1 <!-- ##### SECTION Title ##### -->
4 <!-- ##### SECTION Short_Description ##### -->
5 The GLib Runtime type identification and management system
7 <!-- ##### SECTION Long_Description ##### -->
9 The GType API is the foundation of the GObject system. It provides the
10 facilities for registering and managing all fundamental data types,
11 user-defined object and interface types. Before using any GType
12 or GObject functions, g_type_init() must be called to initialize the
16 For type creation and registration purposes, all types fall into one of
17 two categories: static or dynamic. Static types are never loaded or
18 unloaded at run-time as dynamic types may be. Static types are created
19 with g_type_register_static() that gets type specific information passed
20 in via a #GTypeInfo structure.
21 Dynamic types are created with g_type_register_dynamic() which takes a
22 #GTypePlugin structure instead. The remaining type information (the
23 #GTypeInfo structure) is retrived during runtime through #GTypePlugin
24 and the g_type_plugin_*() API.
25 These registration functions are usually called only once from a
26 function whose only purpose is to return the type identifier for a
27 specific class. Once the type (or class or interface) is registered,
28 it may be instantiated, inherited, or implemented depending on exactly
29 what sort of type it is.
30 There is also a third registration function for registering fundamental
31 types called g_type_register_fundamental() which requires both a #GTypeInfo
32 structure and a GTypeFundamentalInfo structure but it is seldom used
33 since most fundamental types are predefined rather than user-defined.
36 <!-- ##### SECTION See_Also ##### -->
41 <!-- ##### TYPEDEF GType ##### -->
43 A numerical value which represents the unique identifier of a registered
48 <!-- ##### MACRO G_TYPE_FUNDAMENTAL ##### -->
50 Returns #TRUE if @type is a fundamental data type such as #G_TYPE_INT or
51 #G_TYPE_POINTER. Fundamental types are types that serve as fundaments for
52 the derived types, thus they are the roots of distinct inheritance hierarchies.
55 @type: A #GType value.
58 <!-- ##### MACRO G_TYPE_FUNDAMENTAL_MAX ##### -->
60 An integer constant that represents the number of identifiers reserved
61 for types that are assigned at compile-time.
66 <!-- ##### MACRO G_TYPE_DERIVE_ID ##### -->
75 <!-- ##### MACRO G_TYPE_BRANCH_SEQNO ##### -->
83 <!-- ##### MACRO G_TYPE_FUNDAMENTAL_LAST ##### -->
90 <!-- ##### MACRO G_TYPE_IS_ABSTRACT ##### -->
92 Returns #TRUE if @type is an abstract type. An abstract type can not be
93 instantiated and is normally used as an abstract base class for
97 @type: A #GType value.
100 <!-- ##### MACRO G_TYPE_IS_DERIVED ##### -->
102 Returns #TRUE if @type is derived (or in object-oriented terminology:
103 inherited) from another type (this holds true for all non-fundamental
107 @type: A #GType value.
110 <!-- ##### MACRO G_TYPE_IS_FUNDAMENTAL ##### -->
112 Returns #TRUE if @type is a fundamental type.
115 @type: A #GType value.
118 <!-- ##### MACRO G_TYPE_IS_VALUE_TYPE ##### -->
123 @type: A #GType value.
126 <!-- ##### MACRO G_TYPE_IS_CLASSED ##### -->
128 Returns #TRUE if @type is a classed type.
131 @type: A #GType value.
134 <!-- ##### MACRO G_TYPE_IS_INSTANTIATABLE ##### -->
136 Returns #TRUE if @type can be instantiated. Instantiation is the
137 process of creating an instance (object) of this type.
140 @type: A #GType value.
143 <!-- ##### MACRO G_TYPE_IS_DERIVABLE ##### -->
145 Returns #TRUE if @type is a derivable type. A derivable type can
146 be used as the base class of a flat (single-level) class hierarchy.
149 @type: A #GType value.
152 <!-- ##### MACRO G_TYPE_IS_DEEP_DERIVABLE ##### -->
154 Returns #TRUE if @type is a deep derivable type. A deep derivable type
155 can be used as the base class of a deep (multi-level) class hierarchy.
158 @type: A #GType value.
161 <!-- ##### MACRO G_TYPE_IS_INTERFACE ##### -->
163 Returns #TRUE if @type is an interface type.
164 Interface types are types that provide pure APIs, the implementation
165 of which is provided by another type (which is then said to conform
166 to the interface). GLib interfaces are somewhat analogous to Java
167 interfaces and C++ classes containing only pure virtual functions.
170 @type: A #GType value.
