## 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;

    void                g_variant_get                       (GVariant *value,
                                                             const gchar *format_string,
                                                             ...);
    void                g_variant_get_va                    (GVariant *value,
                                                             const gchar *format_string,
                                                             const gchar **endptr,
                                                             va_list *app);
    GVariant *          g_variant_new                       (const gchar *format_string,
                                                             ...);
    GVariant *          g_variant_new_va                    (const gchar *format_string,
                                                             const gchar **endptr,
                                                             va_list *app);

    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_);
    void                g_variant_get_child                 (GVariant *value,
                                                             gsize index_,
                                                             const gchar *format_string,
                                                             ...);
    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);
    GVariant *          g_variant_new_from_data             (const GVariantType *type,
                                                             gconstpointer data,
                                                             gsize size,
                                                             gboolean trusted,
                                                             GDestroyNotify notify,
                                                             gpointer user_data);
    GVariant *          g_variant_byteswap                  (GVariant *value);
    GVariant *          g_variant_get_normal_form           (GVariant *value);
    gboolean            g_variant_is_normal_form            (GVariant *value);

    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);

                        GVariantIter;
    GVariantIter *      g_variant_iter_copy                 (GVariantIter *iter);
    void                g_variant_iter_free                 (GVariantIter *iter);
    gsize               g_variant_iter_init                 (GVariantIter *iter,
                                                             GVariant *value);
    gsize               g_variant_iter_n_children           (GVariantIter *iter);
    GVariantIter *      g_variant_iter_new                  (GVariant *value);
    GVariant *          g_variant_iter_next_value           (GVariantIter *iter);
    gboolean            g_variant_iter_next                 (GVariantIter *iter,
                                                             const gchar *format_string,
                                                             ...);
    gboolean            g_variant_iter_loop                 (GVariantIter *iter,
                                                             const gchar *format_string,
                                                             ...);

                        GVariantBuilder;
    void                g_variant_builder_unref             (GVariantBuilder *builder);
    GVariantBuilder *   g_variant_builder_ref               (GVariantBuilder *builder);
    GVariantBuilder *   g_variant_builder_new               (const GVariantType *type);
    void                g_variant_builder_init              (GVariantBuilder *builder,
                                                             const GVariantType *type);
    void                g_variant_builder_clear             (GVariantBuilder *builder);
    void                g_variant_builder_add_value         (GVariantBuilder *builder,
                                                             GVariant *value);
    void                g_variant_builder_add               (GVariantBuilder *builder,
                                                             const gchar *format_string,
                                                             ...);
    GVariant *          g_variant_builder_end               (GVariantBuilder *builder);
    void                g_variant_builder_open              (GVariantBuilder *builder,
                                                             const GVariantType *type);
    void                g_variant_builder_close             (GVariantBuilder *builder);

    #define             G_VARIANT_PARSE_ERROR
    GVariant *          g_variant_parse                     (const GVariantType *type,
                                                             const gchar *text,
                                                             const gchar *limit,
                                                             const gchar **endptr,
                                                             GError **error);
    GVariant *          g_variant_new_parsed_va             (const gchar *format,
                                                             va_list *app);
    GVariant *          g_variant_new_parsed                (const gchar *format,
                                                             ...);

## 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_get ()

    void                g_variant_get                       (GVariant *value,
                                                             const gchar *format_string,
                                                             ...);

Deconstructs a GVariant instance.

Think of this function as an analogue to `scanf()`.

The arguments that are expected by this function are entirely determined by `format_string`. `format_string` also restricts the permissible types of `value`. It is an error to give a value with an incompatible type. See the section on GVariant Format Strings. Please note that the syntax of the format string is very likely to be extended in the future.

`value` : | a GVariant instance
`format_string` : | a GVariant format string
`...` : | arguments, as per `format_string`

Since 2.24

### g_variant_get_va ()

    void                g_variant_get_va                    (GVariant *value,
                                                             const gchar *format_string,
                                                             const gchar **endptr,
                                                             va_list *app);

This function is intended to be used by libraries based on GVariant that want to provide `g_variant_get()`-like functionality to their users.

The API is more general than `g_variant_get()` to allow a wider range of possible uses.

`format_string` must still point to a valid format string, but it only need to be nul-terminated if `endptr` is `NULL`. If `endptr` is non-`NULL` then it is updated to point to the first character past the end of the format string.

`app` is a pointer to a va_list. The arguments, according to `format_string`, are collected from this va_list and the list is left pointing to the argument following the last.

