Properties and Atoms: GDK 3 Reference Manual

Properties and Atoms

Properties and Atoms — Functions to manipulate properties on windows

Functions

#define	GDK_ATOM_TO_POINTER()
#define	GDK_POINTER_TO_ATOM()
gint	gdk_text_property_to_utf8_list_for_display ()
gchar *	gdk_utf8_to_string_target ()
GdkAtom	gdk_atom_intern ()
GdkAtom	gdk_atom_intern_static_string ()
gchar *	gdk_atom_name ()
gboolean	gdk_property_get ()
void	gdk_property_change ()
void	gdk_property_delete ()

Types and Values

	GdkAtom
#define	GDK_NONE
enum	GdkPropMode

Includes

#include <gdk/gdk.h>

Description

Each window under X can have any number of associated “properties” attached to it. Properties are arbitrary chunks of data identified by “atom”s. (An “atom” is a numeric index into a string table on the X server. They are used to transfer strings efficiently between clients without having to transfer the entire string.) A property has an associated type, which is also identified using an atom.

A property has an associated “format”, an integer describing how many bits are in each unit of data inside the property. It must be 8, 16, or 32. When data is transferred between the server and client, if they are of different endianesses it will be byteswapped as necessary according to the format of the property. Note that on the client side, properties of format 32 will be stored with one unit per long, even if a long integer has more than 32 bits on the platform. (This decision was apparently made for Xlib to maintain compatibility with programs that assumed longs were 32 bits, at the expense of programs that knew better.)

The functions in this section are used to add, remove and change properties on windows, to convert atoms to and from strings and to manipulate some types of data commonly stored in X window properties.

Functions

GDK_ATOM_TO_POINTER()

#define GDK_ATOM_TO_POINTER(atom) (atom)

Converts a GdkAtom into a pointer type.

Parameters

atom

a GdkAtom.

GDK_POINTER_TO_ATOM()

#define GDK_POINTER_TO_ATOM(ptr)  ((GdkAtom)(ptr))

Extracts a GdkAtom from a pointer. The GdkAtom must have been stored in the pointer with GDK_ATOM_TO_POINTER().

Parameters

ptr

a pointer containing a GdkAtom.

gdk_text_property_to_utf8_list_for_display ()

gint
gdk_text_property_to_utf8_list_for_display
                               (GdkDisplay *display,
                                GdkAtom encoding,
                                gint format,
                                const guchar *text,
                                gint length,
                                gchar ***list);

Converts a text property in the given encoding to a list of UTF-8 strings.

Parameters

display	a GdkDisplay
encoding	an atom representing the encoding of the text
format	the format of the property
text	the text to convert.	[array length=length]
length	the length of `text` , in bytes
list	location to store the list of strings or `NULL`. The list should be freed with `g_strfreev()`.	[out][array zero-terminated=1]

Returns

the number of strings in the resulting list

Since: 2.2

gdk_utf8_to_string_target ()

gchar *
gdk_utf8_to_string_target (const gchar *str);

Converts an UTF-8 string into the best possible representation as a STRING. The representation of characters not in STRING is not specified; it may be as pseudo-escape sequences \x{ABCD}, or it may be in some other form of approximation.

Parameters

str

a UTF-8 string

Returns

the newly-allocated string, or NULL if the conversion failed. (It should not fail for any properly formed UTF-8 string unless system limits like memory or file descriptors are exceeded.).

[nullable]

gdk_atom_intern ()

GdkAtom
gdk_atom_intern (const gchar *atom_name,
                 gboolean only_if_exists);

Finds or creates an atom corresponding to a given string.

Parameters

atom_name	a string.
only_if_exists	if `TRUE`, GDK is allowed to not create a new atom, but just return `GDK_NONE` if the requested atom doesn’t already exists. Currently, the flag is ignored, since checking the existance of an atom is as expensive as creating it.

Returns

the atom corresponding to atom_name .

[transfer none]

gdk_atom_intern_static_string ()

GdkAtom
gdk_atom_intern_static_string (const gchar *atom_name);

Finds or creates an atom corresponding to a given string.

Note that this function is identical to gdk_atom_intern() except that if a new GdkAtom is created the string itself is used rather than a copy. This saves memory, but can only be used if the string will always exist. It can be used with statically allocated strings in the main program, but not with statically allocated memory in dynamically loaded modules, if you expect to ever unload the module again (e.g. do not use this function in GTK+ theme engines).

