language for describing GVariant values. GVariant includes a printer for this language and a parser with type inferencing.

Memory Use

GVariant tries to be quite efficient with respect to memory use. This section gives a rough idea of how much memory is used by the current implementation. The information here is subject to change in the future.

The memory allocated by GVariant can be grouped into 4 broad purposes: memory for serialised data, memory for the type information cache, buffer management memory and memory for the GVariant structure itself.

Serialised Data Memory

This is the memory that is used for storing GVariant data in serialised form. This is what would be sent over the network or what would end up on disk.

The amount of memory required to store a boolean is 1 byte. 16, 32 and 64 bit integers and double precision floating point numbers use their "natural" size. Strings (including object path and signature strings) are stored with a nul terminator, and as such use the length of the string plus 1 byte.

Maybe types use no space at all to represent the null value and use the same amount of space (sometimes plus one byte) as the equivalent non-maybe-typed value to represent the non-null case.

Arrays use the amount of space required to store each of their members, concatenated. Additionally, if the items stored in an array are not of a fixed-size (ie: strings, other arrays, etc) then an additional framing offset is stored for each item. The size of this offset is either 1, 2 or 4 bytes depending on the overall size of the container. Additionally, extra padding bytes are added as required for alignment of child values.

Tuples (including dictionary entries) use the amount of space required to store each of their members, concatenated, plus one framing offset (as per arrays) for each non-fixed-sized item in the tuple, except for the last one. Additionally, extra padding bytes are added as required for alignment of child values.

Variants use the same amount of space as the item inside of the variant, plus 1 byte, plus the length of the type string for the item inside the variant.

As an example, consider a dictionary mapping strings to variants. In the case that the dictionary is empty, 0 bytes are required for the serialisation.

If we add an item "width" that maps to the int32 value of 500 then we will use 4 byte to store the int32 (so 6 for the variant containing it) and 6 bytes for the string. The variant must be aligned to 8 after the 6 bytes of the string, so that's 2 extra bytes. 6 (string) + 2 (padding) + 6 (variant) is 14 bytes used for the dictionary entry. An additional 1 byte is added to the array as a framing offset making a total of 15 bytes.

If we add another entry, "title" that maps to a nullable string that happens to have a value of null, then we use 0 bytes for the null value (and 3 bytes for the variant to contain it along with its type string) plus 6 bytes for the string. Again, we need 2 padding bytes. That makes a total of 6 + 2 + 3 = 11 bytes.

We now require extra padding between the two items in the array. After the 14 bytes of the first item, that's 2 bytes required. We now require 2 framing offsets for an extra two bytes. 14 + 2 + 11 + 2 = 29 bytes to encode the entire two-item dictionary.

Type Information Cache

For each GVariant type that currently exists in the program a type information structure is kept in the type information cache. The type information structure is required for rapid deserialisation.

Continuing with the above example, if a GVariant exists with the type "a{sv}" then a type information struct will exist for "a{sv}", "{sv}", "s", and "v". Multiple uses of the same type will share the same type information. Additionally, all single-digit types are stored in read-only static memory and do not contribute to the writable memory footprint of a program using GVariant.

Aside from the type information structures stored in read-only memory, there are two forms of type information. One is used for container types where there is a single element type: arrays and maybe types. The other is used for container types where there are multiple element types: tuples and dictionary entries.

Array type info structures are 6 * sizeof (void *), plus the memory required to store the type string itself. This means that on 32bit systems, the cache entry for "a{sv}" would require 30 bytes of memory (plus malloc overhead).

Tuple type info structures are 6 * sizeof (void *), plus 4 * sizeof (void *) for each item in the tuple, plus the memory required to store the type string itself. A 2-item tuple, for example, would have a type information structure that consumed writable memory in the size of 14 * sizeof (void *) (plus type string) This means that on 32bit systems, the cache entry for "{sv}" would require 61 bytes of memory (plus malloc overhead).

This means that in total, for our "a{sv}" example, 91 bytes of type information would be allocated.

The type information cache, additionally, uses a GHashTable to store and lookup the cached items and stores a pointer to this hash table in static storage. The hash table is freed when there are zero items in the type cache.

