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:
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.
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
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_is_floating ()
gboolean
g_variant_is_floating (GVariant *value);
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.
Returns
whether value
is floating
Since: 2.26
g_variant_take_ref ()
GVariant *
g_variant_take_ref (GVariant *value);
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.
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.
Returns
the type string for the type of value
Since: 2.24
g_variant_is_of_type ()
gboolean
g_variant_is_of_type (GVariant *value,
const GVariantType *type);
Checks if a value has a type matching the provided type.
Returns
TRUE if the type of value
matches type
Since: 2.24
g_variant_is_container ()
gboolean
g_variant_is_container (GVariant *value);
Checks if value
is a container.
Returns
TRUE if value
is a container
Since: 2.24
g_variant_compare ()
gint
g_variant_compare (gconstpointer one,
gconstpointer 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.
Returns
negative value if a < b;
zero if a = b;
positive value if a > b.
Since: 2.26
g_variant_classify ()
GVariantClass
g_variant_classify (GVariant *value);
Classifies value
according to its top-level type.
Since: 2.24
g_variant_check_format_string ()
gboolean
g_variant_check_format_string (GVariant *value,
const gchar *format_string,
gboolean 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()).
Returns
TRUE if format_string
is safe to use
Since: 2.34
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.
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.
[skip]
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.
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.
[skip]
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).
Note that the arguments must be of the correct width for their types
specified in format_string
. This can be achieved by casting them. See
the GVariant varargs documentation.
[skip]
Returns
a new floating GVariant instance
Since: 2.24
g_variant_new_va ()
GVariant *
g_variant_new_va (const gchar *format_string,
const gchar **endptr,
va_list *app);
This function is intended to be used by libraries based on
GVariant that want to provide g_variant_new()-like functionality
to their users.
The API is more general than g_variant_new() to allow a wider range
of possible uses.
format_string
must still point to a valid format string, but it only
needs to be nul-terminated if endptr
is NULL. If endptr
is
non-NULL then it is updated to point to the first character past the
end of the format string.
app
is a pointer to a va_list. The arguments, according to
format_string
, are collected from this va_list and the list is left
pointing to the argument following the last.
Note that the arguments in app
must be of the correct width for their
types specified in format_string
when collected into the va_list.
See the GVariant varargs documentation.
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.
[skip]
Returns
a new, usually floating, GVariant
Since: 2.24
g_variant_new_boolean ()
GVariant *
g_variant_new_boolean (gboolean value);
Creates a new boolean GVariant instance -- either TRUE or FALSE.
Returns
a floating reference to a new boolean GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_byte ()
GVariant *
g_variant_new_byte (guint8 value);
Creates a new byte GVariant instance.
Returns
a floating reference to a new byte GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_int16 ()
GVariant *
g_variant_new_int16 (gint16 value);
Creates a new int16 GVariant instance.
Returns
a floating reference to a new int16 GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_uint16 ()
GVariant *
g_variant_new_uint16 (guint16 value);
Creates a new uint16 GVariant instance.
Returns
a floating reference to a new uint16 GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_int32 ()
GVariant *
g_variant_new_int32 (gint32 value);
Creates a new int32 GVariant instance.
Returns
a floating reference to a new int32 GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_uint32 ()
GVariant *
g_variant_new_uint32 (guint32 value);
Creates a new uint32 GVariant instance.
Returns
a floating reference to a new uint32 GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_int64 ()
GVariant *
g_variant_new_int64 (gint64 value);
Creates a new int64 GVariant instance.
Returns
a floating reference to a new int64 GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_uint64 ()
GVariant *
g_variant_new_uint64 (guint64 value);
Creates a new uint64 GVariant instance.
Returns
a floating reference to a new uint64 GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_handle ()
GVariant *
g_variant_new_handle (gint32 value);
Creates a new handle GVariant instance.
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.
Returns
a floating reference to a new handle GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_double ()
GVariant *
g_variant_new_double (gdouble value);
Creates a new double GVariant instance.
