Properties and Atoms

Properties and Atoms — Functions to manipulate properties on windows

Synopsis

#include <gdk/gdk.h>

                    GdkAtom;
#define             GDK_ATOM_TO_POINTER                 (atom)
#define             GDK_POINTER_TO_ATOM                 (ptr)
#define             GDK_NONE
gint                gdk_text_property_to_text_list      (GdkAtom encoding,
                                                         gint format,
                                                         const guchar *text,
                                                         gint length,
                                                         gchar ***list);
gint                gdk_text_property_to_text_list_for_display
                                                        (GdkDisplay *display,
                                                         GdkAtom encoding,
                                                         gint format,
                                                         const guchar *text,
                                                         gint length,
                                                         gchar ***list);
void                gdk_free_text_list                  (gchar **list);
gint                gdk_text_property_to_utf8_list      (GdkAtom encoding,
                                                         gint format,
                                                         const guchar *text,
                                                         gint length,
                                                         gchar ***list);
gint                gdk_text_property_to_utf8_list_for_display
                                                        (GdkDisplay *display,
                                                         GdkAtom encoding,
                                                         gint format,
                                                         const guchar *text,
                                                         gint length,
                                                         gchar ***list);
gint                gdk_string_to_compound_text         (const gchar *str,
                                                         GdkAtom *encoding,
                                                         gint *format,
                                                         guchar **ctext,
                                                         gint *length);
gint                gdk_string_to_compound_text_for_display
                                                        (GdkDisplay *display,
                                                         const gchar *str,
                                                         GdkAtom *encoding,
                                                         gint *format,
                                                         guchar **ctext,
                                                         gint *length);
void                gdk_free_compound_text              (guchar *ctext);
gchar *             gdk_utf8_to_string_target           (const gchar *str);
gboolean            gdk_utf8_to_compound_text           (const gchar *str,
                                                         GdkAtom *encoding,
                                                         gint *format,
                                                         guchar **ctext,
                                                         gint *length);
gboolean            gdk_utf8_to_compound_text_for_display
                                                        (GdkDisplay *display,
                                                         const gchar *str,
                                                         GdkAtom *encoding,
                                                         gint *format,
                                                         guchar **ctext,
                                                         gint *length);
GdkAtom             gdk_atom_intern                     (const gchar *atom_name,
                                                         gboolean only_if_exists);
GdkAtom             gdk_atom_intern_static_string       (const gchar *atom_name);
gchar*              gdk_atom_name                       (GdkAtom atom);
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);
void                gdk_property_change                 (GdkWindow *window,
                                                         GdkAtom property,
                                                         GdkAtom type,
                                                         gint format,
                                                         GdkPropMode mode,
                                                         const guchar *data,
                                                         gint nelements);
enum                GdkPropMode;
void                gdk_property_delete                 (GdkWindow *window,
                                                         GdkAtom property);

Description

Each window under X can have any number of associated properties attached to it. Properties are arbitrary chunks of data identified by atoms. (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.

Details

GdkAtom

typedef struct _GdkAtom GdkAtom;

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

GDK_ATOM_TO_POINTER()

#define GDK_ATOM_TO_POINTER(atom) (atom)

Converts a GdkAtom into a pointer type.

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().

ptr :

 a pointer containing a GdkAtom.

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.

gdk_text_property_to_text_list ()

gint                gdk_text_property_to_text_list      (GdkAtom encoding,
                                                         gint format,
                                                         const guchar *text,
                                                         gint length,
                                                         gchar ***list);

Converts a text string from the encoding as it is stored in a property into an array of strings in the encoding of the current local. (The elements of the array represent the nul-separated elements of the original text string.)

encoding :

 an atom representing the encoding. The most common values for this are STRING, or COMPOUND_TEXT. This is value used as the type for the property.

format :

 the format of the property.

text :

 the text data.

length :

 the length of the property, in items.

list :

 location to store a terminated array of strings in the encoding of the current locale. This array should be freed using gdk_free_text_list().

Returns :

 the number of strings stored in list, or 0, if the conversion failed.

gdk_text_property_to_text_list_for_display ()

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

Convert a text string from the encoding as it is stored in a property into an array of strings in the encoding of the current locale. (The elements of the array represent the nul-separated elements of the original text string.)

display :

 The GdkDisplay where the encoding is defined.

encoding :

 an atom representing the encoding. The most common values for this are STRING, or COMPOUND_TEXT. This is value used as the type for the property.

format :

 the format of the property.

text :

 The text data.

length :

 The number of items to transform.

list :

 location to store a terminated array of strings in the encoding of the current locale. This array should be freed using gdk_free_text_list().