173 <!-- ##### ENUM GTypeFundamentals ##### -->
175 The predefined identifiers of the reserved fundamental types.
178 @G_TYPE_INVALID: Usually a return value indicating an error.
179 @G_TYPE_NONE: A synonym for the "void" type in C.
180 @G_TYPE_INTERFACE: Root type of all interface types.
181 @G_TYPE_CHAR: Identifier for the built-in type "gchar".
182 @G_TYPE_UCHAR: Identifier for the built-in type "guchar".
183 @G_TYPE_BOOLEAN: Identifier for the built-in type "gboolean".
184 @G_TYPE_INT: Identifier for the built-in type "gint".
185 @G_TYPE_UINT: Identifier for the built-in type "guint".
186 @G_TYPE_LONG: Identifier for the built-in type "glong".
187 @G_TYPE_ULONG: Identifier for the built-in type "gulong".
190 @G_TYPE_ENUM: Identifier for the "#GEnum" type.
191 @G_TYPE_FLAGS: Identifier for the "#GFlags" type.
192 @G_TYPE_FLOAT: Identifier for the built-in type "gfloat".
193 @G_TYPE_DOUBLE: Identifier for the built-in type "gdouble".
194 @G_TYPE_STRING: Identifier for a pointer to a null-terminated string "gchar*".
195 @G_TYPE_POINTER: Identifier for anonymous pointers "void*".
196 @G_TYPE_BOXED: Identifier for the "#GBoxed" type.
197 @G_TYPE_PARAM: Identifier for the "#GParam" type.
198 @G_TYPE_OBJECT: Identifier for the "#GObject" type.
199 @G_TYPE_RESERVED_GLIB_FIRST:
200 @G_TYPE_RESERVED_GLIB_LAST:
201 @G_TYPE_RESERVED_BSE_FIRST: First fundamental type ID reserved for BSE.
202 @G_TYPE_RESERVED_BSE_LAST: Last fundamental type ID reserved for BSE.
203 @G_TYPE_RESERVED_USER_FIRST:
205 <!-- ##### STRUCT GTypeInterface ##### -->
207 An opaque structure used as the base of all interface types.
211 <!-- ##### STRUCT GTypeInstance ##### -->
213 An opaque structure used as the base of all type instances.
217 <!-- ##### STRUCT GTypeInfo ##### -->
219 This structure is used to provide the type system with the information
220 required to initialize and destruct (finalize) a type's class and
222 The initialized structure is passed to the g_type_register_static() function
223 (or is copied into the provided #GTypeInfo structure in the
224 g_type_plugin_complete_type_info()). The type system will perform a deep
225 copy of this structure, so it's memory does not need to be persistent
226 across invocation of g_type_register_static().
229 @class_size: Size of the class structure (required for interface, classed and instantiatable types).
230 @base_init: Location of the base initialization function (optional).
231 @base_finalize: Location of the base finalization function (optional).
232 @class_init: Location of the class initialization function (optional, for classed and instantiatable types only).
233 @class_finalize: Location of the class finalization function (optional).
234 @class_data: User-supplied data passed to the class init/finalize functions.
235 @instance_size: Size of the instance (object) structure (required for instantiatable types only).
236 @n_preallocs: Number of pre-allocated (cached) instances to reserve memory for (0 indicates no caching).
237 @instance_init: Location of the instance initialization function (optional, for instantiatable types only).
238 @value_table: A #GTypeValueTable function table for generic handling of GValues of this type (usualy only
239 useful for fundamental types).
241 <!-- ##### STRUCT GTypeFundamentalInfo ##### -->
243 A structure that provides information to the type system which is
244 used specifically for managing fundamental types.
249 <!-- ##### STRUCT GInterfaceInfo ##### -->
251 A structure that provides information to the type system which is
252 used specifically for managing interface types.
255 @interface_init: Location of the function that initializes the interface.
256 @interface_finalize: Location of the function that finalizes the interface.
257 @interface_data: Location of user data passed to the @interface_init and
258 @interface_finalize functions (optional).
260 <!-- ##### STRUCT GTypeValueTable ##### -->
262 The #GTypeValueTable provides the functions required by the #GValue implementation,
263 to serve as a container for values of a type.