These two generalisations allow mixing of multiple calls to `g_variant_new_va()` and `g_variant_get_va()` within a single actual varargs call by the user.

`value` : | a GVariant
`format_string` : | a string that is prefixed with a format string
`endptr` : | location to store the end pointer, or `NULL`
`app` : | a pointer to a va_list

Since 2.24

### g_variant_new ()

    GVariant *          g_variant_new                       (const gchar *format_string,
                                                             ...);

Creates a new GVariant instance.

Think of this function as an analogue to `g_strdup_printf()`.

The type of the created instance and the arguments that are expected by this function are determined by `format_string`. See the section on GVariant Format Strings. Please note that the syntax of the format string is very likely to be extended in the future.

The first character of the format string must not be '*' '?' '@' or 'r'; in essence, a new GVariant must always be constructed by this function (and not merely passed through it unmodified).

`format_string` : | a GVariant format string
`...` : | arguments, as per `format_string`
Returns : | a new floating GVariant instance

Since 2.24

### g_variant_new_va ()

    GVariant *          g_variant_new_va                    (const gchar *format_string,
                                                             const gchar **endptr,
                                                             va_list *app);

This function is intended to be used by libraries based on GVariant that want to provide `g_variant_new()`-like functionality to their users.

The API is more general than `g_variant_new()` to allow a wider range of possible uses.

`format_string` must still point to a valid format string, but it only needs to be nul-terminated if `endptr` is `NULL`. If `endptr` is non-`NULL` then it is updated to point to the first character past the end of the format string.

`app` is a pointer to a va_list. The arguments, according to `format_string`, are collected from this va_list and the list is left pointing to the argument following the last.

These two generalisations allow mixing of multiple calls to `g_variant_new_va()` and `g_variant_get_va()` within a single actual varargs call by the user.

The return value will be floating if it was a newly created GVariant instance (for example, if the format string was "(ii)"). In the case that the format_string was '*', '?', 'r', or a format starting with '@' then the collected GVariant pointer will be returned unmodified, without adding any additional references.

In order to behave correctly in all cases it is necessary for the calling function to `g_variant_ref_sink()` the return result before returning control to the user that originally provided the pointer. At this point, the caller will have their own full reference to the result. This can also be done by adding the result to a container, or by passing it to another `g_variant_new()` call.

`format_string` : | a string that is prefixed with a format string
`endptr` : | location to store the end pointer, or `NULL`
`app` : | a pointer to a va_list
Returns : | a new, usually floating, GVariant

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_child ()

    void                g_variant_get_child                 (GVariant *value,
                                                             gsize index_,
                                                             const gchar *format_string,
                                                             ...);

Reads a child item out of a container GVariant instance and deconstructs it according to `format_string`. This call is essentially a combination of `g_variant_get_child_value()` and `g_variant_get()`.

`value` : | a container GVariant
`index_` : | the index of the child to deconstruct
`format_string` : | a GVariant format string
`...` : | arguments, as per `format_string`

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 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_new_from_data ()

    GVariant *          g_variant_new_from_data             (const GVariantType *type,
                                                             gconstpointer data,
                                                             gsize size,
                                                             gboolean trusted,
                                                             GDestroyNotify notify,
                                                             gpointer user_data);

Creates a new GVariant instance from serialised data.

`type` is the type of GVariant instance that will be constructed. The interpretation of `data` depends on knowing the type.

`data` is not modified by this function and must remain valid with an unchanging value until such a time as `notify` is called with `user_data`. If the contents of `data` change before that time then the result is undefined.

If `data` is trusted to be serialised data in normal form then `trusted` should be `TRUE`. This applies to serialised data created within this process or read from a trusted location on the disk (such as a file installed in /usr/lib alongside your application). You should set trusted to `FALSE` if `data` is read from the network, a file in the user's home directory, etc.

`notify` will be called with `user_data` when `data` is no longer needed. The exact time of this call is unspecified and might even be before this function returns.

`type` : | a GVariantType
`data` : | the serialised data
`size` : | the size of `data`
`trusted` : | `TRUE` if `data` is definitely in normal form
`notify` : | function to call when `data` is no longer needed
`user_data` : | data for `notify`
Returns : | a new floating GVariant of type `type`

Since 2.24

### g_variant_byteswap ()

    GVariant *          g_variant_byteswap                  (GVariant *value);

Performs a byteswapping operation on the contents of `value`. The result is that all multi-byte numeric data contained in `value` is byteswapped. That includes 16, 32, and 64bit signed and unsigned integers as well as file handles and double precision floating point values.

