<GVariant>

<GVariant>

Description

GVariant is a variant datatype; it can contain one or more values along with information about the type of the values.

A GVariant may contain simple types, like an integer, or a boolean value; or complex types, like an array of two strings, or a dictionary of key value pairs. A GVariant is also immutable: once it's been created neither its type nor its content can be modified further.

GVariant is useful whenever data needs to be serialized, for example when sending method parameters in DBus, or when saving settings using GSettings.

When creating a new GVariant, you pass the data you want to store in it along with a string representing the type of data you wish to pass to it.

For instance, if you want to create a GVariant holding an integer value you can use:

  GVariant *v = g_variant_new ("u", 40);

The string "u" in the first argument tells GVariant that the data passed to the constructor (40) is going to be an unsigned integer.

More advanced examples of GVariant in use can be found in documentation for [GVariant format strings][gvariant-format-strings-pointers].

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 cannot 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 D-Bus. Almost all types of GVariant instances can be sent over D-Bus. See GVariantType for exceptions. (However, GVariant's serialisation format is not the same as the serialisation format of a D-Bus message body: use GDBusMessage, in the gio library, for those.)

For space-efficiency, the GVariant serialisation format does not automatically include the variant's length, type or endianness, which must either be implied from context (such as knowledge that a particular file format always contains a little-endian G_VARIANT_TYPE_VARIANT which occupies the whole length of the file) or supplied out-of-band (for instance, a length, type and/or endianness indicator could be placed at the beginning of a file, network message or network stream).

A GVariant's size is limited mainly by any lower level operating system constraints, such as the number of bits in gsize. For example, it is reasonable to have a 2GB file mapped into memory with GMappedFile, and call g_variant_new_from_data() on it.

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, not counting any indicator of the endianness, or of the length or type of the top-level variant.

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 32-bit 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 32-bit 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 look up 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 32-bit 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 referring 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 bytes 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.

Functions

byteswap

(define-values (%return) (variant:byteswap self))

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.

Parameters

value

a GVariant

Passed as self

check-format-string?

(define-values
  (%return)
  (variant:check-format-string? self format-string copy-only))

Checks if calling g_variant_get() with format_string on value would be valid from a type-compatibility standpoint. format_string is assumed to be a valid format string (from a syntactic standpoint).

If copy_only is TRUE then this function additionally checks that it would be safe to call g_variant_unref() on value immediately after the call to g_variant_get() without invalidating the result. This is only possible if deep copies are made (ie: there are no pointers to the data inside of the soon-to-be-freed GVariant instance). If this check fails then a g_critical() is printed and FALSE is returned.

This function is meant to be used by functions that wish to provide varargs accessors to GVariant values of uncertain values (eg: g_variant_lookup() or g_menu_model_get_item_attribute()).

Parameters

value

a GVariant

Passed as self

format_string

a valid GVariant format string

Passed as format-string

copy_only

TRUE to ensure the format string makes deep copies

Passed as copy-only

classify

(define-values (%return) (variant:classify self))

Classifies value according to its top-level type.

Parameters

value

a GVariant

Passed as self

compare

(define-values (%return) (variant:compare self two))

Compares one and two.

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

Comparison is only defined for basic types (ie: booleans, numbers, strings). For booleans, FALSE is less than TRUE. Numbers are ordered in the usual way. Strings are in ASCII lexographical order.

It is a programmer error to attempt to compare container values or two values that have types that are not exactly equal. For example, you cannot compare a 32-bit signed integer with a 32-bit unsigned integer. Also note that this function is not particularly well-behaved when it comes to comparison of doubles; in particular, the handling of incomparable values (ie: NaN) is undefined.

If you only require an equality comparison, g_variant_equal() is more general.

Parameters

one

a basic-typed GVariant instance

Passed as self

two

a GVariant instance of the same type

Passed as two

dup-bytestring

(define-values (%return length) (variant:dup-bytestring self))

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

The return value must be freed using g_free().

Parameters

value

an array-of-bytes GVariant instance

Passed as self

length

a pointer to a gsize, to store the length (not including the nul terminator)

Inferred from %return

dup-bytestring-array

(define-values (%return length) (variant:dup-bytestring-array self))

Gets the contents of an array of array of bytes 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.

