Class ZlibCompressor

Whenever the source_property is changed the target_property is updated using the same value. For instance:

  g_object_bind_property (action, "active", widget, "sensitive", 0);

Will result in the "sensitive" property of the widget #GObject instance to be updated with the same value of the "active" property of the action #GObject instance.

If flags contains %G_BINDING_BIDIRECTIONAL then the binding will be mutual: if target_property on target changes then the source_property on source will be updated as well.

The binding will automatically be removed when either the source or the target instances are finalized. To remove the binding without affecting the source and the target you can just call g_object_unref() on the returned #GBinding instance.

Removing the binding by calling g_object_unref() on it must only be done if the binding, source and target are only used from a single thread and it is clear that both source and target outlive the binding. Especially it is not safe to rely on this if the binding, source or target can be finalized from different threads. Keep another reference to the binding and use g_binding_unbind() instead to be on the safe side.

A #GObject can have multiple bindings.

This function is the language bindings friendly version of g_object_bind_property_full(), using #GClosures instead of function pointers.

Note that a single call may not consume all input (or any input at all). Also a call may produce output even if given no input, due to state stored in the converter producing output.

If any data was either produced or consumed, and then an error happens, then only the successful conversion is reported and the error is returned on the next call.

A full conversion loop involves calling this method repeatedly, each time giving it new input and space output space. When there is no more input data after the data in inbuf, the flag %G_CONVERTER_INPUT_AT_END must be set. The loop will be (unless some error happens) returning %G_CONVERTER_CONVERTED each time until all data is consumed and all output is produced, then %G_CONVERTER_FINISHED is returned instead. Note, that %G_CONVERTER_FINISHED may be returned even if %G_CONVERTER_INPUT_AT_END is not set, for instance in a decompression converter where the end of data is detectable from the data (and there might even be other data after the end of the compressed data).

When some data has successfully been converted bytes_read and is set to the number of bytes read from inbuf, and bytes_written is set to indicate how many bytes was written to outbuf. If there are more data to output or consume (i.e. unless the %G_CONVERTER_INPUT_AT_END is specified) then %G_CONVERTER_CONVERTED is returned, and if no more data is to be output then %G_CONVERTER_FINISHED is returned.

On error %G_CONVERTER_ERROR is returned and error is set accordingly. Some errors need special handling:

%G_IO_ERROR_NO_SPACE is returned if there is not enough space to write the resulting converted data, the application should call the function again with a larger outbuf to continue.

%G_IO_ERROR_PARTIAL_INPUT is returned if there is not enough input to fully determine what the conversion should produce, and the %G_CONVERTER_INPUT_AT_END flag is not set. This happens for example with an incomplete multibyte sequence when converting text, or when a regexp matches up to the end of the input (and may match further input). It may also happen when inbuf_size is zero and there is no more data to produce.

When this happens the application should read more input and then call the function again. If further input shows that there is no more data call the function again with the same data but with the %G_CONVERTER_INPUT_AT_END flag set. This may cause the conversion to finish as e.g. in the regexp match case (or, to fail again with %G_IO_ERROR_PARTIAL_INPUT in e.g. a charset conversion where the input is actually partial).

After g_converter_convert() has returned %G_CONVERTER_FINISHED the converter object is in an invalid state where its not allowed to call g_converter_convert() anymore. At this time you can only free the object or call g_converter_reset() to reset it to the initial state.

If the flag %G_CONVERTER_FLUSH is set then conversion is modified to try to write out all internal state to the output. The application has to call the function multiple times with the flag set, and when the available input has been consumed and all internal state has been produced then %G_CONVERTER_FLUSHED (or %G_CONVERTER_FINISHED if really at the end) is returned instead of %G_CONVERTER_CONVERTED. This is somewhat similar to what happens at the end of the input stream, but done in the middle of the data.

This has different meanings for different conversions. For instance in a compression converter it would mean that we flush all the compression state into output such that if you uncompress the compressed data you get back all the input data. Doing this may make the final file larger due to padding though. Another example is a regexp conversion, where if you at the end of the flushed data have a match, but there is also a potential longer match. In the non-flushed case we would ask for more input, but when flushing we treat this as the end of input and do the match.