266 @value_init: Default initialize @values contents by poking values
267 directly into the value->data array. The data array of
268 the #GValue passed into this function was zero-filled
269 with memset, so no care has to be taken to free any
270 old contents. E.g. for the implementation of a string
271 value that may never be NULL, the implementation might
273 <msgtext><programlisting>
275 value->data[0].v_pointer = g_strdup ("");
277 </programlisting></msgtext>
278 @value_free: Free any old contents that might be left in the
279 data array of the passed in @value. No resources may
280 remain allocated through the #GValue contents after
281 this function returns. E.g. for our above string type:
282 <msgtext><programlisting>
284 /* only free strings without a specific flag for static storage */
285 if (!(value->data[1].v_uint & G_VALUE_NOCOPY_CONTENTS))
286 g_free (value->data[0].v_pointer);
288 </programlisting></msgtext>
289 @value_copy: @dest_value is a #GValue with zero-filled data section
290 and @src_value is a properly setup #GValue of same or
292 The purpose of this function is to copy the contents of
293 @src_value into @dest_value in a way, that even after
294 @src_value has been freed, the contents of @dest_value
295 remain valid. String type example:
296 <msgtext><programlisting>
298 dest_value->data[0].v_pointer = g_strdup (src_value->data[0].v_pointer);
300 </programlisting></msgtext>
301 @value_peek_pointer: If the value contents fit into a pointer, such as objects
302 or strings, return this pointer, so the caller can peek at
303 the current contents. To extend on our above string example:
304 <msgtext><programlisting>
306 return value->data[0].v_pointer;
308 </programlisting></msgtext>
309 @collect_format: A string format describing how to collect the contents of
310 this value, bit-by-bit. Each character in the format represents
311 an argument to be collected, the characters themselves indicate
312 the type of the argument. Currently supported arguments are:
313 <msgtext><variablelist>
314 <varlistentry><term></term><listitem><para>
315 'i' - Integers. passed as collect_values[].v_int.
316 </para></listitem></varlistentry>
317 <varlistentry><term></term><listitem><para>
318 'l' - Longs. passed as collect_values[].v_long.
319 </para></listitem></varlistentry>
320 <varlistentry><term></term><listitem><para>
321 'd' - Doubles. passed as collect_values[].v_double.
322 </para></listitem></varlistentry>
323 <varlistentry><term></term><listitem><para>
324 'p' - Pointers. passed as collect_values[].v_pointer.
325 </para></listitem></varlistentry>
326 </variablelist></msgtext>
327 It should be noted, that for variable argument list construction,
328 ANSI C promotes every type smaller than an integer to an int, and
329 floats to doubles. So for collection of short int or char, 'i'
330 needs to be used, and for collection of floats 'd'.
331 @collect_value: The collect_value() function is responsible for converting the
332 values collected from a variable argument list into contents
333 suitable for storage in a GValue. This function should setup
334 @value similar to value_init(), e.g. for a string value that
335 does not allow NULL pointers, it needs to either spew an error,
336 or do an implicit conversion by storing an empty string.
337 The @value passed in to this function has a zero-filled data
338 array, so just like for @value_init it is guaranteed to not
339 contain any old contents that might need freeing.
340 @n_collect_values is exactly the string length of @collect_format,
341 and @collect_values is an array of unions #GTypeCValue with
342 length @n_collect_values, containing the collected values
343 according to @collect_format.
344 @collect_flags is an argument provided as a hint by the caller,
345 which may contain the flag #G_VALUE_NOCOPY_CONTENTS indicating,
346 that the collected value contents may be considered "static"
347 for the duration of the #@value lifetime.
348 Thus an extra copy of the contents stored in @collect_values is
349 not required for assignment to @value.
350 For our above string example, we continue with:
351 <msgtext><programlisting>
353 if (!collect_values[0].v_pointer)
354 value->data[0].v_pointer = g_strdup ("");
355 else if (collect_flags & G_VALUE_NOCOPY_CONTENTS)
357 value->data[0].v_pointer = collect_values[0].v_pointer;
358 /* keep a flag for the value_free() implementation to not free this string */
359 value->data[1].v_uint = G_VALUE_NOCOPY_CONTENTS;
362 value->data[0].v_pointer = g_strdup (collect_values[0].v_pointer);
366 </programlisting></msgtext>
367 It should be noted, that it is generally a bad idea to follow the
368 #G_VALUE_NOCOPY_CONTENTS hint for reference counted types. Due to
369 reentrancy requirements and reference count assertions performed
370 by the GSignal code, reference counts should always be incremented
371 for reference counted contents stored in the value->data array.
372 To deviate from our string example for a moment, and taking a look
373 at an exemplary implementation for collect_value() of #GObject:
374 <msgtext><programlisting>
376 if (collect_values[0].v_pointer)
378 GObject *object = G_OBJECT (collect_values[0].v_pointer);
380 /* never honour G_VALUE_NOCOPY_CONTENTS for ref-counted types */
381 value->data[0].v_pointer = g_object_ref (object);
385 return g_strdup_printf ("Object passed as invalid NULL pointer");
387 </programlisting></msgtext>
388 The reference count for valid objects is always incremented,
389 regardless of @collect_flags. For invalid objects, the example
390 returns a newly allocated string without altering @value.
