Name
Generic Values -- A polymorphic type that can hold values of any other type.
Synopsis
#include <gobject.h>
#define G_VALUE_HOLDS (value,type)
#define G_VALUE_TYPE (value)
#define G_VALUE_TYPE_NAME (value)
#define G_TYPE_IS_VALUE (type)
#define G_TYPE_IS_VALUE_ABSTRACT (type)
#define G_IS_VALUE (value)
void (*GValueExchange) (GValue *value1,
GValue *value2);
struct GValue;
#define G_TYPE_VALUE
#define G_TYPE_VALUE_ARRAY
GValue* g_value_init (GValue *value,
GType g_type);
void g_value_copy (const GValue *src_value,
GValue *dest_value);
GValue* g_value_reset (GValue *value);
void g_value_unset (GValue *value);
gboolean g_value_fits_pointer (const GValue *value);
gpointer g_value_peek_pointer (const GValue *value);
gboolean g_value_type_compatible (GType src_type,
GType dest_type);
gboolean g_value_type_transformable (GType src_type,
GType dest_type);
gboolean g_value_transform (const GValue *src_value,
GValue *dest_value);
void (*GValueTransform) (const GValue *src_value,
GValue *dest_value);
void g_value_register_transform_func (GType src_type,
GType dest_type,
GValueTransform transform_func);
gchar* g_strdup_value_contents (const GValue *value);
|
Description
The GValue structure is basically a variable container that consists
of a type identifier and a specific value of that type.
The type identifier within a GValue structure always determines the
type of the associated value.
To create a undefined GValue structure, simply create a zero-filled
GValue structure. To initialize the GValue, use the g_value_init()
function. A GValue cannot be used until it is initialized.
The basic type operations (such as freeing and copying) are determined
by the GTypeValueTable associated with the type ID stored in the GValue.
Other GValue operations (such as converting values between types) are
provided by this interface.
Details
G_VALUE_HOLDS()
#define G_VALUE_HOLDS(value,type) (G_TYPE_CHECK_VALUE_TYPE ((value), (type))) |
Returns TRUE if value holds (or contains) a value of type.
This macro will also check for value != NULL and issue a
warning if the check fails.
G_VALUE_TYPE()
#define G_VALUE_TYPE(value) (((GValue*) (value))->g_type) |
Returns the type identifier of value.
G_VALUE_TYPE_NAME()
#define G_VALUE_TYPE_NAME(value) (g_type_name (G_VALUE_TYPE (value))) |
Returns the type name of value.
G_TYPE_IS_VALUE()
#define G_TYPE_IS_VALUE(type) (g_type_check_is_value_type (type)) |
Return whether the passed in type ID can be used for g_value_init().
That is, this macro checks whether this type provides an implementation
of the GTypeValueTable functions required for a type to create a GValue of.
G_TYPE_IS_VALUE_ABSTRACT()
#define G_TYPE_IS_VALUE_ABSTRACT(type) (g_type_test_flags ((type), G_TYPE_FLAG_VALUE_ABSTRACT)) |
G_IS_VALUE()
#define G_IS_VALUE(value) (G_TYPE_CHECK_VALUE (value)) |
Returns TRUE if value is a valid and initialized GValue structure.
struct GValue
struct GValue
{
/*< private >*/
GType g_type;
/* public for GTypeValueTable methods */
union {
gint v_int;
guint v_uint;
glong v_long;
gulong v_ulong;
gint64 v_int64;
guint64 v_uint64;
gfloat v_float;
gdouble v_double;
gpointer v_pointer;
} data[4];
}; |
A mostly opaque structure used to hold a GValue object. Mostly because
the data within the structure has protected scope: it is accessible only
to functions within a GTypeValueTable structure, or implementations of
the g_value_*() API.
G_TYPE_VALUE
#define G_TYPE_VALUE (g_value_get_type ()) |
G_TYPE_VALUE_ARRAY
#define G_TYPE_VALUE_ARRAY (g_value_array_get_type ()) |
g_value_init ()
Initializes value with the default value of type.
g_value_copy ()
void g_value_copy (const GValue *src_value,
GValue *dest_value); |
Copies the value of src_value into dest_value.
g_value_reset ()
Clears the current value in value and resets it to the default value
(as if the value had just been initialized).
g_value_unset ()
void g_value_unset (GValue *value); |
Clears the current value in value and "unsets" the type,
this releases all resources associated with this GValue.
An unset value is the same as an uninitialized (zero-filled)
GValue structure.
g_value_fits_pointer ()
Determines if value will fit inside the size of a pointer value.
This is an internal function introduced mainly for C marshallers.
g_value_peek_pointer ()
Return the value contents as pointer. This function asserts that
g_value_fits_pointer() returned TRUE for the passed in value.
This is an internal function introduced mainly for C marshallers.
g_value_type_compatible ()
g_value_type_transformable ()
GValueTransform ()
void (*GValueTransform) (const GValue *src_value,
GValue *dest_value); |
g_value_register_transform_func ()
g_strdup_value_contents ()
See Also
The fundamental types which all support GValue operations and thus
can be used as a type initializer for g_value_init() are defined by
a separate interface. See the Standard Values API for details.