Flushing is not always possible (like if a charset converter flushes at a partial multibyte sequence). Converters are supposed to try to produce as much output as possible and then return an error (typically %G_IO_ERROR_PARTIAL_INPUT).

This is necessary for accessors that modify multiple properties to prevent premature notification while the object is still being modified.

The value can be:

• an empty #GValue initialized by %G_VALUE_INIT, which will be automatically initialized with the expected type of the property (since GLib 2.60)
• a #GValue initialized with the expected type of the property
• a #GValue initialized with a type to which the expected type of the property can be transformed

In general, a copy is made of the property contents and the caller is responsible for freeing the memory by calling g_value_unset().

Note that g_object_get_property() is really intended for language bindings, g_object_get() is much more convenient for C programming.

When possible, eg. when signaling a property change from within the class that registered the property, you should use g_object_notify_by_pspec() instead.

Note that emission of the notify signal may be blocked with g_object_freeze_notify(). In this case, the signal emissions are queued and will be emitted (in reverse order) when g_object_thaw_notify() is called.

This function omits the property name lookup, hence it is faster than g_object_notify().

One way to avoid using g_object_notify() from within the class that registered the properties, and using g_object_notify_by_pspec() instead, is to store the GParamSpec used with g_object_class_install_property() inside a static array, e.g.:

  enum
  {
    PROP_0,
    PROP_FOO,
    PROP_LAST
  };

  static GParamSpec *properties[PROP_LAST];

  static void
  my_object_class_init (MyObjectClass *klass)
  {
    properties[PROP_FOO] = g_param_spec_int ("foo", "Foo", "The foo",
                                             0, 100,
                                             50,
                                             G_PARAM_READWRITE);
    g_object_class_install_property (gobject_class,
                                     PROP_FOO,
                                     properties[PROP_FOO]);
  }

and then notify a change on the "foo" property with:

  g_object_notify_by_pspec (self, properties[PROP_FOO]);

Since GLib 2.56, if GLIB_VERSION_MAX_ALLOWED is 2.56 or greater, the type of object will be propagated to the return type (using the GCC typeof() extension), so any casting the caller needs to do on the return type must be explicit.

In other words, if the object is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference by clearing the floating flag while leaving the reference count unchanged. If the object is not floating, then this call adds a new normal reference increasing the reference count by one.

Since GLib 2.56, the type of object will be propagated to the return type under the same conditions as for g_object_ref().

This function should only be called from object system implementations.

If the object already had an association with that name, the old association will be destroyed.

Internally, the key is converted to a #GQuark using g_quark_from_string(). This means a copy of key is kept permanently (even after object has been finalized) — so it is recommended to only use a small, bounded set of values for key in your program, to avoid the #GQuark storage growing unbounded.

void
object_add_to_user_list (GObject     *object,
                         const gchar *new_string)
{
  // the quark, naming the object data
  GQuark quark_string_list = g_quark_from_static_string ("my-string-list");
  // retrieve the old string list
  GList *list = g_object_steal_qdata (object, quark_string_list);

  // prepend new string
  list = g_list_prepend (list, g_strdup (new_string));
  // this changed 'list', so we need to set it again
  g_object_set_qdata_full (object, quark_string_list, list, free_string_list);
}
static void
free_string_list (gpointer data)
{
  GList *node, *list = data;

  for (node = list; node; node = node->next)
    g_free (node->data);
  g_list_free (list);
}

Using g_object_get_qdata() in the above example, instead of g_object_steal_qdata() would have left the destroy function set, and thus the partial string list would have been freed upon g_object_set_qdata_full().

Duplicate notifications for each property are squashed so that at most one #GObject::notify signal is emitted for each property, in the reverse order in which they have been queued.

It is an error to call this function when the freeze count is zero.

If the pointer to the #GObject may be reused in future (for example, if it is an instance variable of another object), it is recommended to clear the pointer to %NULL rather than retain a dangling pointer to a potentially invalid #GObject instance. Use g_clear_object() for this.