391 Upon success, collect_value() needs to return NULL, if however
392 a malicious condition occurred, collect_value() may spew an
393 error by returning a newly allocated non-NULL string, giving
394 a suitable description of the error condition.
395 The calling code makes no assumptions about the @value
396 contents being valid upon error returns, @value
397 is simply thrown away without further freeing. As such, it is
398 a good idea to not allocate #GValue contents, prior to returning
399 an error, however, collect_values() is not obliged to return
400 a correctly setup @value for error returns, simply because
401 any non-NULL return is considered a fatal condition so further
402 program behaviour is undefined.
403 @lcopy_format: Format description of the arguments to collect for @lcopy_value,
404 analogous to @collect_format. Usually, @lcopy_format string consists
405 only of 'p's to provide lcopy_value() with pointers to storage locations.
406 @lcopy_value: This function is responsible for storing the @value contents into
407 arguments passed through a variable argument list which got
408 collected into @collect_values according to @lcopy_format.
409 @n_collect_values equals the string length of @lcopy_format,
410 and @collect_flags may contain #G_VALUE_NOCOPY_CONTENTS.
411 In contrast to collect_value(), lcopy_value() is obliged to
412 always properly support #G_VALUE_NOCOPY_CONTENTS.
413 Similar to collect_value() the function may prematurely abort
414 by returning a newly allocated string describing an error condition.
415 To complete the string example:
416 <msgtext><programlisting>
418 gchar **string_p = collect_values[0].v_pointer;
421 return g_strdup_printf ("string location passed as NULL");
423 if (collect_flags & G_VALUE_NOCOPY_CONTENTS)
424 *string_p = value->data[0].v_pointer;
426 *string_p = g_strdup (value->data[0].v_pointer);
429 </programlisting></msgtext>
430 And an exemplary version of lcopy_value() for
431 reference-counted types:
432 <msgtext><programlisting>
434 GObject **object_p = collect_values[0].v_pointer;
437 return g_strdup_printf ("object location passed as NULL");
438 if (!value->data[0].v_pointer)
440 else if (collect_flags & G_VALUE_NOCOPY_CONTENTS) /* always honour */
441 *object_p = value->data[0].v_pointer;
443 *object_p = g_object_ref (value->data[0].v_pointer);
446 </programlisting></msgtext>
448 <!-- ##### MACRO G_TYPE_FROM_INSTANCE ##### -->
450 Returns the type identifier from a given @instance structure.
453 @instance: Location of a valid #GTypeInstance structure.
456 <!-- ##### MACRO G_TYPE_FROM_CLASS ##### -->
458 Returns the type identifier from a given @class structure.
461 @g_class: Location of a valid #GTypeClass structure.
464 <!-- ##### MACRO G_TYPE_FROM_INTERFACE ##### -->
466 Returns the type identifier from a given @interface structure.
469 @g_iface: Location of a valid #GTypeInterface structure.
472 <!-- ##### MACRO G_TYPE_INSTANCE_GET_CLASS ##### -->
474 Returns the class structure of a given @instance, casted
475 to a specified anchestor type @g_type of the instance.
478 @instance: Location of the #GTypeInstance structure.
479 @g_type: The anchestor type of the class to be returned.
480 @c_type: The corresponding C type of @g_Type.
483 <!-- ##### MACRO G_TYPE_INSTANCE_GET_INTERFACE ##### -->
493 <!-- ##### MACRO G_TYPE_CHECK_INSTANCE ##### -->
501 <!-- ##### MACRO G_TYPE_CHECK_INSTANCE_CAST ##### -->
511 <!-- ##### MACRO G_TYPE_CHECK_INSTANCE_TYPE ##### -->
520 <!-- ##### MACRO G_TYPE_CHECK_CLASS_CAST ##### -->
530 <!-- ##### MACRO G_TYPE_CHECK_CLASS_TYPE ##### -->
539 <!-- ##### MACRO G_TYPE_CHECK_VALUE ##### -->
547 <!-- ##### MACRO G_TYPE_CHECK_VALUE_TYPE ##### -->
556 <!-- ##### MACRO G_TYPE_FLAG_RESERVED_ID_BIT ##### -->
563 <!-- ##### FUNCTION g_type_init ##### -->
565 Prior to any use of the type system, g_type_init() has to be called to initialize
566 the type system and assorted other code portions (such as the various fundamental
567 type implementations or the signal system).