Returns :

 the number of strings stored in list, or 0, if the conversion failed.

Since 2.2

gdk_free_text_list ()

void                gdk_free_text_list                  (gchar **list);

Frees the array of strings created by gdk_text_property_to_text_list().

list :

 the value stored in the list parameter by a call to gdk_text_property_to_text_list().

gdk_text_property_to_utf8_list ()

gint                gdk_text_property_to_utf8_list      (GdkAtom encoding,
                                                         gint format,
                                                         const guchar *text,
                                                         gint length,
                                                         gchar ***list);

Convert a text property in the giving encoding to a list of UTF-8 strings.

encoding :

 an atom representing the encoding of the text

format :

 the format of the property

text :

 the text to convert

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().

Returns :

 the number of strings in the resulting list.

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.

display :

 a GdkDisplay

encoding :

 an atom representing the encoding of the text

format :

 the format of the property

text :

 the text to convert

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().

Returns :

 the number of strings in the resulting list.

Since 2.2

gdk_string_to_compound_text ()

gint                gdk_string_to_compound_text         (const gchar *str,
                                                         GdkAtom *encoding,
                                                         gint *format,
                                                         guchar **ctext,
                                                         gint *length);

Converts a string from the encoding of the current locale into a form suitable for storing in a window property.

str :

 a nul-terminated string.

encoding :

 location to store the encoding atom (to be used as the type for the property).

format :

 location to store the format for the property.

ctext :

 location to store newly allocated data for the property.

length :

 location to store the length of ctext in items.

Returns :

 0 upon sucess, non-zero upon failure.

gdk_string_to_compound_text_for_display ()

gint                gdk_string_to_compound_text_for_display
                                                        (GdkDisplay *display,
                                                         const gchar *str,
                                                         GdkAtom *encoding,
                                                         gint *format,
                                                         guchar **ctext,
                                                         gint *length);

Convert a string from the encoding of the current locale into a form suitable for storing in a window property.

display :

 the GdkDisplay where the encoding is defined.

str :

 a nul-terminated string.

encoding :

 location to store the encoding atom (to be used as the type for the property).

format :

 location to store the format of the property

ctext :

 location to store newly allocated data for the property.

length :

 the length of text, in bytes

Returns :

 0 upon success, non-zero upon failure.

Since 2.2

gdk_free_compound_text ()

void                gdk_free_compound_text              (guchar *ctext);

Frees the data returned from gdk_string_to_compound_text().

ctext :

 The pointer stored in ctext from a call to gdk_string_to_compound_text().

gdk_utf8_to_string_target ()

gchar *             gdk_utf8_to_string_target           (const gchar *str);

Convert 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.

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.)

gdk_utf8_to_compound_text ()

gboolean            gdk_utf8_to_compound_text           (const gchar *str,
                                                         GdkAtom *encoding,
                                                         gint *format,
                                                         guchar **ctext,
                                                         gint *length);

Convert from UTF-8 to compound text.

str :

 a UTF-8 string

encoding :

 location to store resulting encoding

format :

 location to store format of the result

ctext :

 location to store the data of the result

length :

 location to store the length of the data stored in ctext

Returns :

 TRUE if the conversion succeeded, otherwise false.

gdk_utf8_to_compound_text_for_display ()

gboolean            gdk_utf8_to_compound_text_for_display
                                                        (GdkDisplay *display,
                                                         const gchar *str,
                                                         GdkAtom *encoding,
                                                         gint *format,
                                                         guchar **ctext,
                                                         gint *length);

Converts from UTF-8 to compound text.

display :

 a GdkDisplay

str :

 a UTF-8 string

encoding :

 location to store resulting encoding

format :

 location to store format of the result

ctext :

 location to store the data of the result

length :

 location to store the length of the data stored in ctext

Returns :

 TRUE if the conversion succeeded, otherwise FALSE.

Since 2.2

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.

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.

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).

atom_name :

 a static string

Returns :

 the atom corresponding to atom_name

Since 2.10

gdk_atom_name ()

gchar*              gdk_atom_name                       (GdkAtom atom);

Determines the string corresponding to an atom.

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.

Note

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.

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.

actual_format :

 location to store the actual return format of the data; either 8, 16 or 32 bits.

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.

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.

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.

enum GdkPropMode

typedef enum
{
  GDK_PROP_MODE_REPLACE,
  GDK_PROP_MODE_PREPEND,
  GDK_PROP_MODE_APPEND
} GdkPropMode;

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

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.

gdk_property_delete ()

void                gdk_property_delete                 (GdkWindow *window,
                                                         GdkAtom property);

Deletes a property from a window.

window :

 a GdkWindow.

property :

 the property to delete.
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