Parameters

value

an array of array of bytes GVariant ('aay')

Passed as self

length

the length of the result, or NULL

Inferred from %return

dup-objv

(define-values (%return length) (variant:dup-objv self))

Gets the contents of an array of object paths 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.

Parameters

value

an array of object paths GVariant

Passed as self

length

the length of the result, or NULL

Inferred from %return

dup-string

(define-values (%return length) (variant:dup-string self))

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

The string will always be UTF-8 encoded.

The return value must be freed using g_free().

Parameters

value

a string GVariant instance

Passed as self

length

a pointer to a gsize, to store the length

Passed as length

dup-strv

(define-values (%return length) (variant:dup-strv self))

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.

Parameters

value

an array of strings GVariant

Passed as self

length

the length of the result, or NULL

Inferred from %return

equal?

(define-values (%return) (variant:equal? self 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.

Parameters

one

a GVariant instance

Passed as self

two

a GVariant instance

Passed as two

get-boolean?

(define-values (%return) (variant:get-boolean? self))

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.

Parameters

value

a boolean GVariant instance

Passed as self

get-byte

(define-values (%return) (variant:get-byte self))

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.

Parameters

value

a byte GVariant instance

Passed as self

get-bytestring

(define-values (%return) (variant:get-bytestring self))

Returns the string value of a GVariant instance with an array-of-bytes type. The string has no particular encoding.

If the array does not end with a nul terminator character, the empty string is returned. For this reason, you can always trust that a non-NULL nul-terminated string will be returned by this function.

If the array contains a nul terminator character somewhere other than the last byte then the returned string is the string, up to the first such nul character.

g_variant_get_fixed_array() should be used instead if the array contains arbitrary data that could not be nul-terminated or could contain nul bytes.

It is an error to call this function with a value that is not an array of bytes.

The return value remains valid as long as value exists.

Parameters

value

an array-of-bytes GVariant instance

Passed as self

get-bytestring-array

(define-values (%return length) (variant:get-bytestring-array self))

Gets the contents of an array of array of bytes 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.

Parameters

value

an array of array of bytes GVariant ('aay')

Passed as self

length

the length of the result, or NULL

Inferred from %return

get-child-value

(define-values (%return) (variant:get-child-value self 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().

The returned value is never floating. You should free it with g_variant_unref() when you're done with it.

Note that values borrowed from the returned child are not guaranteed to still be valid after the child is freed even if you still hold a reference to value, if value has not been serialised at the time this function is called. To avoid this, you can serialize value by calling g_variant_get_data() and optionally ignoring the return value.

There may be implementation specific restrictions on deeply nested values, which would result in the unit tuple being returned as the child value, instead of further nested children. GVariant is guaranteed to handle nesting up to at least 64 levels.

This function is O(1).

Parameters

value

a container GVariant

Passed as self

index_

the index of the child to fetch

Passed as index-

get-data

(define-values (%return) (variant:get-data self))

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.

To deserialise the data returned by this function, in addition to the serialised data, you must know the type of the GVariant, and (if the machine might be different) the endianness of the machine that stored it. As a result, file formats or network messages that incorporate serialised GVariants must include this information either implicitly (for instance "the file always contains a G_VARIANT_TYPE_VARIANT and it is always in little-endian order") or explicitly (by storing the type and/or endianness in addition to the serialised data).

Parameters

value

a GVariant instance

Passed as self

get-data-as-bytes

(define-values (%return) (variant:get-data-as-bytes self))

Returns a pointer to the serialised form of a GVariant instance. The semantics of this function are exactly the same as g_variant_get_data(), except that the returned GBytes holds a reference to the variant data.

Parameters

value

a GVariant

Passed as self

get-double

(define-values (%return) (variant:get-double self))

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.

Parameters

value

a double GVariant instance

Passed as self

get-handle

(define-values (%return) (variant:get-handle self))

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 D-Bus message. If you're not interacting with D-Bus, you probably don't need them.

Parameters

value

a handle GVariant instance

Passed as self

get-int16

(define-values (%return) (variant:get-int16 self))

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.

Parameters

value

an int16 GVariant instance

Passed as self

get-int32

(define-values (%return) (variant:get-int32 self))

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.

Parameters

value

an int32 GVariant instance

Passed as self

get-int64

(define-values (%return) (variant:get-int64 self))

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.

Parameters

value

an int64 GVariant instance

Passed as self

get-maybe

(define-values (%return) (variant:get-maybe self))

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

Parameters

value

a maybe-typed value

Passed as self

get-normal-form

(define-values (%return) (variant:get-normal-form self))

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.

If value is already in normal form, a new reference will be returned (which will be floating if value is floating). If it is not in normal form, the newly created GVariant will be returned with a single non-floating reference. Typically, g_variant_take_ref() should be called on the return value from this function to guarantee ownership of a single non-floating reference to it.

Parameters

value

a GVariant

Passed as self

get-objv

(define-values (%return length) (variant:get-objv self))

Gets the contents of an array of object paths 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.

Parameters

value

an array of object paths GVariant

Passed as self

length

the length of the result, or NULL

Inferred from %return

get-size

(define-values (%return) (variant:get-size self))

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.

Parameters

value

a GVariant instance

Passed as self

get-string

(define-values (%return length) (variant:get-string self))

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.

The string will always be UTF-8 encoded, will never be NULL, and will never contain nul bytes.

If length is non-NULL then the length of the string (in bytes) is returned there. For trusted values, this information is already known. Untrusted values will be validated and, if valid, a strlen() will be performed. If invalid, a default value will be returned — for G_VARIANT_TYPE_OBJECT_PATH, this is "/", and for other types it is the empty string.

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.

Parameters

value

a string GVariant instance

Passed as self

length

a pointer to a gsize, to store the length

Passed as length

get-strv

(define-values (%return length) (variant:get-strv self))

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.

Parameters

value

an array of strings GVariant

Passed as self

length

the length of the result, or NULL

Inferred from %return

get-type

(define-values (%return) (variant:get-type self))

Determines the type of value.

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

Parameters

value

a GVariant

Passed as self

get-type-string

(define-values (%return) (variant:get-type-string self))

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.

Parameters

value

a GVariant

Passed as self

get-uint16

(define-values (%return) (variant:get-uint16 self))

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.

Parameters

value

a uint16 GVariant instance

Passed as self

get-uint32

(define-values (%return) (variant:get-uint32 self))

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.

Parameters

value

a uint32 GVariant instance

Passed as self

get-uint64

(define-values (%return) (variant:get-uint64 self))

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.

Parameters

value

a uint64 GVariant instance

Passed as self

get-variant

(define-values (%return) (variant:get-variant self))

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

Parameters

value

a variant GVariant instance

Passed as self

hash

(define-values (%return) (variant:hash self))

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.

Parameters

value

a basic GVariant value as a gconstpointer

Passed as self

is-container?

(define-values (%return) (variant:is-container? self))

Checks if value is a container.

Parameters

value

a GVariant instance

Passed as self

is-floating?

(define-values (%return) (variant:is-floating? self))

Checks whether value has a floating reference count.

This function should only ever be used to assert that a given variant is or is not floating, or for debug purposes. To acquire a reference to a variant that might be floating, always use g_variant_ref_sink() or g_variant_take_ref().

See g_variant_ref_sink() for more information about floating reference counts.

Parameters

value

a GVariant

Passed as self

is-normal-form?

(define-values (%return) (variant:is-normal-form? self))

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_new_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.

There may be implementation specific restrictions on deeply nested values. GVariant is guaranteed to handle nesting up to at least 64 levels.

Parameters

value

a GVariant instance

Passed as self

is-of-type?

(define-values (%return) (variant:is-of-type? self type))

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

Parameters

value

a GVariant instance

Passed as self

type

a GVariantType

Passed as type

lookup-value

(define-values (%return) (variant:lookup-value self key expected-type))

Looks up a value in a dictionary GVariant.

This function works with dictionaries of the type a{s*} (and equally well with type a{o*}, but we only further discuss the string case for sake of clarity).

In the event that dictionary has the type a{sv}, the expected_type string specifies what type of value is expected to be inside of the variant. If the value inside the variant has a different type then NULL is returned. In the event that dictionary has a value type other than v then expected_type must directly match the value type and it is used to unpack the value directly or an error occurs.

In either case, if key is not found in dictionary, NULL is returned.

If the key is found and the value has the correct type, it is returned. If expected_type was specified then any non-NULL return value will have this type.

