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.

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.

Since 2.24

g_variant_ref ()

GVariant *          g_variant_ref                       (GVariant *value);

Increases the reference count of 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.

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.

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.

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.

Since 2.24

g_variant_is_container ()

gboolean            g_variant_is_container              (GVariant *value);

Checks if value is a container.

g_variant_classify ()

GVariantClass       g_variant_classify                  (GVariant *value);

Classifies value according to its top-level type.

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.

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.

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.

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).

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.

Since 2.24

g_variant_new_boolean ()

GVariant *          g_variant_new_boolean               (gboolean boolean);

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

Since 2.24

g_variant_new_byte ()

GVariant *          g_variant_new_byte                  (guchar byte);

Creates 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.

Since 2.24

g_variant_new_uint16 ()

GVariant *          g_variant_new_uint16                (guint16 uint16);

Creates 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.

Since 2.24

g_variant_new_uint32 ()

GVariant *          g_variant_new_uint32                (guint32 uint32);

Creates 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.

Since 2.24

g_variant_new_uint64 ()

GVariant *          g_variant_new_uint64                (guint64 uint64);

Creates 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.

Since 2.24

g_variant_new_double ()

GVariant *          g_variant_new_double                (gdouble floating);

Creates 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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().

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.

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.

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.

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.

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.

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.

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).

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.

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).

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).

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().

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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().

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.

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.

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.

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.

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/* 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);
    }
}

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.

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/* 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().

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.

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/* 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().

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.

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.

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().

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.

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.

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.

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);
}

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.

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).

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).

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()".

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.

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:

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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 "%@".