570 <!-- # Unused Parameters # -->
571 @debug_flags: Bitwise combination of #GTypeDebugFlags values for debugging purposes.
574 <!-- ##### FUNCTION g_type_init_with_debug_flags ##### -->
582 <!-- ##### FUNCTION g_type_name ##### -->
584 Return the unique name that is assigned to a type ID (this is the preferred method
585 to find out whether a specific type has been registered for the passed in ID yet).
588 @type: Type to return name for.
589 @Returns: Static type name or NULL.
592 <!-- ##### FUNCTION g_type_qname ##### -->
594 Return the corresponding quark of the type IDs name.
597 @type: Type to return quark of type name for.
598 @Returns: The type names quark or 0.
601 <!-- ##### FUNCTION g_type_from_name ##### -->
603 Lookup the type ID from a given type name, returns 0 if no type has been registered under this name
604 (this is the preferred method to find out by name whether a specific type has been registered yet).
607 @name: Type name to lookup.
608 @Returns: Corresponding type ID or 0.
611 <!-- ##### FUNCTION g_type_parent ##### -->
613 Return the direct parent type of the passed in type.
614 If the passed in type has no parent, i.e. is a fundamental type, 0 is returned.
617 @type: The derived type.
618 @Returns: The parent type.
621 <!-- ##### FUNCTION g_type_depth ##### -->
630 <!-- ##### FUNCTION g_type_next_base ##### -->
632 Given a @leaf_type and a @root_type which is contained in its anchestry, return
633 the type that @root_type is the immediate parent of.
634 In other words, this function determines the type that is derived directly from
635 @root_type which is also a base class of @leaf_type. Given a root type and a
636 leaf type, this function can be used to determine the types and order in which
637 the leaf type is descended from the root type.
640 @leaf_type: Descendant of @root_type and the type to be returned.
641 @root_type: Immediate parent of the returned type.
642 @Returns: Immediate child of @root_type and anchestor of @leaf_type.
645 <!-- ##### FUNCTION g_type_is_a ##### -->
647 Check whether @type is a descendant of @is_a_type.
650 @type: Type to check anchestry for.
651 @is_a_type: Possible anchestor of @type.
652 @Returns: %TRUE if @type is_a @is_a_type holds true.
655 <!-- ##### FUNCTION g_type_fundamental_branch_last ##### -->
664 <!-- ##### FUNCTION g_type_class_ref ##### -->
666 Increments the reference count of the class structure belonging to
667 @type. This function will demand-create the class if it doesn't
671 @type: Type ID of a classed type.
672 @Returns: The #GTypeClass structure for the given type ID.
675 <!-- ##### FUNCTION g_type_class_peek ##### -->
677 This function is essentially the same as g_type_class_ref(), except that
678 the classes reference count isn't incremented. Therefore, this function
679 may return NULL if the class of the type passed in does not currently
680 exist (hasn't been referenced before).
683 @type: Type ID of a classed type.
684 @Returns: The #GTypeClass structure for the given type ID or NULL
685 if the class does not currently exist.
688 <!-- ##### FUNCTION g_type_class_unref ##### -->
690 Decrements the reference count of the class structure being passed in.
691 Once the last reference count of a class has been released, classes
692 may be finalized by the type system, so further dereferencing of a
693 class pointer after g_type_class_unref() are invalid.
696 @g_class: The #GTypeClass structure to unreference.
699 <!-- ##### FUNCTION g_type_class_peek_parent ##### -->
701 This is a convenience function, often needed in class intializers.
702 It essentially takes the immediate parent type of the class passed in,
703 and returns the class structure thereof. Since derived classes hold
704 a reference count on their parent classes as long as they are instantiated,
705 the returned class will always exist. This function is essentially
708 <msgtext><programlisting>
709 g_type_class_peek (g_type_parent (G_TYPE_FROM_CLASS (g_class)));
710 </programlisting></msgtext>
714 @g_class: The #GTypeClass structure to retrieve the parent class for.
715 @Returns: The parent class of @g_class.
718 <!-- ##### FUNCTION g_type_interface_peek ##### -->
728 <!-- ##### FUNCTION g_type_interface_peek_parent ##### -->
737 <!-- ##### FUNCTION g_type_children ##### -->
739 Return a newly allocated and 0 terminated array of type IDs, listing the
740 child types of @type. The return value has to be g_free()ed after use.
743 @type: The parent type.
744 @n_children: Optional #guint pointer to contain the number of child types.
745 @Returns: Newly allocated and 0 terminated array of child types.