This function is an identity mapping on any value that does not contain multi-byte numeric data. That include strings, booleans, bytes and containers containing only these things (recursively).

The returned value is always in normal form and is marked as trusted.

`value` : | a GVariant
Returns : | the byteswapped form of `value`

Since 2.24

### g_variant_get_normal_form ()

    GVariant *          g_variant_get_normal_form           (GVariant *value);

Gets a GVariant instance that has the same value as `value` and is trusted to be in normal form.

If `value` is already trusted to be in normal form then a new reference to `value` is returned.

If `value` is not already trusted, then it is scanned to check if it is in normal form. If it is found to be in normal form then it is marked as trusted and a new reference to it is returned.

If `value` is found not to be in normal form then a new trusted GVariant is created with the same value as `value`.

It makes sense to call this function if you've received GVariant data from untrusted sources and you want to ensure your serialised output is definitely in normal form.

`value` : | a GVariant
Returns : | a trusted GVariant

Since 2.24

### g_variant_is_normal_form ()

    gboolean            g_variant_is_normal_form            (GVariant *value);

Checks if `value` is in normal form.

The main reason to do this is to detect if a given chunk of serialised data is in normal form: load the data into a GVariant using `g_variant_create_from_data()` and then use this function to check.

If `value` is found to be in normal form then it will be marked as being trusted. If the value was already marked as being trusted then this function will immediately return `TRUE`.

`value` : | a GVariant instance
Returns : | `TRUE` if `value` is in normal form

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

### GVariantIter

    typedef struct {
    } GVariantIter;

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

### g_variant_iter_copy ()

    GVariantIter *      g_variant_iter_copy                 (GVariantIter *iter);

Creates a new heap-allocated GVariantIter to iterate over the container that was being iterated over by `iter`. Iteration begins on the new iterator from the current position of the old iterator but the two copies are independent past that point.

Use `g_variant_iter_free()` to free the return value when you no longer need it.

A reference is taken to the container that `iter` is iterating over and will be releated only when `g_variant_iter_free()` is called.

`iter` : | a GVariantIter
Returns : | a new heap-allocated GVariantIter

Since 2.24

### g_variant_iter_free ()

    void                g_variant_iter_free                 (GVariantIter *iter);

Frees a heap-allocated GVariantIter. Only call this function on iterators that were returned by `g_variant_iter_new()` or `g_variant_iter_copy()`.

`iter` : | a heap-allocated GVariantIter

Since 2.24

### g_variant_iter_init ()

    gsize               g_variant_iter_init                 (GVariantIter *iter,
                                                             GVariant *value);

Initialises (without allocating) a GVariantIter. `iter` may be completely uninitialised prior to this call; its old value is ignored.

The iterator remains valid for as long as `value` exists, and need not be freed in any way.

`iter` : | a pointer to a GVariantIter
`value` : | a container GVariant
Returns : | the number of items in `value`

Since 2.24

### g_variant_iter_n_children ()

    gsize               g_variant_iter_n_children           (GVariantIter *iter);

Queries the number of child items in the container that we are iterating over. This is the total number of items -- not the number of items remaining.

This function might be useful for preallocation of arrays.

`iter` : | a GVariantIter
Returns : | the number of children in the container

Since 2.24

### g_variant_iter_new ()

    GVariantIter *      g_variant_iter_new                  (GVariant *value);

Creates a heap-allocated GVariantIter for iterating over the items in `value`.

Use `g_variant_iter_free()` to free the return value when you no longer need it.

A reference is taken to `value` and will be released only when `g_variant_iter_free()` is called.

`value` : | a container GVariant
Returns : | a new heap-allocated GVariantIter

Since 2.24

### g_variant_iter_next_value ()

    GVariant *          g_variant_iter_next_value           (GVariantIter *iter);

Gets the next item in the container. If no more items remain then `NULL` is returned.

Use `g_variant_unref()` to drop your reference on the return value when you no longer need it.

Example 23. Iterating with `g_variant_iter_next_value()`

      /* recursively iterate a container */
      void
      iterate_container_recursive (GVariant *container)
      {
        GVariantIter iter;
        GVariant *child;

        g_variant_iter_init (&iter, dictionary);
        while ((child = g_variant_iter_next_value (&iter)))
          {
            g_print ("type '%s'\n", g_variant_get_type_string (child));

            if (g_variant_is_container (child))
              iterate_container_recursive (child);

            g_variant_unref (child);
          }
      }

`iter` : | a GVariantIter
Returns : | a GVariant, or `NULL`

Since 2.24

### g_variant_iter_next ()

    gboolean            g_variant_iter_next                 (GVariantIter *iter,
                                                             const gchar *format_string,
                                                             ...);

Gets the next item in the container and unpacks it into the variable argument list according to `format_string`, returning `TRUE`.