Returns
a floating reference to a new double GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_string ()
GVariant *
g_variant_new_string (const gchar *string);
Creates a string GVariant with the contents of string
.
string
must be valid UTF-8, and must not be NULL. To encode
potentially-NULL strings, use g_variant_new() with ms as the
format string.
Returns
a floating reference to a new string GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_take_string ()
GVariant *
g_variant_new_take_string (gchar *string);
Creates a string GVariant with the contents of string
.
string
must be valid UTF-8, and must not be NULL. To encode
potentially-NULL strings, use this with g_variant_new_maybe().
This function consumes string
. g_free() will be called on string
when it is no longer required.
You must not modify or access string
in any other way after passing
it to this function. It is even possible that string
is immediately
freed.
[skip]
Returns
a floating reference to a new string
GVariant instance.
[transfer none]
Since: 2.38
g_variant_new_printf ()
GVariant *
g_variant_new_printf (const gchar *format_string,
...);
Creates a string-type GVariant using printf formatting.
This is similar to calling g_strdup_printf() and then
g_variant_new_string() but it saves a temporary variable and an
unnecessary copy.
[skip]
Returns
a floating reference to a new string
GVariant instance.
[transfer none]
Since: 2.38
g_variant_new_object_path ()
GVariant *
g_variant_new_object_path (const gchar *object_path);
Creates a D-Bus object path GVariant with the contents of string
.
string
must be a valid D-Bus object path. Use
g_variant_is_object_path() if you're not sure.
Returns
a floating reference to a new object path GVariant instance.
[transfer none]
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 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.
Returns
TRUE if string
is a D-Bus object path
Since: 2.24
g_variant_new_signature ()
GVariant *
g_variant_new_signature (const gchar *signature);
Creates a D-Bus type signature GVariant with the contents of
string
. string
must be a valid D-Bus type signature. Use
g_variant_is_signature() if you're not sure.
Returns
a floating reference to a new signature GVariant instance.
[transfer none]
Since: 2.24
g_variant_is_signature ()
gboolean
g_variant_is_signature (const gchar *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.
Returns
TRUE if string
is a D-Bus type signature
Since: 2.24
g_variant_new_variant ()
GVariant *
g_variant_new_variant (GVariant *value);
Boxes value
. The result is a GVariant instance representing a
variant containing the original value.
If child
is a floating reference (see g_variant_ref_sink()), the new
instance takes ownership of child
.
[constructor]
Returns
a floating reference to a new variant GVariant instance.
[transfer none]
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 -1 then strv
is NULL-terminated.
Returns
a new floating GVariant instance.
[transfer none]
Since: 2.24
g_variant_new_bytestring ()
GVariant *
g_variant_new_bytestring (const gchar *string);
Creates an array-of-bytes GVariant with the contents of string
.
This function is just like g_variant_new_string() except that the
string need not be valid UTF-8.
The nul terminator character at the end of the string is stored in
the array.
Returns
a floating reference to a new bytestring GVariant instance.
[transfer none]
Since: 2.26
g_variant_new_bytestring_array ()
GVariant *
g_variant_new_bytestring_array (const gchar * const *strv,
gssize length);
Constructs an array of bytestring GVariant from the given array of
strings.
If length
is -1 then strv
is NULL-terminated.
Returns
a new floating GVariant instance.
[transfer none]
Since: 2.26
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 ()
guint8
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 D-Bus message. If you're not interacting
with D-Bus, 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.
The string will always be UTF-8 encoded, and will never be NULL.
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.
Returns
the constant string, UTF-8 encoded.
[transfer none]
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 string will always be UTF-8 encoded.
The return value must be freed using g_free().
Returns
a newly allocated string, UTF-8 encoded.
[transfer full]
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
.
Returns
the item contained in the variant.
[transfer full]
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.
Returns
an array of constant strings.
[array length=length zero-terminated=1][transfer container]
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.
Returns
an array of strings.
[array length=length zero-terminated=1][transfer full]
Since: 2.24
g_variant_get_objv ()
const gchar **
g_variant_get_objv (GVariant *value,
gsize *length);
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.
Returns
an array of constant strings.