Although these sizes may seem large it is important to remember that a program will probably only have a very small number of different types of values in it and that only one type information structure is required for many different values of the same type.

Buffer Management Memory

GVariant uses an internal buffer management structure to deal with the various different possible sources of serialised data that it uses. The buffer is responsible for ensuring that the correct call is made when the data is no longer in use by GVariant. This may involve a g_free() or a g_slice_free() or even g_mapped_file_unref().

One buffer management structure is used for each chunk of serialised data. The size of the buffer management structure is 4 * (void *). On 32bit systems, that's 16 bytes.

GVariant structure

The size of a GVariant structure is 6 * (void *). On 32 bit systems, that's 24 bytes.

GVariant structures only exist if they are explicitly created with API calls. For example, if a GVariant is constructed out of serialised data for the example given above (with the dictionary) then although there are 9 individual values that comprise the entire dictionary (two keys, two values, two variants containing the values, two dictionary entries, plus the dictionary itself), only 1 GVariant instance exists -- the one refering to the dictionary.

If calls are made to start accessing the other values then GVariant instances will exist for those values only for as long as they are in use (ie: until you call g_variant_unref()). The type information is shared. The serialised data and the buffer management structure for that serialised data is shared by the child.

Summary

To put the entire example together, for our dictionary mapping strings to variants (with two entries, as given above), we are using 91 bytes of memory for type information, 29 byes of memory for the serialised data, 16 bytes for buffer management and 24 bytes for the GVariant instance, or a total of 160 bytes, plus malloc overhead. If we were to use g_variant_get_child_value() to access the two dictionary entries, we would use an additional 48 bytes. If we were to have other dictionaries of the same type, we would use more memory for the serialised data and buffer management for those dictionaries, but the type information would be shared.

Details

GVariant

typedef struct _GVariant GVariant;

GVariant is an opaque data structure and can only be accessed using the following functions.

Since 2.24


g_variant_unref ()

void                g_variant_unref                     (GVariant *value);

Decreases the reference count of value. When its reference count drops to 0, the memory used by the variant is freed.

value :

a GVariant

Since 2.24


g_variant_ref ()

GVariant *          g_variant_ref                       (GVariant *value);

Increases the reference count of value.

value :

a GVariant

Returns :

the same value

Since 2.24


g_variant_ref_sink ()

GVariant *          g_variant_ref_sink                  (GVariant *value);

GVariant uses a floating reference count system. All functions with names starting with g_variant_new_ return floating references.

Calling g_variant_ref_sink() on a GVariant with a floating reference will convert the floating reference into a full reference. Calling g_variant_ref_sink() on a non-floating GVariant results in an additional normal reference being added.

In other words, if the value is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference. If the value is not floating, then this call adds a new normal reference increasing the reference count by one.

All calls that result in a GVariant instance being inserted into a container will call g_variant_ref_sink() on the instance. This means that if the value was just created (and has only its floating reference) then the container will assume sole ownership of the value at that point and the caller will not need to unreference it. This makes certain common styles of programming much easier while still maintaining normal refcounting semantics in situations where values are not floating.

value :

a GVariant

Returns :

the same value

Since 2.24


g_variant_get_type ()

const GVariantType * g_variant_get_type                 (GVariant *value);

Determines the type of value.

The return value is valid for the lifetime of value and must not be freed.

value :

a GVariant

Returns :

a GVariantType

Since 2.24


g_variant_get_type_string ()

const gchar *       g_variant_get_type_string           (GVariant *value);

Returns the type string of value. Unlike the result of calling g_variant_type_peek_string(), this string is nul-terminated. This string belongs to GVariant and must not be freed.

value :

a GVariant

Returns :

the type string for the type of value

Since 2.24


g_variant_is_of_type ()

gboolean            g_variant_is_of_type                (GVariant *value,
                                                         const GVariantType *type);

Checks if a value has a type matching the provided type.

value :

a GVariant instance

type :

a GVariantType

Returns :

