Generic Values

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[2];
};

An opaque structure used to hold different types of values. 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. That is, code portions which implement new fundamental types. GValue users can not make any assumptions about how data is stored within the 2 element GValue.data[] union, and the g_type member should only be accessed through the G_VALUE_TYPE() macro.

G_TYPE_VALUE

#define	G_TYPE_VALUE		(g_value_get_type ())

Returns the type ID of the "GValue" type which is a boxed type, used to pass around pointers to GValues.

G_TYPE_VALUE_ARRAY

#define	G_TYPE_VALUE_ARRAY	(g_value_array_get_type ())

Returns the type ID of the "GValueArray" type which is a boxed type, used to pass around pointers to GValueArrays.

g_value_init ()

GValue*     g_value_init                    (GValue *value,
                                             GType g_type);

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 ()

GValue*     g_value_reset                   (GValue *value);

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 ()

gboolean    g_value_fits_pointer            (const GValue *value);

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 ()

gpointer    g_value_peek_pointer            (const GValue *value);

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 ()

gboolean    g_value_type_compatible         (GType src_type,
                                             GType dest_type);

Returns whether a GValue of type src_type can be copied into a GValue of type dest_type.

g_value_type_transformable ()

gboolean    g_value_type_transformable      (GType src_type,
                                             GType dest_type);

Check whether g_value_transform() is able to transform values of type src_type into values of type dest_type.

g_value_transform ()

gboolean    g_value_transform               (const GValue *src_value,
                                             GValue *dest_value);

Tries to cast the contents of src_value into a type apropriate to store in dest_value, e.g. to transform a G_TYPE_INT value into a G_TYPE_FLOAT value. Performing transformations between value types might incour precision lossage. Especially transformations into strings might reveal seemingly arbitrary results and shouldn't be relied upon for production code (such as rcfile value or object property serialization).

GValueTransform ()

void        (*GValueTransform)              (const GValue *src_value,
                                             GValue *dest_value);

g_value_register_transform_func ()

void        g_value_register_transform_func (GType src_type,
                                             GType dest_type,
                                             GValueTransform transform_func);

g_strdup_value_contents ()

gchar*      g_strdup_value_contents         (const GValue *value);

Return a newly allocated string, which describes the contents of a GValue. The main purpose of this function is to describe GValue contents for debugging output, the way in which the contents are described may change between different GLib versions.