[array length=length zero-terminated=1][transfer container]
Since: 2.30
g_variant_dup_objv ()
gchar **
g_variant_dup_objv (GVariant *value,
gsize *length);
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.
Returns
an array of strings.
[array length=length zero-terminated=1][transfer full]
Since: 2.30
g_variant_get_bytestring ()
const gchar *
g_variant_get_bytestring (GVariant *value);
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.
Returns
the constant string.
[transfer none][array zero-terminated=1][element-type guint8]
Since: 2.26
g_variant_dup_bytestring ()
gchar *
g_variant_dup_bytestring (GVariant *value,
gsize *length);
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().
Returns
a newly allocated string.
[transfer full][array zero-terminated=1 length=length][element-type guint8]
Since: 2.26
g_variant_get_bytestring_array ()
const gchar **
g_variant_get_bytestring_array (GVariant *value,
gsize *length);
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.
Returns
an array of constant strings.
[array length=length][transfer container]
Since: 2.26
g_variant_dup_bytestring_array ()
gchar **
g_variant_dup_bytestring_array (GVariant *value,
gsize *length);
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.
Returns
an array of strings.
[array length=length][transfer full]
Since: 2.26
g_variant_new_maybe ()
GVariant *
g_variant_new_maybe (const GVariantType *child_type,
GVariant *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
.
Returns
a floating reference to a new GVariant maybe instance.
[transfer none]
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.
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().
Returns
a floating reference to a new GVariant array.
[transfer none]
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.
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().
Returns
a floating reference to a new GVariant tuple.
[transfer none]
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).
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().
[constructor]
Returns
a floating reference to a new dictionary entry GVariant.
[transfer none]
Since: 2.24
g_variant_new_fixed_array ()
GVariant *
g_variant_new_fixed_array (const GVariantType *element_type,
gconstpointer elements,
gsize n_elements,
gsize element_size);
Constructs a new array GVariant instance, where the elements are
of element_type
type.
elements
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
must be the length of the elements
array.
Returns
a floating reference to a new array GVariant instance.
[transfer none]
Since: 2.32
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.
Returns
the contents of value
, or NULL.
[nullable][transfer full]
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).
Returns
the number of children in the container
Since: 2.24
g_variant_get_child_value ()
GVariant *
g_variant_get_child_value (GVariant *value,
gsize index_);
Reads a child item out of a container GVariant instance. This
includes variants, maybes, arrays, tuples and dictionary
entries. It is an error to call this function on any other type of
GVariant.
It is an error if index_
is greater than the number of child items
in the container. See g_variant_n_children().
The returned value is never floating. You should free it with
g_variant_unref() when you're done with it.
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).
Returns
the child at the specified index.
[transfer full]
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().
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.
[skip]
Since: 2.24
g_variant_lookup_value ()
GVariant *
g_variant_lookup_value (GVariant *dictionary,
const gchar *key,
const GVariantType *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.
Returns
the value of the dictionary key, or NULL.
[transfer full]
Since: 2.28
g_variant_lookup ()
gboolean
g_variant_lookup (GVariant *dictionary,
const gchar *key,
const gchar *format_string,
...);
Looks up a value in a dictionary GVariant.
This function is a wrapper around g_variant_lookup_value() and
g_variant_get(). In the case that NULL would have been returned,
this function returns FALSE. Otherwise, it unpacks the returned
value and returns TRUE.
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.
This function is currently implemented with a linear scan. If you
plan to do many lookups then GVariantDict may be more efficient.
[skip]
Returns
TRUE if a value was unpacked
Since: 2.28
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,
as given by the section on
serialized 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 the size
the appropriate type:
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.
Returns
a pointer to
the fixed array.
[array length=n_elements][transfer none]
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.
Returns
the serialised size of value
Since: 2.24
g_variant_get_data ()
gconstpointer
g_variant_get_data (GVariant *value);
Returns a pointer to the serialised form of a GVariant instance.
The returned data may not be in fully-normalised form if read from an
untrusted source. The returned data must not be freed; it remains
valid for as long as value
exists.
If value
is a fixed-sized value that was deserialised from a
corrupted serialised container then NULL may be returned. In this
case, the proper thing to do is typically to use the appropriate
number of nul bytes in place of value
. If value
is not fixed-sized
then NULL is never returned.