TRUE if the type of value matches type

Since 2.24


g_variant_is_container ()

gboolean            g_variant_is_container              (GVariant *value);

Checks if value is a container.

value :

a GVariant instance

Returns :

TRUE if value is a container

g_variant_classify ()

GVariantClass       g_variant_classify                  (GVariant *value);

Classifies value according to its top-level type.

value :

a GVariant

Returns :

the GVariantClass of value

Since 2.24


enum GVariantClass

typedef enum
{
  G_VARIANT_CLASS_BOOLEAN       = 'b',
  G_VARIANT_CLASS_BYTE          = 'y',
  G_VARIANT_CLASS_INT16         = 'n',
  G_VARIANT_CLASS_UINT16        = 'q',
  G_VARIANT_CLASS_INT32         = 'i',
  G_VARIANT_CLASS_UINT32        = 'u',
  G_VARIANT_CLASS_INT64         = 'x',
  G_VARIANT_CLASS_UINT64        = 't',
  G_VARIANT_CLASS_HANDLE        = 'h',
  G_VARIANT_CLASS_DOUBLE        = 'd',
  G_VARIANT_CLASS_STRING        = 's',
  G_VARIANT_CLASS_OBJECT_PATH   = 'o',
  G_VARIANT_CLASS_SIGNATURE     = 'g',
  G_VARIANT_CLASS_VARIANT       = 'v',
  G_VARIANT_CLASS_MAYBE         = 'm',
  G_VARIANT_CLASS_ARRAY         = 'a',
  G_VARIANT_CLASS_TUPLE         = '(',
  G_VARIANT_CLASS_DICT_ENTRY    = '{'
} GVariantClass;

The range of possible top-level types of GVariant instances.

G_VARIANT_CLASS_BOOLEAN

The GVariant is a boolean.

G_VARIANT_CLASS_BYTE

The GVariant is a byte.

G_VARIANT_CLASS_INT16

The GVariant is a signed 16 bit integer.

G_VARIANT_CLASS_UINT16

The GVariant is an unsigned 16 bit integer.

G_VARIANT_CLASS_INT32

The GVariant is a signed 32 bit integer.

G_VARIANT_CLASS_UINT32

The GVariant is an unsigned 32 bit integer.

G_VARIANT_CLASS_INT64

The GVariant is a signed 64 bit integer.

G_VARIANT_CLASS_UINT64

The GVariant is an unsigned 64 bit integer.

G_VARIANT_CLASS_HANDLE

The GVariant is a file handle index.

G_VARIANT_CLASS_DOUBLE

The GVariant is a double precision floating point value.

G_VARIANT_CLASS_STRING

The GVariant is a normal string.

G_VARIANT_CLASS_OBJECT_PATH

The GVariant is a DBus object path string.

G_VARIANT_CLASS_SIGNATURE

The GVariant is a DBus signature string.

G_VARIANT_CLASS_VARIANT

The GVariant is a variant.

G_VARIANT_CLASS_MAYBE

The GVariant is a maybe-typed value.

G_VARIANT_CLASS_ARRAY

The GVariant is an array.

G_VARIANT_CLASS_TUPLE

The GVariant is a tuple.

G_VARIANT_CLASS_DICT_ENTRY

The GVariant is a dictionary entry.

Since 2.24


g_variant_new_boolean ()

GVariant *          g_variant_new_boolean               (gboolean boolean);

Creates a new boolean GVariant instance -- either TRUE or FALSE.

boolean :

a gboolean value

Returns :

a new boolean GVariant instance

Since 2.24


g_variant_new_byte ()

GVariant *          g_variant_new_byte                  (guchar byte);

Creates a new byte GVariant instance.

byte :

a guint8 value

Returns :

a new byte GVariant instance

Since 2.24


g_variant_new_int16 ()

GVariant *          g_variant_new_int16                 (gint16 int16);

Creates a new int16 GVariant instance.

int16 :

a gint16 value

Returns :

a new int16 GVariant instance

Since 2.24


g_variant_new_uint16 ()

GVariant *          g_variant_new_uint16                (guint16 uint16);

Creates a new uint16 GVariant instance.

