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3a216c72e2
It’s not particularly clear why both these exist and why you need to use both of them when creating a `GValue` — but you do. Try and clarify things in the documentation. In particular, replace use of the term ‘uninitialised’ (referring to a `GValue` which has been set to `G_VALUE_INIT` but not yet had `g_value_init()` called on it) with ‘zero-filled (cleared)’ instead. ‘uninitialised’ doesn’t make sense to describe a variable which, in C terms, has just been initialised by assigning `G_VALUE_INIT` to it. ‘cleared’ is a bit less overloaded as a term. Add some code examples to hopefully make things clearer too. Signed-off-by: Philip Withnall <pwithnall@gnome.org>
256 lines
7.5 KiB
C
256 lines
7.5 KiB
C
/* GObject - GLib Type, Object, Parameter and Signal Library
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* Copyright (C) 1997-1999, 2000-2001 Tim Janik and Red Hat, Inc.
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*
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* SPDX-License-Identifier: LGPL-2.1-or-later
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General
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* Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*
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* gvalue.h: generic GValue functions
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*/
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#ifndef __G_VALUE_H__
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#define __G_VALUE_H__
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#if !defined (__GLIB_GOBJECT_H_INSIDE__) && !defined (GOBJECT_COMPILATION)
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#error "Only <glib-object.h> can be included directly."
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#endif
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#include <gobject/gtype.h>
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G_BEGIN_DECLS
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/* --- type macros --- */
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/**
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* G_TYPE_IS_VALUE:
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* @type: a type
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*
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* Checks whether the passed in type ID can be used for
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* [method@GObject.Value.init].
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*
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* That is, this macro checks whether this type provides an implementation
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* of the [struct@GObject.TypeValueTable] functions required to be able to
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* create a [struct@GObject.Value] instance.
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*
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* Returns: Whether @type is suitable as a [struct@GObject.Value] type.
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*/
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#define G_TYPE_IS_VALUE(type) (g_type_check_is_value_type (type))
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/**
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* G_IS_VALUE:
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* @value: a [struct@GObject.Value] structure
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*
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* Checks if @value is a valid and initialized [struct@GObject.Value] structure.
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*
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* Returns: true on success; false otherwise
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*/
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#define G_IS_VALUE(value) (G_TYPE_CHECK_VALUE (value))
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/**
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* G_VALUE_TYPE:
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* @value: a [struct@GObject.Value] structure
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*
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* Get the type identifier of @value.
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*
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* Returns: the type ID
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*/
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#define G_VALUE_TYPE(value) (((GValue*) (value))->g_type)
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/**
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* G_VALUE_TYPE_NAME:
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* @value: a [struct@GObject.Value] structure
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*
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* Gets the name of the type of @value.
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*
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* Returns: the type name
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*/
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#define G_VALUE_TYPE_NAME(value) (g_type_name (G_VALUE_TYPE (value)))
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/**
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* G_VALUE_HOLDS:
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* @value: (not nullable): a [struct@GObject.Value] structure
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* @type: a [type@GObject.Type]
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*
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* Checks if @value holds a value of @type.
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*
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* This macro will also check for `value != NULL` and issue a
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* warning if the check fails.
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*
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* Returns: true if @value is non-`NULL` and holds a value of the given @type;
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* false otherwise
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*/
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#define G_VALUE_HOLDS(value,type) (G_TYPE_CHECK_VALUE_TYPE ((value), (type)))
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/* --- typedefs & structures --- */
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/**
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* GValueTransform:
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* @src_value: source value
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* @dest_value: target value
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*
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* The type of value transformation functions which can be registered with
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* [func@GObject.Value.register_transform_func].
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*
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* @dest_value will be initialized to the correct destination type.
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*/
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typedef void (*GValueTransform) (const GValue *src_value,
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GValue *dest_value);
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/**
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* GValue:
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*
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* An opaque structure used to hold different types of values.
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*
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* Before it can be used, a `GValue` has to be initialized to a specific type by
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* calling [method@GObject.Value.init] on it.
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*
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* Many types which are stored within a `GValue` need to allocate data on the
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* heap, so [method@GObject.Value.unset] must always be called on a `GValue` to
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* free any such data once you’re finished with the `GValue`, even if the
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* `GValue` itself is stored on the stack.
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*
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* The data within the structure has protected scope: it is accessible only
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* to functions within a [struct@GObject.TypeValueTable] structure, or
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* implementations of the `g_value_*()` API. That is, code which implements new
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* fundamental types.