In the case that value
is already in serialised form, this function
is O(1). If the value is not already in serialised form,
serialisation occurs implicitly and is approximately O(n) in the size
of the result.
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).
Returns
the serialised form of value
, or NULL.
[transfer none]
Since: 2.24
g_variant_get_data_as_bytes ()
GBytes *
g_variant_get_data_as_bytes (GVariant *value);
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.
Returns
A new GBytes representing the variant data.
[transfer full]
Since: 2.36
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_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
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.
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.
Note: data
must be backed by memory that is aligned appropriately for the
type
being loaded. Otherwise this function will internally create a copy of
the memory (since GLib 2.60) or (in older versions) fail and exit the
process.
Returns
a new floating GVariant of type type
.
[transfer none]
Since: 2.24
g_variant_new_from_bytes ()
GVariant *
g_variant_new_from_bytes (const GVariantType *type,
GBytes *bytes,
gboolean 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
.
The data in bytes
must be aligned appropriately for the type
being loaded.
Otherwise this function will internally create a copy of the memory (since
GLib 2.60) or (in older versions) fail and exit the process.
Returns
a new GVariant with a floating reference.
[transfer none]
Since: 2.36
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).
While this function can safely handle untrusted, non-normal data, it is
recommended to check whether the input is in normal form beforehand, using
g_variant_is_normal_form(), and to reject non-normal inputs if your
application can be strict about what inputs it rejects.
The returned value is always in normal form and is marked as trusted.
Returns
the byteswapped form of value
.
[transfer full]
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
. The non-normal parts of
value
will be replaced with default values which are guaranteed to be in
normal form.
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.
Returns
a trusted GVariant.
[transfer full]
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_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.
Returns
TRUE if value
is in normal form
Since: 2.24
g_variant_hash ()
guint
g_variant_hash (gconstpointer value);
Generates a hash value for a GVariant instance.
The output of this function is guaranteed to be the same for a given
value only per-process. It may change between different processor
architectures or even different versions of GLib. Do not use this
function as a basis for building protocols or file formats.
The type of value
is gconstpointer only to allow use of this
function with GHashTable. value
must be a GVariant.
Returns
a hash value corresponding to value
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().
The format is described here.
If type_annotate
is TRUE, then type information is included in
the output.
Returns
a newly-allocated string holding the result.
[transfer full]
Since: 2.24
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_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.
[skip]
Returns
the number of items in value
Since: 2.24
g_variant_iter_n_children ()
gsize
g_variant_iter_n_children (GVariantIter *iter);
Queries the number of child items in the container that we are
iterating over. This is the total number of items -- not the number
of items remaining.
This function might be useful for preallocation of arrays.
Returns
the number of children in the container
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.
Here is an example for memory management with g_variant_iter_next():
For a solution that is likely to be more convenient to C programmers
when dealing with loops, see g_variant_iter_loop().
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.
[skip]
Returns
TRUE if a value was unpacked, or FALSE if there as no value
Since: 2.24
g_variant_iter_loop ()
gboolean
g_variant_iter_loop (GVariantIter *iter,
const gchar *format_string,
...);
Gets the next item in the container and unpacks it into the variable
argument list according to format_string
, returning TRUE.
If no more items remain then FALSE is returned.
On the first call to this function, the pointers appearing on the
variable argument list are assumed to point at uninitialised memory.
On the second and later calls, it is assumed that the same pointers
will be given and that they will point to the memory as set by the
previous call to this function. This allows the previous values to
be freed, as appropriate.
This function is intended to be used with a while loop as
demonstrated in the following example. This function can only be
used when iterating over an array. It is only valid to call this
function with a string constant for the format string and the same
string constant must be used each time. Mixing calls to this
function and g_variant_iter_next() or g_variant_iter_next_value() on
the same iterator causes undefined behavior.
If you break out of a such a while loop using g_variant_iter_loop() then
you must free or unreference all the unpacked values as you would with
g_variant_get(). Failure to do so will cause a memory leak.