uint16 :

a guint16 value

Returns :

a new uint16 GVariant instance

Since 2.24


g_variant_new_int32 ()

GVariant *          g_variant_new_int32                 (gint32 int32);

Creates a new int32 GVariant instance.

int32 :

a gint32 value

Returns :

a new int32 GVariant instance

Since 2.24


g_variant_new_uint32 ()

GVariant *          g_variant_new_uint32                (guint32 uint32);

Creates a new uint32 GVariant instance.

uint32 :

a guint32 value

Returns :

a new uint32 GVariant instance

Since 2.24


g_variant_new_int64 ()

GVariant *          g_variant_new_int64                 (gint64 int64);

Creates a new int64 GVariant instance.

int64 :

a gint64 value

Returns :

a new int64 GVariant instance

Since 2.24


g_variant_new_uint64 ()

GVariant *          g_variant_new_uint64                (guint64 uint64);

Creates a new uint64 GVariant instance.

uint64 :

a guint64 value

Returns :

a new uint64 GVariant instance

Since 2.24


g_variant_new_handle ()

GVariant *          g_variant_new_handle                (gint32 handle);

Creates a new handle GVariant instance.

By convention, handles are indexes into an array of file descriptors that are sent alongside a DBus message. If you're not interacting with DBus, you probably don't need them.

handle :

a gint32 value

Returns :

a new handle GVariant instance

Since 2.24


g_variant_new_double ()

GVariant *          g_variant_new_double                (gdouble floating);

Creates a new double GVariant instance.

floating :

a gdouble floating point value

Returns :

a new double GVariant instance

Since 2.24


g_variant_new_string ()

GVariant *          g_variant_new_string                (const gchar *string);

Creates a string GVariant with the contents of string.

string :

a normal C nul-terminated string

Returns :

a new string GVariant instance

Since 2.24


g_variant_new_object_path ()

GVariant *          g_variant_new_object_path           (const gchar *object_path);

Creates a DBus object path GVariant with the contents of string. string must be a valid DBus object path. Use g_variant_is_object_path() if you're not sure.

object_path :

a normal C nul-terminated string

Returns :

a new object path GVariant instance

Since 2.24


g_variant_is_object_path ()

gboolean            g_variant_is_object_path            (const gchar *string);

Determines if a given string is a valid DBus object path. You should ensure that a string is a valid DBus object path before passing it to g_variant_new_object_path().

A valid object path starts with '/' followed by zero or more sequences of characters separated by '/' characters. Each sequence must contain only the characters "[A-Z][a-z][0-9]_". No sequence (including the one following the final '/' character) may be empty.

string :

a normal C nul-terminated string

Returns :

TRUE if string is a DBus object path

Since 2.24


g_variant_new_signature ()

GVariant *          g_variant_new_signature             (const gchar *signature);

Creates a DBus type signature GVariant with the contents of string. string must be a valid DBus type signature. Use g_variant_is_signature() if you're not sure.

signature :

a normal C nul-terminated string

Returns :

a new signature GVariant instance

Since 2.24


g_variant_is_signature ()

gboolean            g_variant_is_signature              (const gchar *string);

Determines if a given string is a valid DBus type signature. You should ensure that a string is a valid DBus object path before passing it to g_variant_new_signature().

DBus type signatures consist of zero or more definite GVariantType strings in sequence.

string :

a normal C nul-terminated string

Returns :

TRUE if string is a DBus type signature

Since 2.24


g_variant_new_variant ()

GVariant *          g_variant_new_variant               (GVariant *value);

Boxes value. The result is a GVariant instance representing a variant containing the original value.

value :

a GVariance instance

Returns :

a new variant GVariant instance

Since 2.24


g_variant_new_strv ()

GVariant *          g_variant_new_strv                  (const gchar * const *strv,
                                                         gssize length);

Constructs an array of strings GVariant from the given array of strings.