If no more items remain then `FALSE` is returned.

All of the pointers given on the variable arguments list of this function are assumed to point at uninitialised memory. It is the responsibility of the caller to free all of the values returned by the unpacking process.

Example 24. Memory management with `g_variant_iter_next()`

      /* Iterates a dictionary of type 'a{sv}' */
      void
      iterate_dictionary (GVariant *dictionary)
      {
        GVariantIter iter;
        GVariant *value;
        gchar *key;

        g_variant_iter_init (&iter, dictionary);
        while (g_variant_iter_next (&iter, "{sv}", &key, &value))
          {
            g_print ("Item '%s' has type '%s'\n", key,
                     g_variant_get_type_string (value));

            /* must free data for ourselves */
            g_variant_unref (value);
            g_free (key);
          }
      }

For a solution that is likely to be more convenient to C programmers when dealing with loops, see `g_variant_iter_loop()`.

`iter` : | a GVariantIter
`format_string` : | a GVariant format string
`...` : | the arguments to unpack the value into
Returns : | `TRUE` if a value was unpacked, or `FALSE` if there as no value

Since 2.24

### g_variant_iter_loop ()

    gboolean            g_variant_iter_loop                 (GVariantIter *iter,
                                                             const gchar *format_string,
                                                             ...);

Gets the next item in the container and unpacks it into the variable argument list according to `format_string`, returning `TRUE`.

If no more items remain then `FALSE` is returned.

On the first call to this function, the pointers appearing on the variable argument list are assumed to point at uninitialised memory. On the second and later calls, it is assumed that the same pointers will be given and that they will point to the memory as set by the previous call to this function. This allows the previous values to be freed, as appropriate.

This function is intended to be used with a while loop as demonstrated in the following example. This function can only be used when iterating over an array. It is only valid to call this function with a string constant for the format string and the same string constant must be used each time. Mixing calls to this function and `g_variant_iter_next()` or `g_variant_iter_next_value()` on the same iterator is not recommended.

Example 25. Memory management with `g_variant_iter_loop()`

      /* Iterates a dictionary of type 'a{sv}' */
      void
      iterate_dictionary (GVariant *dictionary)
      {
        GVariantIter iter;
        GVariant *value;
        gchar *key;

        g_variant_iter_init (&iter, dictionary);
        while (g_variant_iter_loop (&iter, "{sv}", &key, &value))
          {
            g_print ("Item '%s' has type '%s'\n", key,
                     g_variant_get_type_string (value));

            /* no need to free 'key' and 'value' here */
          }
      }

If you want a slightly less magical alternative that requires more typing, see `g_variant_iter_next()`.

`iter` : | a GVariantIter
`format_string` : | a GVariant format string
`...` : | the arguments to unpack the value into
Returns : | `TRUE` if a value was unpacked, or `FALSE` if there as no value

Since 2.24

### GVariantBuilder

    typedef struct {
    } GVariantBuilder;

A utility type for constructing container-type GVariant instances.

This is an opaque structure and may only be accessed using the following functions.

GVariantBuilder is not threadsafe in any way. Do not attempt to access it from more than one thread.

### g_variant_builder_unref ()

    void                g_variant_builder_unref             (GVariantBuilder *builder);

Decreases the reference count on `builder`.

In the event that there are no more references, releases all memory associated with the GVariantBuilder.

Don't call this on stack-allocated GVariantBuilder instances or bad things will happen.

`builder` : | a GVariantBuilder allocated by `g_variant_builder_new()`

Since 2.24

### g_variant_builder_ref ()

    GVariantBuilder *   g_variant_builder_ref               (GVariantBuilder *builder);

Increases the reference count on `builder`.

Don't call this on stack-allocated GVariantBuilder instances or bad things will happen.

`builder` : | a GVariantBuilder allocated by `g_variant_builder_new()`
Returns : | a new reference to `builder`

Since 2.24

### g_variant_builder_new ()

    GVariantBuilder *   g_variant_builder_new               (const GVariantType *type);

Allocates and initialises a new GVariantBuilder.

You should call `g_variant_builder_unref()` on the return value when it is no longer needed. The memory will not be automatically freed by any other call.