748 <!-- ##### FUNCTION g_type_interfaces ##### -->
750 Return a newly allocated and 0 terminated array of type IDs, listing the
751 interface types that @type conforms to. The return value has to be
752 g_free()ed after use.
755 @type: The type to list interface types for.
756 @n_interfaces: Optional #guint pointer to contain the number of interface types.
757 @Returns: Newly allocated and 0 terminated array of interface types.
760 <!-- ##### FUNCTION g_type_set_qdata ##### -->
770 <!-- ##### FUNCTION g_type_get_qdata ##### -->
780 <!-- ##### FUNCTION g_type_query ##### -->
789 <!-- ##### USER_FUNCTION GBaseInitFunc ##### -->
791 A callback function used by the type system to do base initialization
792 of the class structures of derived types. It is called as part of the
793 initialization process of all derived classes and should reallocate
794 or reset all dynamic class members copied over from the parent class.
795 Therefore class members, e.g. strings, that are not sufficiently
796 handled by a plain memory copy of the parent class into the derived class
797 have to be altered. See GClassInitFunc() for a discussion of the class
798 intialization process.
801 @g_class: The #GTypeClass structure to initialize.
804 <!-- ##### USER_FUNCTION GBaseFinalizeFunc ##### -->
806 A callback function used by the type system to finalize those portions
807 of a derived types class structure that were setup from the corresponding
808 GBaseInitFunc() function. Class finalization basically works the inverse
809 way in which class intialization is performed.
810 See GClassInitFunc() for a discussion of the class intialization process.
813 @g_class: The #GTypeClass structure to finalize.
816 <!-- ##### USER_FUNCTION GClassInitFunc ##### -->
818 A callback function used by the type system to initialize the class
819 of a specific type. This function should initialize all static class
821 The initialization process of a class involves:
823 <varlistentry><term></term><listitem><para>
824 1 - Copying common members from the parent class over to the
825 derived class structure.
826 </para></listitem></varlistentry>
827 <varlistentry><term></term><listitem><para>
828 2 - Zero initialization of the remaining members not copied
829 over from the parent class.
830 </para></listitem></varlistentry>
831 <varlistentry><term></term><listitem><para>
832 3 - Invocation of the GBaseInitFunc initializers of all parent
833 types and the class' type.
834 </para></listitem></varlistentry>
835 <varlistentry><term></term><listitem><para>
836 4 - Invocation of the class' GClassInitFunc initializer.
837 </para></listitem></varlistentry>
839 Since derived classes are partially initialized through a memory copy
840 of the parent class, the general rule is that GBaseInitFunc() and
841 GBaseFinalizeFunc() should take care of necessary reinitialization
842 and release of those class members that were introduced by the type
843 that specified these GBaseInitFunc()/GBaseFinalizeFunc().
844 GClassInitFunc() should only care about intializing static
845 class members, while dynamic class members (such as allocated strings
846 or reference counted resources) are better handled by a GBaseInitFunc()
847 for this type, so proper initialization of the dynamic class members
848 are performed for class intialization of derived types as well.
849 An example may help to correspond the intend of the different class
852 <msgtext><programlisting>
854 GObjectClass parent_class;
856 gchar *dynamic_string;
859 type_a_base_class_init (TypeAClass *class)
861 class->dynamic_string = g_strdup ("some string");
864 type_a_base_class_finalize (TypeAClass *class)
866 g_free (class->dynamic_string);
869 type_a_class_init (TypeAClass *class)
871 class->static_integer = 42;
875 TypeAClass parent_class;
877 GString *dynamic_gstring;
880 type_b_base_class_init (TypeBClass *class)
882 class->dynamic_gstring = g_string_new ("some other string);
885 type_b_base_class_finalize (TypeBClass *class)
887 g_string_free (class->dynamic_gstring);
890 type_b_class_init (TypeBClass *class)
892 class->static_float = 3.14159265358979323846;
894 </programlisting></msgtext>
895 Initialization of TypeBClass will first cause initialization of
896 TypeAClass (derived classes reference their parent classes, see
897 g_type_class_ref() on this).
898 Initialization of TypeAClass roughly involves zero-initializing its fields,
899 then calling its GBaseInitFunc() type_a_base_class_init() that allocates
900 its dynamic members (dynamic_string) and finally calling its GClassInitFunc()
901 type_a_class_init() to initialize its static members (static_integer).
902 The first step in the initialization process of TypeBClass is then
903 a plain memory copy of the contents of TypeAClass into TypeBClass and
904 zero-initialization of the remaining fields in TypeBClass.