If length is not -1 then it gives the maximum length of strv. In any case, a NULL pointer in strv is taken as a terminator.

strv :

an array of strings

length :

the length of strv, or -1

Returns :

a new floating GVariant instance

Since 2.24


g_variant_get_boolean ()

gboolean            g_variant_get_boolean               (GVariant *value);

Returns the boolean value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_BOOLEAN.

value :

a boolean GVariant instance

Returns :

TRUE or FALSE

Since 2.24


g_variant_get_byte ()

guchar              g_variant_get_byte                  (GVariant *value);

Returns the byte value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_BYTE.

value :

a byte GVariant instance

Returns :

a guchar

Since 2.24


g_variant_get_int16 ()

gint16              g_variant_get_int16                 (GVariant *value);

Returns the 16-bit signed integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_INT16.

value :

a int16 GVariant instance

Returns :

a gint16

Since 2.24


g_variant_get_uint16 ()

guint16             g_variant_get_uint16                (GVariant *value);

Returns the 16-bit unsigned integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_UINT16.

value :

a uint16 GVariant instance

Returns :

a guint16

Since 2.24


g_variant_get_int32 ()

gint32              g_variant_get_int32                 (GVariant *value);

Returns the 32-bit signed integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_INT32.

value :

a int32 GVariant instance

Returns :

a gint32

Since 2.24


g_variant_get_uint32 ()

guint32             g_variant_get_uint32                (GVariant *value);

Returns the 32-bit unsigned integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_UINT32.

value :

a uint32 GVariant instance

Returns :

a guint32

Since 2.24


g_variant_get_int64 ()

gint64              g_variant_get_int64                 (GVariant *value);

Returns the 64-bit signed integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_INT64.

value :

a int64 GVariant instance

Returns :

a gint64

Since 2.24


g_variant_get_uint64 ()

guint64             g_variant_get_uint64                (GVariant *value);

Returns the 64-bit unsigned integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_UINT64.

value :

a uint64 GVariant instance

Returns :

a guint64

Since 2.24


g_variant_get_handle ()

gint32              g_variant_get_handle                (GVariant *value);

Returns the 32-bit signed integer value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_HANDLE.

By convention, handles are indexes into an array of file descriptors that are sent alongside a DBus message. If you're not interacting with DBus, you probably don't need them.

value :

a handle GVariant instance

Returns :

a gint32

Since 2.24


g_variant_get_double ()

gdouble             g_variant_get_double                (GVariant *value);

Returns the double precision floating point value of value.

It is an error to call this function with a value of any type other than G_VARIANT_TYPE_DOUBLE.

value :

a double GVariant instance

Returns :

a gdouble

Since 2.24


g_variant_get_string ()

const gchar *       g_variant_get_string                (GVariant *value,
                                                         gsize *length);

Returns the string value of a GVariant instance with a string type. This includes the types G_VARIANT_TYPE_STRING, G_VARIANT_TYPE_OBJECT_PATH and G_VARIANT_TYPE_SIGNATURE.

If length is non-NULL then the length of the string (in bytes) is returned there. For trusted values, this information is already known. For untrusted values, a strlen() will be performed.

It is an error to call this function with a value of any type other than those three.

The return value remains valid as long as value exists.

value :

a string GVariant instance

length :

a pointer to a gsize, to store the length

Returns :

the constant string

Since 2.24


g_variant_dup_string ()

gchar *             g_variant_dup_string                (GVariant *value,
                                                         gsize *length);

Similar to g_variant_get_string() except that instead of returning a constant string, the string is duplicated.

The return value must be freed using g_free().

value :

a string GVariant instance

length :

a pointer to a gsize, to store the length

Returns :

a newly allocated string

Since 2.24


g_variant_get_variant ()

GVariant *          g_variant_get_variant               (GVariant *value);

Unboxes value. The result is the GVariant instance that was contained in value.

value :

a variant GVariance instance

Returns :

the item contained in the variant

Since 2.24


g_variant_get_strv ()

const gchar **      g_variant_get_strv                  (GVariant *value,
                                                         gsize *length);

Gets the contents of an array of strings GVariant. This call makes a shallow copy; the return result should be released with g_free(), but the individual strings must not be modified.

If length is non-NULL then the number of elements in the result is stored there. In any case, the resulting array will be NULL-terminated.