Parameters

atom_name

a static string

Returns

the atom corresponding to atom_name .

[transfer none]

Since: 2.10

gdk_atom_name ()

gchar *
gdk_atom_name (GdkAtom atom);

Determines the string corresponding to an atom.

Parameters

atom

a GdkAtom.

Returns

a newly-allocated string containing the string corresponding to atom . When you are done with the return value, you should free it using g_free().

gdk_property_get ()

gboolean
gdk_property_get (GdkWindow *window,
                  GdkAtom property,
                  GdkAtom type,
                  gulong offset,
                  gulong length,
                  gint pdelete,
                  GdkAtom *actual_property_type,
                  gint *actual_format,
                  gint *actual_length,
                  guchar **data);

Retrieves a portion of the contents of a property. If the property does not exist, then the function returns FALSE, and GDK_NONE will be stored in actual_property_type .

The XGetWindowProperty() function that gdk_property_get() uses has a very confusing and complicated set of semantics. Unfortunately, gdk_property_get() makes the situation worse instead of better (the semantics should be considered undefined), and also prints warnings to stderr in cases where it should return a useful error to the program. You are advised to use XGetWindowProperty() directly until a replacement function for gdk_property_get() is provided.

Parameters

window	a GdkWindow
property	the property to retrieve
type	the desired property type, or `GDK_NONE`, if any type of data is acceptable. If this does not match the actual type, then `actual_format` and `actual_length` will be filled in, a warning will be printed to stderr and no data will be returned.
offset	the offset into the property at which to begin retrieving data, in 4 byte units.
length	the length of the data to retrieve in bytes. Data is considered to be retrieved in 4 byte chunks, so `length` will be rounded up to the next highest 4 byte boundary (so be careful not to pass a value that might overflow when rounded up).
pdelete	if `TRUE`, delete the property after retrieving the data.
actual_property_type	location to store the actual type of the property.	[out][transfer none]
actual_format	location to store the actual return format of the data; either 8, 16 or 32 bits.	[out]
actual_length	location to store the length of the retrieved data, in bytes. Data returned in the 32 bit format is stored in a long variable, so the actual number of 32 bit elements should be be calculated via `actual_length` / sizeof(glong) to ensure portability to 64 bit systems.
data	location to store a pointer to the data. The retrieved data should be freed with `g_free()` when you are finished using it.	[out][array length=actual_length][transfer full]

Returns

TRUE if data was successfully received and stored in data , otherwise FALSE.

gdk_property_change ()

void
gdk_property_change (GdkWindow *window,
                     GdkAtom property,
                     GdkAtom type,
                     gint format,
                     GdkPropMode mode,
                     const guchar *data,
                     gint nelements);

Changes the contents of a property on a window.

[skip]

Parameters

window	a GdkWindow
property	the property to change
type	the new type for the property. If `mode` is `GDK_PROP_MODE_PREPEND` or `GDK_PROP_MODE_APPEND`, then this must match the existing type or an error will occur.
format	the new format for the property. If `mode` is `GDK_PROP_MODE_PREPEND` or `GDK_PROP_MODE_APPEND`, then this must match the existing format or an error will occur.
mode	a value describing how the new data is to be combined with the current data.
data	the data (a `guchar ` `gushort `, or `gulong `, depending on `format`* ), cast to a `guchar *`.
nelements	the number of elements of size determined by the format, contained in `data` .

gdk_property_delete ()

void
gdk_property_delete (GdkWindow *window,
                     GdkAtom property);

Deletes a property from a window.

Parameters

window	a GdkWindow
property	the property to delete

Types and Values

GdkAtom

typedef struct _GdkAtom GdkAtom;

An opaque type representing a string as an index into a table of strings on the X server.

GDK_NONE

#define GDK_NONE            _GDK_MAKE_ATOM (0)

A null value for GdkAtom, used in a similar way as None in the Xlib API.

enum GdkPropMode

Describes how existing data is combined with new data when using gdk_property_change().

Members

GDK_PROP_MODE_REPLACE	the new data replaces the existing data.
GDK_PROP_MODE_PREPEND	the new data is prepended to the existing data.
GDK_PROP_MODE_APPEND	the new data is appended to the existing data.