In most cases it is easier to place a GVariantBuilder directly on the stack of the calling function and initialise it with `g_variant_builder_init()`.

`type` : | a container type
Returns : | a GVariantBuilder

Since 2.24

### g_variant_builder_init ()

    void                g_variant_builder_init              (GVariantBuilder *builder,
                                                             const GVariantType *type);

Initialises a GVariantBuilder structure.

`type` must be non-`NULL`. It specifies the type of container to construct. It can be an indefinite type such as `G_VARIANT_TYPE_ARRAY` or a definite type such as "as" or "(ii)". Maybe, array, tuple, dictionary entry and variant-typed values may be constructed.

After the builder is initialised, values are added using `g_variant_builder_add_value()` or `g_variant_builder_add()`.

After all the child values are added, `g_variant_builder_end()` frees the memory associated with the builder and returns the GVariant that was created.

This function completely ignores the previous contents of `builder`. On one hand this means that it is valid to pass in completely uninitialised memory. On the other hand, this means that if you are initialising over top of an existing GVariantBuilder you need to first call `g_variant_builder_clear()` in order to avoid leaking memory.

You must not call `g_variant_builder_ref()` or `g_variant_builder_unref()` on a GVariantBuilder that was initialised with this function. If you ever pass a reference to a GVariantBuilder outside of the control of your own code then you should assume that the person receiving that reference may try to use reference counting; you should use `g_variant_builder_new()` instead of this function.

`builder` : | a GVariantBuilder
`type` : | a container type

Since 2.24

### g_variant_builder_clear ()

    void                g_variant_builder_clear             (GVariantBuilder *builder);

Releases all memory associated with a GVariantBuilder without freeing the GVariantBuilder structure itself.

It typically only makes sense to do this on a stack-allocated GVariantBuilder if you want to abort building the value part-way through. This function need not be called if you call `g_variant_builder_end()` and it also doesn't need to be called on builders allocated with g_variant_builder_new (see `g_variant_builder_free()` for that).

This function leaves the GVariantBuilder structure set to all-zeros. It is valid to call this function on either an initialised GVariantBuilder or one that is set to all-zeros but it is not valid to call this function on uninitialised memory.

`builder` : | a GVariantBuilder

Since 2.24

### g_variant_builder_add_value ()

    void                g_variant_builder_add_value         (GVariantBuilder *builder,
                                                             GVariant *value);

Adds `value` to `builder`.

It is an error to call this function in any way that would create an inconsistent value to be constructed. Some examples of this are putting different types of items into an array, putting the wrong types or number of items in a tuple, putting more than one value into a variant, etc.

`builder` : | a GVariantBuilder
`value` : | a GVariant

Since 2.24

### g_variant_builder_add ()

    void                g_variant_builder_add               (GVariantBuilder *builder,
                                                             const gchar *format_string,
                                                             ...);

Adds to a GVariantBuilder.

This call is a convenience wrapper that is exactly equivalent to calling `g_variant_new()` followed by `g_variant_builder_add_value()`.

This function might be used as follows:

    GVariant *
    make_pointless_dictionary (void)
    {
      GVariantBuilder *builder;
      int i;

      builder = g_variant_builder_new (G_VARIANT_TYPE_CLASS_ARRAY,
                                       NULL);
      for (i = 0; i < 16; i++)
        {
          gchar buf[3];

          sprintf (buf, "%d", i);
          g_variant_builder_add (builder, "{is}", i, buf);
        }

      return g_variant_builder_end (builder);
    }

`builder` : | a GVariantBuilder
`format_string` : | a GVariant varargs format string
`...` : | arguments, as per `format_string`

Since 2.24

### g_variant_builder_end ()

    GVariant *          g_variant_builder_end               (GVariantBuilder *builder);

Ends the builder process and returns the constructed value.

This call automatically reduces the reference count on `builder` by one, unless it has previously had `g_variant_builder_no_autofree()` called on it. Unless you've taken other actions, this is usually sufficient to free `builder`.

Even if additional references are held, it is not permissible to use `builder` in any way after this call except for further reference counting operations.

It is an error to call this function in any way that would create an inconsistent value to be constructed (ie: insufficient number of items added to a container with a specific number of children required). It is also an error to call this function if the builder was created with an indefinite array or maybe type and no children have been added; in this case it is impossible to infer the type of the empty array.