905 The dynamic members of TypeAClass within TypeBClass now need
906 reinitialization which is performed by calling type_a_base_class_init()
907 with an argument of TypeBClass.
908 After that, the GBaseInitFunc() of TypeBClass, type_b_base_class_init()
909 is called to allocate the dynamic members of TypeBClass (dynamic_gstring),
910 and finally the GClassInitFunc() of TypeBClass, type_b_class_init(),
911 is called to complete the initialization process with the static members
913 Corresponding finalization counter parts to the GBaseInitFunc() functions
914 have to be provided to release allocated resources at class finalization
918 @g_class: The #GTypeClass structure to initialize.
919 @class_data: The @class_data member supplied via the #GTypeInfo structure.
922 <!-- ##### USER_FUNCTION GClassFinalizeFunc ##### -->
924 A callback function used by the type system to finalize a class.
925 This function is rarely needed, as dynamically allocated class resources
926 should be handled by GBaseInitFunc() and GBaseFinalizeFunc().
927 Also, specification of a GClassFinalizeFunc in the #GTypeInfo
928 structure of a static type is invalid, because classes of static types
929 will never be finalized (they are artificially kept alive when their
930 reference count drops to zero).
933 @g_class: The #GTypeClass structure to finalize.
934 @class_data: The @class_data member supplied via the #GTypeInfo structure.
937 <!-- ##### USER_FUNCTION GInstanceInitFunc ##### -->
939 A callback function used by the type system to initialize a new
940 instance of a type. This function initializes all instance members and
941 allocates any resources required by it.
942 Initialization of a derived instance involves calling all its parent
943 types instance initializers, therefore the class member of the instance
944 is altered during its initialization to always point to the class that
945 belongs to the type the current initializer was introduced for.
948 @instance: The instance to initialize.
949 @g_class: The class of the type the instance is created for.
952 <!-- ##### USER_FUNCTION GInterfaceInitFunc ##### -->
954 A callback function used by the type system to initialize a new
955 interface. This function should initialize all internal data and
956 allocate any resources required by the interface.
959 @g_iface: The interface structure to initialize.
960 @iface_data: The @class_data supplied via the #GTypeInfo structure.
963 <!-- ##### USER_FUNCTION GInterfaceFinalizeFunc ##### -->
965 A callback function used by the type system to finalize an interface.
966 This function should destroy any internal data and release any resources
967 allocated by the corresponding GInterfaceInitFunc() function.
970 @g_iface: The interface structure to finalize.
971 @iface_data: The @class_data supplied via the #GTypeInfo structure.
974 <!-- ##### USER_FUNCTION GTypeClassCacheFunc ##### -->
984 <!-- ##### ENUM GTypeFlags ##### -->
986 Bit masks used to check or determine characteristics of a type.
989 @G_TYPE_FLAG_ABSTRACT: Indicates an abstract type. No instances can be
990 created for an abstract type.
991 @G_TYPE_FLAG_VALUE_ABSTRACT:
993 <!-- ##### ENUM GTypeFundamentalFlags ##### -->
995 Bit masks used to check or determine specific characteristics of a
999 @G_TYPE_FLAG_CLASSED: Indicates a classed type.
1000 @G_TYPE_FLAG_INSTANTIATABLE: Indicates an instantiable type (implies classed).
1001 @G_TYPE_FLAG_DERIVABLE: Indicates a flat derivable type.
1002 @G_TYPE_FLAG_DEEP_DERIVABLE: Indicates a deep derivable type (implies derivable).
1004 <!-- ##### FUNCTION g_type_register_static ##### -->
1006 Registers @type_name as the name of a new static type derived from
1007 @parent_type. The type system uses the information contained in the
1008 #GTypeInfo structure pointed to by @info to manage the type and its
1009 instances (if not abstract). The value of @flags determines the nature
1010 (e.g. abstract or not) of the type.
1013 @parent_type: Type which this type will be derived from.
1014 @type_name: Null-terminated string used as the name of the new type.
1015 @info: The #GTypeInfo structure for this type.
1016 @flags: Bitwise combination of #GTypeFlags values.
1017 @Returns: The new type identifier.
1020 <!-- ##### FUNCTION g_type_register_dynamic ##### -->
1022 Registers @type_name as the name of a new dynamic type derived from
1023 @parent_type. The type system uses the information contained in the
1024 #GTypePlugin structure pointed to by @plugin to manage the type and its
1025 instances (if not abstract). The value of @flags determines the nature
1026 (e.g. abstract or not) of the type.
1029 @parent_type: Type which this type will be derived from.
1030 @type_name: Null-terminated string used as the name of the new type.
