glib/docs/reference/gobject/tmpl/generic_values.sgml

<!-- ##### SECTION Title ##### -->
Generic Values

<!-- ##### SECTION Short_Description ##### -->
A polymorphic type that can hold values of any other type.

<!-- ##### SECTION Long_Description ##### -->
<para>
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.
</para>

<!-- ##### SECTION See_Also ##### -->
<para>
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.
</para>

<!-- ##### MACRO G_VALUE_HOLDS ##### -->
<para>
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.
</para>

@value: 
@type: 


<!-- ##### MACRO G_VALUE_TYPE ##### -->
<para>
Returns the type identifier of @value.
</para>

@value: A #GValue structure.


<!-- ##### MACRO G_VALUE_TYPE_NAME ##### -->
<para>
Returns the type name of @value.
</para>

@value: A #GValue structure.


<!-- ##### MACRO G_TYPE_IS_VALUE ##### -->
<para>
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.
</para>

@type: 	  A #GType value.
@Returns: Whether @type is suitable as a #GValue type.


<!-- ##### MACRO G_TYPE_IS_VALUE_ABSTRACT ##### -->
<para>

</para>

@type: 


<!-- ##### MACRO G_IS_VALUE ##### -->
<para>
Returns #TRUE if @value is a valid and initialized #GValue structure.
</para>

@value: A #GValue structure.


<!-- ##### USER_FUNCTION GValueExchange ##### -->
<para>

</para>

@value1: 
@value2: 


<!-- ##### STRUCT GValue ##### -->
<para>
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.
</para>


<!-- ##### MACRO G_TYPE_VALUE ##### -->
<para>

</para>



<!-- ##### MACRO G_TYPE_VALUE_ARRAY ##### -->
<para>

</para>



<!-- ##### FUNCTION g_value_init ##### -->
<para>
Initializes @value with the default value of @type.
</para>

@value: 		A zero-filled (uninitialized) #GValue structure.
@g_type: 	Type the #GValue should hold values of.
@Returns: 


<!-- ##### FUNCTION g_value_copy ##### -->
<para>
Copies the value of @src_value into @dest_value.
</para>

@src_value: 	An initialized #GValue structure.
@dest_value: 	An initialized #GValue structure of the same type as @src_value.


<!-- ##### FUNCTION g_value_reset ##### -->
<para>
Clears the current value in @value and resets it to the default value
(as if the value had just been initialized).
</para>

@value: 	An initialized #GValue structure.
@Returns: 


<!-- ##### FUNCTION g_value_unset ##### -->
<para>
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.
</para>

@value: 	An initialized #GValue structure.


<!-- ##### FUNCTION g_value_fits_pointer ##### -->
<para>
Determines if @value will fit inside the size of a pointer value.
This is an internal function introduced mainly for C marshallers.
</para>

@value: 		An initialized #GValue structure.
@Returns: 	#TRUE if @value will fit inside a pointer value.


<!-- ##### FUNCTION g_value_peek_pointer ##### -->
<para>
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.
</para>

@value: 		An initialized #GValue structure.
@Returns: 	#TRUE if @value will fit inside a pointer value.


<!-- ##### FUNCTION g_value_type_compatible ##### -->
<para>

</para>

@src_type: 
@dest_type: 
@Returns: 


<!-- ##### FUNCTION g_value_type_transformable ##### -->
<para>
Check whether g_value_transform() is able to transform values
of type @src_type into values of type @dest_type.
</para>

@src_type:  Source type.
@dest_type: Target type.
@Returns:   %TRUE if the transformation is possible, %FALSE otherwise.


<!-- ##### FUNCTION g_value_transform ##### -->
<para>
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).
</para>

@src_value:  Source value.
@dest_value: Target value.
@Returns:    Whether a transformation rule was found and could be applied.
             Upon failing transformations, @dest_value is left untouched.


<!-- ##### USER_FUNCTION GValueTransform ##### -->
<para>

</para>

@src_value: 
@dest_value: 


<!-- ##### FUNCTION g_value_register_transform_func ##### -->
<para>

</para>

@src_type: 
@dest_type: 
@transform_func: 


<!-- ##### FUNCTION g_strdup_value_contents ##### -->
<para>

</para>

@value: 
@Returns: