Variant

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 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 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) or supplied out-of-band (for instance, a 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.

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 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 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.

class Variant {

protected

GVariant* gVariant;

GVariant* getVariantStruct();

void* getStruct();

this(GVariant* gVariant);

this(bool boolean);

static Variant fromObjectPath(string path);

static Variant fromSignature(string signature);

static Variant fromByteString(string byteString);

static Variant fromObjv(string[] strv);

static Variant fromByteStringArray(string[] strv);

VariantType getType();

string getTypeString();

int isOfType(VariantType type);

int isContainer();

static int compare(void* one, void* two);

GVariantClass classify();

int checkFormatString(string formatString, int copyOnly);

void getVa(string formatString, string endptr, void** app);

this(string formatString, string endptr, void** app);

static int isObjectPath(string string);

static int isSignature(string string);

ushort getUint16();

double getDouble();

string getString(gsize length);

string dupString();

Variant getVariant();

string[] getStrv();

string[] dupStrv();

string[] getObjv();

string[] dupObjv();

string getBytestring();

string dupBytestring();

string[] getBytestringArray();

string[] dupBytestringArray();

this(VariantType childType, Variant child);

this(VariantType childType, Variant[] children);

this(Variant[] children);

this(Variant key, Variant value);

this(VariantType elementType, void[] elements, gsize elementSize);

Variant getMaybe();

gsize nChildren();

Variant getChildValue(gsize index);

Variant lookupValue(string key, VariantType expectedType);

void* getFixedArray(gsize* nElements, gsize elementSize);

gsize getSize();

void* getData();

Bytes getDataAsBytes();

void store(void* data);

this(VariantType type, void* data, gsize size, int trusted, GDestroyNotify notify, void* userData);

this(VariantType type, Bytes bytes, int trusted);

Variant byteswap();

Variant getNormalForm();

int isNormalForm();

static uint hash(void* value);

static int equal(void* one, void* two);

string print(int typeAnnotate);

StringG printString(StringG string, int typeAnnotate);

static Variant parse(VariantType type, string text, string limit, string endptr);

this(string format, void** app);

}

Constructors

this this(GVariant* gVariant): Sets our main struct and passes it to the parent class
this this(bool boolean): Creates a new boolean GVariant instance -- either TRUE or FALSE. Since 2.24
this
this(string formatString, string endptr, void** 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
this this(char value): Creates a new byte GVariant instance. Since 2.24
this this(short value): Creates a new int16 GVariant instance. Since 2.24
this this(ushort value): Creates a new uint16 GVariant instance. Since 2.24
this this(int value): Creates a new int32 GVariant instance. Since 2.24
this this(uint value): Creates a new uint32 GVariant instance. Since 2.24
this this(long value): Creates a new int64 GVariant instance. Since 2.24
this this(ulong value): Creates a new uint64 GVariant instance. Since 2.24
this this(double value): Creates a new double GVariant instance. Since 2.24
this this(string string): Creates a string GVariant with the contents of string. string must be valid utf8. Since 2.24
this this(Variant value): Boxes value. The result is a GVariant instance representing a variant containing the original value. If child is a floating reference (see g_variant_ref_sink()), the new instance takes ownership of child. Since 2.24
this this(string[] strv): Constructs an array of strings GVariant from the given array of strings. If length is -1 then strv is NULL-terminated. Since 2.24
this this(VariantType childType, Variant child): Depending on if child is NULL, either wraps child inside of a maybe container or creates a Nothing instance for the given type. At least one of child_type and child must be non-NULL. If child_type is non-NULL then it must be a definite type. If they are both non-NULL then child_type must be the type of child. If child is a floating reference (see g_variant_ref_sink()), the new instance takes ownership of child. Since 2.24
this this(VariantType childType, Variant[] 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. If the children are floating references (see g_variant_ref_sink()), the new instance takes ownership of them as if via g_variant_ref_sink(). Since 2.24
this this(Variant[] 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. If the children are floating references (see g_variant_ref_sink()), the new instance takes ownership of them as if via g_variant_ref_sink(). Since 2.24
this this(Variant key, Variant 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). If the key or value are floating references (see g_variant_ref_sink()), the new instance takes ownership of them as if via g_variant_ref_sink(). Since 2.24
this this(VariantType elementType, void[] elements, gsize elementSize): 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 serialised 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 2.32
this this(VariantType type, void* data, gsize size, int trusted, GDestroyNotify notify, void* userData): 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. If data was not stored in this machine's native endianness, any multi-byte numeric values in the returned variant will also be in non-native endianness. g_variant_byteswap() can be used to recover the original values. 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
this this(VariantType type, Bytes bytes, int trusted): Constructs a new serialised-mode GVariant instance. This is the inner interface for creation of new serialised values that gets called from various functions in gvariant.c. A reference is taken on bytes. Since 2.36
this
this(string format, void** 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.

Members

Functions

byteswap Variant byteswap(): 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
checkFormatString int checkFormatString(string formatString, int copyOnly): 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 Since 2.34
classify GVariantClass classify(): Classifies value according to its top-level type. Since 2.24
doref Variant doref(): Increases the reference count of value. Since 2.24
dupBytestring string dupBytestring(): 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(). Since 2.26
dupBytestringArray string[] dupBytestringArray(): 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. Since 2.26
dupObjv string[] dupObjv(): 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. Since 2.30
dupString string dupString(): Similar to g_variant_get_string() except that instead of returning a constant string, the string is duplicated. The string will always be utf8 encoded. The return value must be freed using g_free(). Since 2.24
dupStrv string[] dupStrv(): 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
getBoolean int getBoolean(): 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
getByte char getByte(): 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
getBytestring string getBytestring(): 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. 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. Since 2.26
getBytestringArray string[] getBytestringArray(): 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. Since 2.26
getChildValue Variant getChildValue(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(). The returned value is never floating. You should free it with g_variant_unref() when you're done with it. This function is O(1). Since 2.24
getData void* getData(): 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). Since 2.24
getDataAsBytes Bytes getDataAsBytes(): 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. Since 2.36
getDouble double getDouble(): 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
getFixedArray void* getFixedArray(gsize* nElements, gsize elementSize): 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, as given by the section on Serialised Data Memory. In particular, arrays of these fixed-sized types can be interpreted as an array of the given C type, with element_size set to Since 2.24
getHandle int getHandle(): 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. Since 2.24
getInt16 short getInt16(): 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
getInt32 int getInt32(): 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
getInt64 long getInt64(): 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
getMaybe Variant getMaybe(): Given a maybe-typed GVariant instance, extract its value. If the value is Nothing, then this function returns NULL. Since 2.24
getNormalForm Variant getNormalForm(): 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
getObjv string[] getObjv(): 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. Since 2.30
getSize gsize getSize(): 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
getString string getString(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. The string will always be utf8 encoded. 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
getStruct void* getStruct(): the main Gtk struct as a void*
getStrv string[] getStrv(): 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
getType VariantType getType(): Determines the type of value. The return value is valid for the lifetime of value and must not be freed. Since 2.24
getTypeString string getTypeString(): 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
getUint16 ushort getUint16(): 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
getUint32 uint getUint32(): 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
getUint64 ulong getUint64(): 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
getVa
void getVa(string formatString, string endptr, void** 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. format_string determines the C types that are used for unpacking the values and also determines if the values are copied or borrowed, see the section on GVariant Format Strings. Since 2.24
getVariant Variant getVariant(): Unboxes value. The result is the GVariant instance that was contained in value. Since 2.24
getVariantStruct GVariant* getVariantStruct(): Get the main Gtk struct
isContainer int isContainer(): Checks if value is a container. Since 2.24
isFloating int isFloating(): 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. Since 2.26
isNormalForm int isNormalForm(): 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. Since 2.24
isOfType int isOfType(VariantType type): Checks if a value has a type matching the provided type. Since 2.24
lookupValue Variant lookupValue(string key, VariantType expectedType): 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 key 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. Since 2.28
nChildren gsize nChildren(): 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
print string print(int typeAnnotate): Pretty-prints value in the format understood by g_variant_parse(). The format is described here. If type_annotate is TRUE, then type information is included in the output. Since 2.24
printString StringG printString(StringG string, int typeAnnotate): 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
refSink Variant refSink(): 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
store void store(void* 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. Since 2.24
takeRef Variant takeRef(): 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 alway 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.
unref void unref(): Decreases the reference count of value. When its reference count drops to 0, the memory used by the variant is freed. Since 2.24

Static functions

compare int compare(void* one, void* 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. Since 2.26
equal int equal(void* one, void* 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
fromByteString Variant fromByteString(string byteString): Creates an array-of-bytes GVariant with the contents of string. This function is just like new Variant(string) except that the string need not be valid utf8.
fromByteStringArray Variant fromByteStringArray(string[] strv): Constructs an array of bytestring GVariant from the given array of strings. If length is -1 then strv is NULL-terminated. Since 2.26
fromObjectPath Variant fromObjectPath(string path): Creates a DBus object path GVariant with the contents of string. string must be a valid DBus object path. Use Variant.isObjectPath() if you're not sure. Since 2.24
fromObjv Variant fromObjv(string[] strv): Constructs an array of object paths Variant from the given array of strings.
fromSignature Variant fromSignature(string signature): Creates a DBus type signature GVariant with the contents of string. string must be a valid DBus type signature. Use Variant.isSignature() if you're not sure. Since 2.24
hash uint hash(void* 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
isObjectPath int isObjectPath(string 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. Since 2.24
isSignature int isSignature(string 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. Since 2.24
parse Variant parse(VariantType type, string text, string limit, string endptr): Parses a GVariant from a text representation. A single GVariant is parsed from the content of text. The format is described here. 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 occurred. Officially, the language understood by the parser is "any string produced by g_variant_print()".

Variables

gVariant GVariant* gVariant;: the main Gtk struct