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*
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* `GValue` users cannot make any assumptions about how data is stored
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* within the 2 element @data union, and the @g_type member should
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* only be accessed through the [func@GObject.VALUE_TYPE] macro and related
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* macros.
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*/
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struct _GValue
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{
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/*< private >*/
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GType g_type;
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/* public for GTypeValueTable methods */
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union {
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gint v_int;
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guint v_uint;
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glong v_long;
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gulong v_ulong;
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gint64 v_int64;
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guint64 v_uint64;
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gfloat v_float;
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gdouble v_double;
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gpointer v_pointer;
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} data[2];
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};
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/* --- prototypes --- */
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GOBJECT_AVAILABLE_IN_ALL
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GValue* g_value_init (GValue *value,
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GType g_type);
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GOBJECT_AVAILABLE_IN_ALL
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void g_value_copy (const GValue *src_value,
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GValue *dest_value);
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GOBJECT_AVAILABLE_IN_ALL
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GValue* g_value_reset (GValue *value);
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GOBJECT_AVAILABLE_IN_ALL
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void g_value_unset (GValue *value);
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GOBJECT_AVAILABLE_IN_ALL
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void g_value_set_instance (GValue *value,
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gpointer instance);
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GOBJECT_AVAILABLE_IN_2_42
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void g_value_init_from_instance (GValue *value,
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gpointer instance);
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/* --- private --- */
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GOBJECT_AVAILABLE_IN_ALL
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gboolean g_value_fits_pointer (const GValue *value);
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GOBJECT_AVAILABLE_IN_ALL
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gpointer g_value_peek_pointer (const GValue *value);
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/* --- implementation details --- */
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GOBJECT_AVAILABLE_IN_ALL
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gboolean g_value_type_compatible (GType src_type,
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GType dest_type);
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GOBJECT_AVAILABLE_IN_ALL
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gboolean g_value_type_transformable (GType src_type,
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GType dest_type);
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GOBJECT_AVAILABLE_IN_ALL
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gboolean g_value_transform (const GValue *src_value,
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GValue *dest_value);
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GOBJECT_AVAILABLE_IN_ALL
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void g_value_register_transform_func (GType src_type,
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GType dest_type,
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GValueTransform transform_func);
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/**
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* G_VALUE_NOCOPY_CONTENTS:
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*
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* Flag to indicate that allocated data in a [struct@GObject.Value] shouldn’t be
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* copied.
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*
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* If passed to [func@GObject.VALUE_COLLECT], allocated data won’t be copied
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* but used verbatim. This does not affect ref-counted types like objects.
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*
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* This does not affect usage of [method@GObject.Value.copy]: the data will
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* be copied if it is not ref-counted.
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*
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* This flag should be checked by implementations of
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* [callback@GObject.TypeValueFreeFunc], [callback@GObject.TypeValueCollectFunc]
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* and [callback@GObject.TypeValueLCopyFunc].
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*/
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#define G_VALUE_NOCOPY_CONTENTS (1 << 27)
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/**
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* G_VALUE_INTERNED_STRING:
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*
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* Flag to indicate that a string in a [struct@GObject.Value] is canonical and
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* will exist for the duration of the process.
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*
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* See [method@GObject.Value.set_interned_string].
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*
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* This flag should be checked by implementations of
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* [callback@GObject.TypeValueFreeFunc], [callback@GObject.TypeValueCollectFunc]
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* and [callback@GObject.TypeValueLCopyFunc].
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*
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* Since: 2.66
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*/
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#define G_VALUE_INTERNED_STRING (1 << 28) GOBJECT_AVAILABLE_MACRO_IN_2_66
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/**
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* G_VALUE_INIT:
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*
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* Clears a [struct@GObject.Value] to zero at declaration time.
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*
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* A [struct@GObject.Value] must be cleared and then initialized before it can
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* be used. This macro can be assigned to a variable instead of an explicit
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* `{ 0 }` when declaring it, but it cannot be assigned to a variable after
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* declaration time.
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*
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* After the [struct@GObject.Value] is cleared, it must be initialized by
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* calling [method@GObject.Value.init] on it before any other methods can be
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* called on it.
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*
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* ```c
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* GValue value = G_VALUE_INIT;
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*
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* g_value_init (&value, SOME_G_TYPE);
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* …
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* g_value_unset (&value);
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* ```
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*
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* Since: 2.30
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*/
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#define G_VALUE_INIT { 0, { { 0 } } }
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G_END_DECLS
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#endif /* __G_VALUE_H__ */
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