This function is currently implemented with a linear scan. If you plan to do many lookups then GVariantDict may be more efficient.

Parameters

dictionary

a dictionary GVariant

Passed as self

key

the key to look up in the dictionary

Passed as key

expected_type

a GVariantType, or NULL

Passed as expected-type

n-children

(define-values (%return) (variant:n-children self))

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).

Parameters

value

a container GVariant

Passed as self

print

(define-values (%return) (variant:print self type-annotate))

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

The format is described [here][gvariant-text].

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

Parameters

value

a GVariant

Passed as self

type_annotate

TRUE if type information should be included in the output

Passed as type-annotate

ref

(define-values (%return) (variant:ref self))

Increases the reference count of value.

Parameters

value

a GVariant

Passed as self

ref-sink

(define-values (%return) (variant:ref-sink self))

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.

Parameters

value

a GVariant

Passed as self

store

(define-values () (variant:store self 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_get_normal_form() for a solution.

As with g_variant_get_data(), to be able to deserialise the serialised variant successfully, its type and (if the destination machine might be different) its endianness must also be available.

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

Parameters

value

the GVariant to store

Passed as self

data

the location to store the serialised data at

Passed as data

take-ref

(define-values (%return) (variant:take-ref self))

If value is floating, sink it. Otherwise, do nothing.

Typically you want to use g_variant_ref_sink() in order to automatically do the correct thing with respect to floating or non-floating references, but there is one specific scenario where this function is helpful.

The situation where this function is helpful is when creating an API that allows the user to provide a callback function that returns a GVariant. We certainly want to allow the user the flexibility to return a non-floating reference from this callback (for the case where the value that is being returned already exists).

At the same time, the style of the GVariant API makes it likely that for newly-created GVariant instances, the user can be saved some typing if they are allowed to return a GVariant with a floating reference.

Using this function on the return value of the user's callback allows the user to do whichever is more convenient for them. The caller will always receives exactly one full reference to the value: either the one that was returned in the first place, or a floating reference that has been converted to a full reference.

This function has an odd interaction when combined with g_variant_ref_sink() running at the same time in another thread on the same GVariant instance. If g_variant_ref_sink() runs first then the result will be that the floating reference is converted to a hard reference. If g_variant_take_ref() runs first then the result will be that the floating reference is converted to a hard reference and an additional reference on top of that one is added. It is best to avoid this situation.

Parameters

value

a GVariant

Passed as self

unref

(define-values () (variant:unref self))

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

Parameters

value

a GVariant

Passed as self

variant:new-variant

(define-values (%return) (variant:new-variant value))

Undocumented

Parameters

value

Passed as value

variant:new-uint64

(define-values (%return) (variant:new-uint64 value))

Undocumented

Parameters

value

Passed as value

variant:new-uint32

(define-values (%return) (variant:new-uint32 value))

Undocumented

Parameters

value

Passed as value

variant:new-uint16

(define-values (%return) (variant:new-uint16 value))

Undocumented

Parameters

value

Passed as value

variant:new-tuple

(define-values (%return) (variant:new-tuple children))

Undocumented

Parameters

children

Passed as children

n_children

Inferred from children

variant:new-strv

(define-values (%return) (variant:new-strv strv))

Undocumented

Parameters

strv

Passed as strv

length

Inferred from strv

variant:new-string

(define-values (%return) (variant:new-string string))

Undocumented

Parameters

string

Passed as string

variant:new-signature

(define-values (%return) (variant:new-signature signature))

Undocumented

Parameters

signature

Passed as signature

variant:new-objv

(define-values (%return) (variant:new-objv strv))

Undocumented

Parameters

strv

Passed as strv

length

Inferred from strv

variant:new-object-path

(define-values (%return) (variant:new-object-path object-path))

Undocumented

Parameters

object_path

Passed as object-path

variant:new-maybe

(define-values (%return) (variant:new-maybe child-type child))

Undocumented

Parameters

child_type

Passed as child-type

child

Passed as child

variant:new-int64

(define-values (%return) (variant:new-int64 value))

Undocumented

Parameters

value

Passed as value

variant:new-int32

(define-values (%return) (variant:new-int32 value))

Undocumented

Parameters

value

Passed as value

variant:new-int16

(define-values (%return) (variant:new-int16 value))