Here is an example for memory management with g_variant_iter_loop():
For most cases you should use g_variant_iter_next().
This function is really only useful when unpacking into GVariant or
GVariantIter in order to allow you to skip the call to
g_variant_unref() or g_variant_iter_free().
For example, if you are only looping over simple integer and string
types, g_variant_iter_next() is definitely preferred. For string
types, use the '&' prefix to avoid allocating any memory at all (and
thereby avoiding the need to free anything as well).
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.
[skip]
Returns
TRUE if a value was unpacked, or FALSE if there was no
value
Since: 2.24
G_VARIANT_BUILDER_INIT()
#define G_VARIANT_BUILDER_INIT(variant_type) { { { 2942751021u, variant_type, { 0, } } } }
A stack-allocated GVariantBuilder must be initialized if it is
used together with g_auto() to avoid warnings or crashes if
function returns before g_variant_builder_init() is called on the
builder. This macro can be used as initializer instead of an
explicit zeroing a variable when declaring it and a following
g_variant_builder_init(), but it cannot be assigned to a variable.
The passed variant_type
should be a static GVariantType to avoid
lifetime issues, as copying the variant_type
does not happen in
the G_VARIANT_BUILDER_INIT() call, but rather in functions that
make sure that GVariantBuilder is valid.
Since: 2.50
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.
Returns
a new reference to builder
.
[transfer full]
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.
If value
is a floating reference (see g_variant_ref_sink()),
the builder
instance takes ownership of value
.
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().
Note that the arguments must be of the correct width for their types
specified in format_string
. This can be achieved by casting them. See
the GVariant varargs documentation.
This function might be used as follows:
[skip]
Since: 2.24
g_variant_builder_add_parsed ()
void
g_variant_builder_add_parsed (GVariantBuilder *builder,
const gchar *format,
...);
Adds to a GVariantBuilder.
This call is a convenience wrapper that is exactly equivalent to
calling g_variant_new_parsed() followed by
g_variant_builder_add_value().
Note that the arguments must be of the correct width for their types
specified in format_string
. This can be achieved by casting them. See
the GVariant varargs documentation.
This function might be used as follows:
Since: 2.26
g_variant_builder_end ()
GVariant *
g_variant_builder_end (GVariantBuilder *builder);
Ends the builder process and returns the constructed value.
It is not permissible to use builder
in any way after this call
except for reference counting operations (in the case of a
heap-allocated GVariantBuilder) or by reinitialising it with
g_variant_builder_init() (in the case of stack-allocated). This
means that for the stack-allocated builders there is no need to
call g_variant_builder_clear() after the call to
g_variant_builder_end().
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.
Returns
a new, floating, GVariant.
[transfer none]
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. type
is the type of the container: so to build a tuple of several values, type
must include the tuple itself.
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).
Example of building a nested variant:
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_DICT_INIT()
#define G_VARIANT_DICT_INIT(asv) { { { asv, 3488698669u, { 0, } } } }
A stack-allocated GVariantDict must be initialized if it is used
together with g_auto() to avoid warnings or crashes if function
returns before g_variant_dict_init() is called on the builder.
This macro can be used as initializer instead of an explicit
zeroing a variable when declaring it and a following
g_variant_dict_init(), but it cannot be assigned to a variable.
The passed asv
has to live long enough for GVariantDict to gather
the entries from, as the gathering does not happen in the
G_VARIANT_DICT_INIT() call, but rather in functions that make sure
that GVariantDict is valid. In context where the initialization
value has to be a constant expression, the only possible value of
asv
is NULL. It is still possible to call g_variant_dict_init()
safely with a different asv
right after the variable was
initialized with G_VARIANT_DICT_INIT().
Since: 2.50
g_variant_dict_unref ()
void
g_variant_dict_unref (GVariantDict *dict);
Decreases the reference count on dict
.
In the event that there are no more references, releases all memory
associated with the GVariantDict.
Don't call this on stack-allocated GVariantDict instances or bad
things will happen.
Since: 2.40
g_variant_dict_ref ()
GVariantDict *
g_variant_dict_ref (GVariantDict *dict);
Increases the reference count on dict
.