`builder` : | a GVariantBuilder
Returns : | a new, floating, GVariant

Since 2.24

### g_variant_builder_open ()

    void                g_variant_builder_open              (GVariantBuilder *builder,
                                                             const GVariantType *type);

Opens a subcontainer inside the given `builder`. When done adding items to the subcontainer, `g_variant_builder_close()` must be called.

It is an error to call this function in any way that would cause an inconsistent value to be constructed (ie: adding too many values or a value of an incorrect type).

`builder` : | a GVariantBuilder
`type` : | a GVariantType

Since 2.24

### g_variant_builder_close ()

    void                g_variant_builder_close             (GVariantBuilder *builder);

Closes the subcontainer inside the given `builder` that was opened by the most recent call to `g_variant_builder_open()`.

It is an error to call this function in any way that would create an inconsistent value to be constructed (ie: too few values added to the subcontainer).

`builder` : | a GVariantBuilder

Since 2.24

### G_VARIANT_PARSE_ERROR

    #define G_VARIANT_PARSE_ERROR (g_variant_parser_get_error_quark ())

Error domain for GVariant text format parsing. Specific error codes are not currently defined for this domain. See GError for information on error domains.

### g_variant_parse ()

    GVariant *          g_variant_parse                     (const GVariantType *type,
                                                             const gchar *text,
                                                             const gchar *limit,
                                                             const gchar **endptr,
                                                             GError **error);

Parses a GVariant from a text representation.

A single GVariant is parsed from the content of `text`.

The memory at `limit` will never be accessed and the parser behaves as if the character at `limit` is the nul terminator. This has the effect of bounding `text`.

If `endptr` is non-`NULL` then `text` is permitted to contain data following the value that this function parses and `endptr` will be updated to point to the first character past the end of the text parsed by this function. If `endptr` is `NULL` and there is extra data then an error is returned.

If `type` is non-`NULL` then the value will be parsed to have that type. This may result in additional parse errors (in the case that the parsed value doesn't fit the type) but may also result in fewer errors (in the case that the type would have been ambiguous, such as with empty arrays).

In the event that the parsing is successful, the resulting GVariant is returned.

In case of any error, `NULL` will be returned. If `error` is non-`NULL` then it will be set to reflect the error that occured.

Officially, the language understood by the parser is "any string produced by `g_variant_print()`".

`type` : | a GVariantType, or `NULL`
`text` : | a string containing a GVariant in text form
`limit` : | a pointer to the end of `text`, or `NULL`
`endptr` : | a location to store the end pointer, or `NULL`
`error` : | a pointer to a `NULL` GError pointer, or `NULL`
Returns : | a reference to a GVariant, or `NULL`

### g_variant_new_parsed_va ()

    GVariant *          g_variant_new_parsed_va             (const gchar *format,
                                                             va_list *app);

Parses `format` and returns the result.

This is the version of `g_variant_new_parsed()` intended to be used from libraries.

The return value will be floating if it was a newly created GVariant instance. In the case that `format` simply specified the collection of a GVariant pointer (eg: `format` was "%*") then the collected GVariant pointer will be returned unmodified, without adding any additional references.

In order to behave correctly in all cases it is necessary for the calling function to `g_variant_ref_sink()` the return result before returning control to the user that originally provided the pointer. At this point, the caller will have their own full reference to the result. This can also be done by adding the result to a container, or by passing it to another `g_variant_new()` call.

`format` : | a text format GVariant
`app` : | a pointer to a va_list
Returns : | a new, usually floating, GVariant

### g_variant_new_parsed ()

    GVariant *          g_variant_new_parsed                (const gchar *format,
                                                             ...);

Parses `format` and returns the result.

`format` must be a text format GVariant with one extention: at any point that a value may appear in the text, a '%' character followed by a GVariant format string (as per `g_variant_new()`) may appear. In that case, the same arguments are collected from the argument list as `g_variant_new()` would have collected.

Consider this simple example:

     g_variant_new_parsed ("[('one', 1), ('two', %i), (%s, 3)]", 2, "three");

In the example, the variable argument parameters are collected and filled in as if they were part of the original string to produce the result of `[('one', 1), ('two', 2), ('three', 3)]`.

This function is intended only to be used with `format` as a string literal. Any parse error is fatal to the calling process. If you want to parse data from untrusted sources, use `g_variant_parse()`.

You may not use this function to return, unmodified, a single GVariant pointer from the argument list. ie: `format` may not solely be anything along the lines of "%*", "%?", "`r`", or anything starting with "%@".

`format` : | a text format GVariant
`...` : | arguments as per `format`
Returns : | a new floating GVariant instance

## See Also

GVariantType