For an empty array, length will be set to 0 and a pointer to a NULL pointer will be returned.

value :

an array of strings GVariant

length :

the length of the result, or NULL

Returns :

an array of constant strings

Since 2.24


g_variant_dup_strv ()

gchar **            g_variant_dup_strv                  (GVariant *value,
                                                         gsize *length);

Gets the contents of an array of strings GVariant. This call makes a deep copy; the return result should be released with g_strfreev().

If length is non-NULL then the number of elements in the result is stored there. In any case, the resulting array will be NULL-terminated.

For an empty array, length will be set to 0 and a pointer to a NULL pointer will be returned.

value :

an array of strings GVariant

length :

the length of the result, or NULL

Returns :

an array of constant strings

Since 2.24


g_variant_new_maybe ()

GVariant *          g_variant_new_maybe                 (const GVariantType *child_type,
                                                         GVariant *child);

Depending on if value is NULL, either wraps value inside of a maybe container or creates a Nothing instance for the given type.

At least one of type and value must be non-NULL. If type is non-NULL then it must be a definite type. If they are both non-NULL then type must be the type of value.

child_type :

the GVariantType of the child

child :

the child value, or NULL

Returns :

a new GVariant maybe instance

Since 2.24


g_variant_new_array ()

GVariant *          g_variant_new_array                 (const GVariantType *child_type,
                                                         GVariant * const *children,
                                                         gsize n_children);

Creates a new GVariant array from children.

child_type must be non-NULL if n_children is zero. Otherwise, the child type is determined by inspecting the first element of the children array. If child_type is non-NULL then it must be a definite type.

The items of the array are taken from the children array. No entry in the children array may be NULL.

All items in the array must have the same type, which must be the same as child_type, if given.

child_type :

the element type of the new array

children :

an array of GVariant pointers, the children

n_children :

the length of children

Returns :

a new GVariant array

Since 2.24


g_variant_new_tuple ()

GVariant *          g_variant_new_tuple                 (GVariant * const *children,
                                                         gsize n_children);

Creates a new tuple GVariant out of the items in children. The type is determined from the types of children. No entry in the children array may be NULL.

If n_children is 0 then the unit tuple is constructed.

children :

the items to make the tuple out of

n_children :

the length of children

Returns :

a new GVariant tuple

Since 2.24


g_variant_new_dict_entry ()

GVariant *          g_variant_new_dict_entry            (GVariant *key,
                                                         GVariant *value);

Creates a new dictionary entry GVariant. key and value must be non-NULL.

key must be a value of a basic type (ie: not a container).

key :

a basic GVariant, the key

value :

a GVariant, the value

Returns :

a new dictionary entry GVariant

Since 2.24


g_variant_get_maybe ()

GVariant *          g_variant_get_maybe                 (GVariant *value);

Given a maybe-typed GVariant instance, extract its value. If the value is Nothing, then this function returns NULL.

value :

a maybe-typed value

Returns :

the contents of value, or NULL

Since 2.24


g_variant_n_children ()

gsize               g_variant_n_children                (GVariant *value);

Determines the number of children in a container GVariant instance. This includes variants, maybes, arrays, tuples and dictionary entries. It is an error to call this function on any other type of GVariant.

For variants, the return value is always 1. For values with maybe types, it is always zero or one. For arrays, it is the length of the array. For tuples it is the number of tuple items (which depends only on the type). For dictionary entries, it is always 2

This function is O(1).

value :

a container GVariant

Returns :

the number of children in the container

Since 2.24


g_variant_get_child_value ()

GVariant *          g_variant_get_child_value           (GVariant *value,
                                                         gsize index_);

Reads a child item out of a container GVariant instance. This includes variants, maybes, arrays, tuples and dictionary entries. It is an error to call this function on any other type of GVariant.

It is an error if index_ is greater than the number of child items in the container. See g_variant_n_children().