Undocumented

Parameters

value

Passed as value

variant:new-handle

(define-values (%return) (variant:new-handle value))

Undocumented

Parameters

value

Passed as value

variant:new-from-data

(define-values
  (%return)
  (variant:new-from-data type data trusted notify user-data))

Undocumented

Parameters

type

Passed as type

data

Passed as data

size

Inferred from data

trusted

Passed as trusted

notify

Passed as notify

user_data

Passed as user-data

variant:new-from-bytes

(define-values (%return) (variant:new-from-bytes type bytes trusted))

Undocumented

Parameters

type

Passed as type

bytes

Passed as bytes

trusted

Passed as trusted

variant:new-fixed-array

(define-values
  (%return)
  (variant:new-fixed-array element-type elements n-elements element-size))

Undocumented

Parameters

element_type

Passed as element-type

elements

Passed as elements

n_elements

Passed as n-elements

element_size

Passed as element-size

variant:new-double

(define-values (%return) (variant:new-double value))

Undocumented

Parameters

value

Passed as value

variant:new-dict-entry

(define-values (%return) (variant:new-dict-entry key value))

Undocumented

Parameters

key

Passed as key

value

Passed as value

variant:new-bytestring-array

(define-values (%return) (variant:new-bytestring-array strv))

Undocumented

Parameters

strv

Passed as strv

length

Inferred from strv

variant:new-bytestring

(define-values (%return) (variant:new-bytestring string))

Undocumented

Parameters

string

Passed as string

variant:new-byte

(define-values (%return) (variant:new-byte value))

Undocumented

Parameters

value

Passed as value

variant:new-boolean

(define-values (%return) (variant:new-boolean value))

Undocumented

Parameters

value

Passed as value

variant:new-array

(define-values (%return) (variant:new-array child-type children))

Undocumented

Parameters

child_type

Passed as child-type

children

Passed as children

n_children

Inferred from children

variant:is-object-path?

(define-values (%return) (variant:is-object-path? string))

Determines if a given string is a valid D-Bus object path. You should ensure that a string is a valid D-Bus 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.

Parameters

string

a normal C nul-terminated string

Passed as string

variant:is-signature?

(define-values (%return) (variant:is-signature? string))

Determines if a given string is a valid D-Bus type signature. You should ensure that a string is a valid D-Bus type signature before passing it to g_variant_new_signature().

D-Bus type signatures consist of zero or more definite GVariantType strings in sequence.

Parameters

string

a normal C nul-terminated string

Passed as string

variant:parse

(define-values (%return) (variant:parse type text limit endptr))

Parses a GVariant from a text representation.

A single GVariant is parsed from the content of text.

The format is described [here][gvariant-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. It is never floating, and must be freed with g_variant_unref().

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

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

There may be implementation specific restrictions on deeply nested values, which would result in a G_VARIANT_PARSE_ERROR_RECURSION error. GVariant is guaranteed to handle nesting up to at least 64 levels.

Parameters

type

a GVariantType, or NULL

Passed as type

text

a string containing a GVariant in text form

Passed as text

limit

a pointer to the end of text, or NULL

Passed as limit

endptr

a location to store the end pointer, or NULL

Passed as endptr

variant:parse-error-print-context

(define-values (%return) (variant:parse-error-print-context error source-str))

Pretty-prints a message showing the context of a GVariant parse error within the string for which parsing was attempted.

The resulting string is suitable for output to the console or other monospace media where newlines are treated in the usual way.

The message will typically look something like one of the following:

unterminated string constant:
  (1, 2, 3, 'abc
            ^^^^

or

unable to find a common type:
  [1, 2, 3, 'str']
   ^        ^^^^^

The format of the message may change in a future version.

error must have come from a failed attempt to g_variant_parse() and source_str must be exactly the same string that caused the error. If source_str was not nul-terminated when you passed it to g_variant_parse() then you must add nul termination before using this function.

Parameters

error

a GError from the GVariantParseError domain

Passed as error

source_str

the string that was given to the parser

Passed as source-str

variant:parse-error-quark

(define-values (%return) (variant:parse-error-quark))

Undocumented

variant:parser-get-error-quark

(define-values (%return) (variant:parser-get-error-quark))

Same as g_variant_error_quark().