Don't call this on stack-allocated GVariantDict instances or bad
things will happen.
Returns
a new reference to dict
.
[transfer full]
Since: 2.40
g_variant_dict_init ()
void
g_variant_dict_init (GVariantDict *dict,
GVariant *from_asv);
Initialises a GVariantDict structure.
If from_asv
is given, it is used to initialise the dictionary.
This function completely ignores the previous contents of dict
. 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 GVariantDict you need to first
call g_variant_dict_clear() in order to avoid leaking memory.
You must not call g_variant_dict_ref() or g_variant_dict_unref() on a
GVariantDict that was initialised with this function. If you ever
pass a reference to a GVariantDict 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_dict_new() instead of this function.
[skip]
Since: 2.40
g_variant_dict_clear ()
void
g_variant_dict_clear (GVariantDict *dict);
Releases all memory associated with a GVariantDict without freeing
the GVariantDict structure itself.
It typically only makes sense to do this on a stack-allocated
GVariantDict if you want to abort building the value part-way
through. This function need not be called if you call
g_variant_dict_end() and it also doesn't need to be called on dicts
allocated with g_variant_dict_new (see g_variant_dict_unref() for
that).
It is valid to call this function on either an initialised
GVariantDict or one that was previously cleared by an earlier call
to g_variant_dict_clear() but it is not valid to call this function
on uninitialised memory.
Since: 2.40
g_variant_dict_contains ()
gboolean
g_variant_dict_contains (GVariantDict *dict,
const gchar *key);
Checks if key
exists in dict
.
Returns
TRUE if key
is in dict
Since: 2.40
g_variant_dict_lookup ()
gboolean
g_variant_dict_lookup (GVariantDict *dict,
const gchar *key,
const gchar *format_string,
...);
Looks up a value in a GVariantDict.
This function is a wrapper around g_variant_dict_lookup_value() and
g_variant_get(). In the case that NULL would have been returned,
this function returns FALSE. Otherwise, it unpacks the returned
value and returns TRUE.
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.
Returns
TRUE if a value was unpacked
Since: 2.40
g_variant_dict_lookup_value ()
GVariant *
g_variant_dict_lookup_value (GVariantDict *dict,
const gchar *key,
const GVariantType *expected_type);
Looks up a value in a GVariantDict.
If key
is not found in dictionary
, NULL is returned.
The expected_type
string specifies what type of value is expected.
If the value associated with key
has a different type then 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.
Returns
the value of the dictionary key, or NULL.
[transfer full]
Since: 2.40
g_variant_dict_insert_value ()
void
g_variant_dict_insert_value (GVariantDict *dict,
const gchar *key,
GVariant *value);
Inserts (or replaces) a key in a GVariantDict.
value
is consumed if it is floating.
Since: 2.40
g_variant_dict_end ()
GVariant *
g_variant_dict_end (GVariantDict *dict);
Returns the current value of dict
as a GVariant of type
G_VARIANT_TYPE_VARDICT, clearing it in the process.
It is not permissible to use dict
in any way after this call except
for reference counting operations (in the case of a heap-allocated
GVariantDict) or by reinitialising it with g_variant_dict_init() (in
the case of stack-allocated).
Returns
a new, floating, GVariant.
[transfer none]
Since: 2.40
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 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. 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.
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.
Note that the arguments in app
must be of the correct width for their types
specified in format
when collected into the va_list. See
the GVariant varargs documentation.
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.
Returns
a new, usually floating, GVariant
g_variant_new_parsed ()
GVariant *
g_variant_new_parsed (const gchar *format,
...);
Parses format
and returns the result.
format
must be a text format GVariant with one extension: 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.
Note that the arguments must be of the correct width for their types
specified in format
. This can be achieved by casting them. See
the GVariant varargs documentation.
Consider this simple example:
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
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 "%@".
Returns
a new floating GVariant instance
g_variant_parse_error_print_context ()
gchar *
g_variant_parse_error_print_context (GError *error,
const gchar *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:
or
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.
Returns
the printed message.
[transfer full]
Since: 2.40