This function is O(1).

value :

a container GVariant

index_ :

the index of the child to fetch

Returns :

the child at the specified index

Since 2.24


g_variant_get_fixed_array ()

gconstpointer       g_variant_get_fixed_array           (GVariant *value,
                                                         gsize *n_elements,
                                                         gsize element_size);

Provides access to the serialised data for an array of fixed-sized items.

value must be an array with fixed-sized elements. Numeric types are fixed-size as are tuples containing only other fixed-sized types.

element_size must be the size of a single element in the array. For example, if calling this function for an array of 32 bit integers, you might say sizeof (gint32). This value isn't used except for the purpose of a double-check that the form of the seralised data matches the caller's expectation.

n_elements, which must be non-NULL is set equal to the number of items in the array.

value :

a GVariant array with fixed-sized elements

n_elements :

a pointer to the location to store the number of items

element_size :

the size of each element

Returns :

a pointer to the fixed array

Since 2.24


g_variant_get_size ()

gsize               g_variant_get_size                  (GVariant *value);

Determines the number of bytes that would be required to store value with g_variant_store().

If value has a fixed-sized type then this function always returned that fixed size.

In the case that value is already in serialised form or the size has already been calculated (ie: this function has been called before) then this function is O(1). Otherwise, the size is calculated, an operation which is approximately O(n) in the number of values involved.

value :

a GVariant instance

Returns :

the serialised size of value

Since 2.24


g_variant_get_data ()

gconstpointer       g_variant_get_data                  (GVariant *value);

Returns a pointer to the serialised form of a GVariant instance. The returned data is in machine native byte order but may not be in fully-normalised form if read from an untrusted source. The returned data must not be freed; it remains valid for as long as value exists.

If value is a fixed-sized value that was deserialised from a corrupted serialised container then NULL may be returned. In this case, the proper thing to do is typically to use the appropriate number of nul bytes in place of value. If value is not fixed-sized then NULL is never returned.

In the case that value is already in serialised form, this function is O(1). If the value is not already in serialised form, serialisation occurs implicitly and is approximately O(n) in the size of the result.

value :

a GVariant instance

Returns :

the serialised form of value, or NULL

Since 2.24


g_variant_store ()

void                g_variant_store                     (GVariant *value,
                                                         gpointer data);

Stores the serialised form of value at data. data should be large enough. See g_variant_get_size().

The stored data is in machine native byte order but may not be in fully-normalised form if read from an untrusted source. See g_variant_normalise() for a solution.

This function is approximately O(n) in the size of data.

value :

the GVariant to store

data :

the location to store the serialised data at

Since 2.24


g_variant_hash ()

guint               g_variant_hash                      (gconstpointer value);

Generates a hash value for a GVariant instance.

The output of this function is guaranteed to be the same for a given value only per-process. It may change between different processor architectures or even different versions of GLib. Do not use this function as a basis for building protocols or file formats.

The type of value is gconstpointer only to allow use of this function with GHashTable. value must be a GVariant.

value :

a basic GVariant value as a gconstpointer

Returns :

a hash value corresponding to value

Since 2.24


g_variant_equal ()

gboolean            g_variant_equal                     (gconstpointer one,
                                                         gconstpointer two);

Checks if one and two have the same type and value.

The types of one and two are gconstpointer only to allow use of this function with GHashTable. They must each be a GVariant.

one :

a GVariant instance

two :

a GVariant instance

Returns :

TRUE if one and two are equal

Since 2.24


g_variant_print ()

gchar *             g_variant_print                     (GVariant *value,
                                                         gboolean type_annotate);

Pretty-prints value in the format understood by g_variant_parse().

If type_annotate is TRUE, then type information is included in the output.

value :

a GVariant

type_annotate :

TRUE if type information should be included in the output

Returns :

a newly-allocated string holding the result.

g_variant_print_string ()

GString *           g_variant_print_string              (GVariant *value,
                                                         GString *string,
                                                         gboolean type_annotate);

Behaves as g_variant_print(), but operates on a GString.

If string is non-NULL then it is appended to and returned. Else, a new empty GString is allocated and it is returned.

value :

a GVariant

string :

a GString, or NULL

type_annotate :

TRUE if type information should be included in the output

Returns :

a GString containing the string

Since 2.24

See Also

GVariantType