1031 @plugin: The #GTypePlugin structure to retrive the #GTypeInfo from.
1032 @flags: Bitwise combination of #GTypeFlags values.
1033 @Returns: The new type identifier.
1034 <!-- # Unused Parameters # -->
1035 @Returns: #G_TYPE_INVALID if registration failed or the new type identifier.
1038 <!-- ##### FUNCTION g_type_register_fundamental ##### -->
1040 Registers @type_id as the predefined identifier and @type_name as the
1041 name of a fundamental type. The type system uses the information
1042 contained in the #GTypeInfo structure pointed to by @info and the
1043 #GTypeFundamentalInfo structure pointed to by @finfo to manage the
1044 type and its instances. The value of @flags determines additional
1045 characteristics of the fundamental type.
1048 @type_id: A predefined #GTypeFundamentals value.
1049 @type_name: Null-terminated string used as the name of the new type.
1050 @info: The #GTypeInfo structure for this type.
1051 @finfo: The #GTypeFundamentalInfo structure for this type.
1052 @flags: Bitwise combination of #GTypeFlags values.
1053 @Returns: The predefined type identifier.
1056 <!-- ##### FUNCTION g_type_add_interface_static ##### -->
1058 Adds the static @interface_type to @instantiable_type. The information
1059 contained in the #GTypeInterfaceInfo structure pointed to by @info
1060 is used to manage the relationship.
1063 @instance_type: #GType value of an instantiable type.
1064 @interface_type: #GType value of an interface type.
1065 @info: The #GInterfaceInfo structure for this
1066 (@instance_type, @interface_type) combination.
1069 <!-- ##### FUNCTION g_type_add_interface_dynamic ##### -->
1078 <!-- ##### FUNCTION g_type_interface_add_prerequisite ##### -->
1087 <!-- ##### FUNCTION g_type_get_plugin ##### -->
1089 Returns the the #GTypePlugin structure for @type or
1090 #NULL if @type does not have a #GTypePlugin structure.
1093 @type: The #GType to retrive the plugin for.
1094 @Returns: The corresponding plugin if @type is a dynamic type,
1098 <!-- ##### FUNCTION g_type_interface_get_plugin ##### -->
1103 @implementation_type:
1107 <!-- ##### FUNCTION g_type_fundamental_next ##### -->
1109 Returns the next free fundamental type id which can be used to
1110 register a new fundamental type with g_type_register_fundamental().
1111 The returned type ID represents the highest currently registered
1112 fundamental type identifier.
1116 @Returns: The nextmost fundamental type ID to be registered,
1117 or 0 if the type system ran out of fundamental type IDs.
1120 <!-- ##### FUNCTION g_type_fundamental ##### -->
1122 Internal function, used to extract the fundamental type ID portion.
1123 use G_TYPE_FUNDAMENTAL() instead.
1126 @type_id: valid type ID
1127 @Returns: fundamental type ID
1130 <!-- ##### FUNCTION g_type_create_instance ##### -->
1132 Creates and initializes an instance of @type if @type is valid and can
1133 be instantiated. The type system only performs basic allocation and
1134 structure setups for instances, actual instance creation should happen
1135 through functions supplied by the type's fundamental type implementation.
1136 So use of g_type_create_instance() is reserved for implementators of
1137 fundamental types only. E.g. instances of the #GObject hierarchy
1138 should be created via g_object_new() and <emphasis>never</emphasis>
1139 directly through g_type_create_instance() which doesn't handle
1140 things like singleton objects or object construction.
1141 Note: Do <emphasis>not</emphasis> use this function, unless you're
1142 implementing a fundamental type. Also language bindings should <emphasis>not</emphasis>
1143 use this function but g_object_new() instead.
1146 @type: An instantiabtable type to create an instance for.
1147 @Returns: An allocated and initialized instance, subject to further
1148 treatment by the fundamental type implementation.
1151 <!-- ##### FUNCTION g_type_free_instance ##### -->
1158 <!-- ##### FUNCTION g_type_add_class_cache_func ##### -->
1167 <!-- ##### FUNCTION g_type_remove_class_cache_func ##### -->
1176 <!-- ##### FUNCTION g_type_class_unref_uncached ##### -->
1184 <!-- ##### FUNCTION g_type_value_table_peek ##### -->
1186 Returns the location of the #GTypeValueTable associated with @type.
1187 <emphasis>Note, this function should only be used from source code
1188 that implements or has internal knowledge of the implementation of
1192 @type: A #GType value.
1193 @Returns: Location of the #GTypeValueTable associated with @type or
1194 #NULL if there is no #GTypeValueTable associated with @type.